REVIEW FOR TEST 1, CHAPTERS 2-4
Review Questions - You should review all questions at the end of each
chapter. However, particular attention should be payed to the follow-
ing ones.
A good way to study using this sheet is to read the question from the
book and try to answer it. Then check your answer with that below.
Questions covered in this review:
Ch 2 -- 2, 3, 4, 5, 6
Ch 3 -- 1, 2, 3, 5, 7, 8, 9, 10, 11, 12, 13
Ch 4 -- 1, 2, 3, 4, 5, 6, 11, 14
Chapter 2
2. A scalar has a numerical value and physical units only. Think of
"scalar" in terms of a scale, for example, a temperature scale. A
vector, however, has both magnitude (how "large" it is) and direction.
Scalars: volume, area, time, length, speed, energy, work, power
Vectors: displacement, velocity, acceleration, force
3. Speed is the rate at which distance is being covered and is just
a positive number with units of distance/time. Velocity is speed
plus direction. Speed is the magnitude of the velocity (with no re-
ference to direction).
speed: 55 mi/h velocity: 55 mi/h to the NW
4. Since velocity includes both speed and direction, a change of either
one constitutes an acceleration. That is, an object moving in a
curved path at constant speed is accelerating because its direction
of motion is changing, hence its velocity is changing also. For this
case acceleration is not the rate of change of speed but the rate of
change of the direction of motion.
5. As explained for question 4, an object can be changing its direction
of motion, keeping its speed steady, and be accelerating. An example
of this we covered in class is circular motion. An object moving in
a circle at constant speed experiences an acceleration directed to-
ward the center of the circle, called the centripetal acceleration
6. The acceleration of a freely falling body (a body moving solely under
the influence of gravity) is always the acceleration of gravity. It
does not matter if the object is initially moving upwards, downwards,
or sideways. (Note that "falling" has a different meaning in physics
than in everyday language. A ball thrown upward is falling as far as
physicists are concerned because it is moving only under the influ-
ence of gravity.) At sea level the acceleration of a freely-falling
body is 9.8 m/s/s toward the center of the earth, whether the body is,
at the moment, ascending or descending. The acceleration of an object
thrown upward is still 9.8 m/s/s downwards at its highest point,
despite its coming to an instantaneous stop at that point. At the top
of its motion it changes direction, and a change in direction is an
acceleration.
Chapter 3
1. An object must have zero acceleration to maintain a constant velo-
city. By Newton's second law this means the net force acting on
the object must be zero. It does NOT mean that no forces can be
acting on the object. The net force can still be zero if the forces
acting on it cancel out.
2. The net force acting on the object must also be constant for the
acceleration to be constant, because, from Newton's second law
(F = ma, or, a = F/m), if "F" changes, "a" must change also. Now,
if several forces are acting on a body, they can change and still
keep the acceleration constant so long as the NET force, the sum of
all these forces, remains constant.
3. Since the gun (through the medium of compressed gases caused by the
exploding charge in the cartridge) exerts a force on the bullet, the
bullet MUST exert an equal and opposite force (again by means of the
gases) on the gun. However, Newton's second law states a = F/m,
which says the acceleration is less the greater the mass. The acce-
leration of the bullet is very large because its mass is small, but
the acceleration of the gun is much less due to its greater mass.
5. Maximum force = 40 lb + 30 lb = 70 lb. In this case the forces are
acting in the same direction.
Minimum force = 40 lb - 30 lb = 10 lb. In this case the forces are
acting in opposite directions.
7. Mass is the amount of matter an object has, that is, the number of
protons + neutrons + electrons expressed in an appropriate unit such
as the kilogram. Mass is also the measure of inertia: The more
mass an object has the harder it is to change its state of motion.
Weight is the force of gravity on an object. Amazingly enough (when
you think about it) the force of gravity is proportional to the iner-
tial mass through the relationship W = mg.
8. The equation of the lever states that for rotational equilibrium to
hold, the input force times its distance from the fulcrum (the input
torque) must equal the output force times its distance from the ful-
crum (the output torque). That is, in the figure
F1 F2
| |
| |
|<-- L1 --><------ L2 ------>|
V____________________________V
^
fulcrum
F1 x L1 = F2 x L2, where one of the forces can be considered the
input force and the other the output force. Say F2 is the input
force (for example, the force applied to a crowbar, etc.). You
can reduce this force if you can lengthen L2, since it's the torque,
the product of F2 times L2, that is responsible for rotating the
lever about the fulcrum by working against F1 times L1, the output
torque. (See 9 and 10 below for a discussion of equilibrium).
9. There are two types of equilibrium; translational and rotational.
A body that is not accelerating is said to be in translational equi-
librium. (Note that the body may be moving, just not accelerating.)
Hence a body in translational equilibrium must have zero net force
acting on it. This does not mean no forces are acting on it, just
that any forces acting on it must cancel. The building you are in
is (in the absence of earthquake or nuclear attack) in translational
equilbrium. Its weight is supported by the force exerted by the
ground on its foundation. These two forces cancel out.
10. Translational equilibrium: occurs when a body has no acceleration.
Rotational equilibrium: occurs when a body is either not rotating
at all or is rotating at a constant rate.
Condition for translational equilibrium: net force acting on a body
must be zero.
Condition for rotational equilibrium: net torque acting on a body
must be zero.
11. The weight of the object would be reduced by a factor of about 1/6,
since the gravity of the moon at its surface is six times weaker than
the gravity of the earth at its surface. The mass, being the amount
of matter present, is the same in both places.
12. Since the direction of motion of the object is changing, we have
seen from the previous chapter that its velocity is changing,
which means, in turn, that it has an acceleration. This accelera-
tion is directed toward the center of the motion (the center of the
circle it is traveling in) and is called the centripetal acceleration
By Newton's second law we know there must be a net force causing
this acceleration, the centripetal force. In the case of a ball on
a string moving in a circle, this force is the tension on the string
pulling on the ball. In the case of a satellite in a circular orbit
about the earth, this force is the force of gravity acting on the
satellite (its weight). The centripetal force. like the centripetal
acceleration, must always point toward the center of the motion.
13. The tension of the string acting on the ball causes the ball to move
in a circle. This tension is the centripetal force. When the string
is released, the tension goes to zero and there is no longer any force
to cause the ball to move in a circle. Hence the ball just continues
to move in whatever direction it was going when you released the
string (although gravity acts to turn it down toward the earth).
This follows from Newton's first law of motion.
Chapter 4
1. The work performed by a force acting on an object equals that force
times the distance the object travels. The performance of work on
an object changes the energy of that object. Work is positive if
the force is in the same direction as the motion. Work is negative
if the force is directed opposite to the motion. Work is zero if
the force is perpendicular to the motion. Work is also zero if a
force is applied to an object that remains stationary. Work has the
units of joules (newton-meters) in SI and pound-feet in British.
Power can be defined in a couple of similar ways. It has the units
in SI of joules per second (watts) and in British of horsepower.
- It is the rate at which work is done.
- It is the rate of expenditure of energy.
Energy is a property of matter imparted by doing work. There are
three forms we talked about in this chapter.
- kinetic energy (KE) = the energy of motion
- potential energy (PE) = the energy of position due to the action
of a conservative force (gravity, in our case)
- heat energy = the energy of the random motion of atoms or molecules
- kinetic energy plus potential energy is called mechanical energy
2. A force acting on an object that remains stationary does no work.
A force acting on an object in a direction that is perpendicular to
the motion of the object does no work.
3. In the broad sense conservation of energy means that energy can be
changed from one form to another but not created or destroyed.
In the case of mechanical energy, mechanical energy (kinetic plus
potential) is conserved for an object if only conservative forces
are performing work on the object. (The only conservative force we
cover in this chapter is gravity.) When this is true the mechanical
energy of the object remains the same (PE + KE = constant).
4. In this case mechanical energy is not conserved, because PE remains
the same (cart on level ground), but the KE gets smaller. The non-
conservative force acting in this case is friction. The KE that is
lost is converted into heat energy.
5. Conservation of energy says energy cannot be created out of nothing.
So, no, a machine cannot create energy. A machine can only convert
one form of energy into another. However...(#6)
6. Machines can produce an output force different than the input force.
This is the mechanism of the lever. The lever equation is F1 x L1 =
F2 x L2 for a lever in rotational equilibrium. Let F1 be the input
force, F2 the output force, L1 the distance from F1 to the fulcrum,
and L2 the distance from F2 to the fulcrum. If L1 is much larger
than L2, then F2 must be much larger than F1 for the equation to
hold. Take an example. Say L2 is 1 m and L2 is 10 cm (0.1 m). If
F1 is 50 N, then F2 must be 500 N, since (50 N)(1 m) = (500 N)(.1 m).
Output forces can be less or greater than the input force. For exa-
mple, take the old mechanical typewriters. Since what you want is
motion -- for the type to move in an arc to strike the paper -- you
use a greater force with a small motion (pressing on the keys) to get
less force with a greater motion. This is like working a crowbar
backwards from its ordinary use.
11. Kinetic energy goes as the square of the speed. So the effect is as
follows:
- doubled: 2 squared is 4 -- KE increases 4 times
- tripled: 3 squared is 9 -- KE increases 9 times
- quadrupled: 4 squared is 16 -- KE increases 16 times
Example: Increase the speed of a 2 kg object from 2 m/s to 6 m/s
(i.e., triple it).
- original KE = (.5)(2 kg)(2 m/s)(2 m/s) = 4 J
- new KE = (.5)(2 kg)(6 m/s)(6 m/s) = 36 J ( = 9 x 4 J)
14. It should collapse, as we discussed in class. When the car col-
lapses (but not the passenger compartment!), the passengers are
cushioned somewhat from the forces of collision. Since force and
acceleration are proportional, a minimum acceleration of the
passenger compartment means that the forces acting on the passengers
are also minimized. (This doesn't mean they are small, just not as
large as they otherwise might be.)
REVIEW FOR TEST 2, CHAPTERS 5-8
Review Questions - You should review all questions at the end of each
chapter. However, particular attention should be payed to the follow-
ing ones.
A good way to study using this sheet is to read the question from the
book and try to answer it. Then check your answer with what is given
below.
Questions covered in this review:
Ch 5 -- 1, 2, 4 - 8
Ch 6 -- 1 - 7, 9 - 11, 13
Ch 7 -- 1 - 7
Ch 8 -- 1 - 3
Chapter 5
1. The answer to this question comes from the formula for hydrostatic
pressure, p = dgh. The hydrostatic pressure p depends ONLY upon
the density of the liquid d, the acceleration of gravity g, and the
depth beneath the surface h. It does not depend upon volume or
shape of container. Nor does it depend upon total weight of the
liquid. (Note that "weight density" is given by dg in the formula
p = dgh, so p DOES depend upon weight density, because weight den-
sity, in turn depends upon mass density d and acceleration of gravity
g.)
2. Archimedes' principle states that the buoyant force that arises when
an object is immersed in a fluid equals the weight of the displaced
fluid. This leads to the consequence that an object with a density
greater (less than) that of the fluid will sink (float). If the
densities are the same you have a situation of neutral buoyancy and
the object will remain motionless wherever it is placed in a still
fluid. The hydrometer is a device based upon Archimedes' principle.
It will float in many liquids because its overall density is less
than those liquids. However, it will float lower in a less dense
liquid and higher in a denser liquid. A scale on the side of the
hydrometer will then give the density of the liquid, usually as the
specific gravity.
Be familiar with the term "specific gravity". This is the density
of a substance relative to pure water. Therefore it is a unitless
ratio. A specific gravity less than one is less dense than water.
A specific gravity greater than one is denser than water. Because
the density of water is 1 gram per cubic centimeter, the specific
gravity has the NUMERICAL value of density in grams per cubic
centimeter but without the units.
4. The bottle is elevated to increase the hydrostatic pressure (the "h"
in the formula p = dgh). The flow rate is proportional to the pres-
sure and the pressure in this case is proportional to the height of
the liquid (p = dgh). Therefore the flow rate is proportional to
the height and the flow rate would be doubled if the height is doubled.
5. The answer to this question comes from examining the Poiseuille
formula for flow rate through a tube. The flow rate depends directly
on the pressure and inversely on both the viscosity and the length
of the tube. The flow rate depends on the FOURTH POWER of the ra-
dius of the tube. Because of this fourth power dependence, the ra-
dius has a tremendous effect on the flow rate. If you double each
of the parameters mentioned above independently, you will double the
flow rate due to the pressure and halve the flow rate due to either
viscosity or length. However, doubling the radius all by itself
increases the flow rate by a factor of 2 to the 4, or 16 times.
6. Poiseuille's law QUALITATIVELY describes the flow of fluid when
turbulence is not a factor. That is, it tells you how the flow
rate depends on the parameters of pressure, length, viscosity, and
radius. It gives accurate numerical results only for very smooth
flow of a newtonian fluid. (Fluids that don't obey Poiseuille's law
are called non-newtonian.) In the blood the flow through the capil-
laries is non-newtonian due to the effect of the relatively large
size of the blood cells compared to the capillary openings. Another
place where Poiseuille's law does poorly is for rapid flow (due to
exercise, say) in large arteries where there may be some turbulence.
Between those two extremes, Poiseuille's law gives at least a good
qualitative picture of the flow of the blood.
Also remember that the Reynolds number provides a means to predict
whether or not you will get turbulent flow in a fluid.
7. An aneurysm can disturb the flow, even though it is a widening of an
artery, increasing the possibility of turbulence. Turbulence in a
flow can greatly increase the resistance to flow. Therefore, if
turbulence exists in an artery, the heart will have to work harder
to overcome the resistance, raising the blood pressure.
8. See also the answer to no. 5. In particular, if you double the
length, the flow rate will be halved, since flow rate is inversely
proportional to length. If you halve the viscosity, you will double
the flow rate, since flow rate is inversely proportional to viscosity.
If you quadruple the pressure, you will quadruple the flow rate,
since flow rate is directly proportional to pressure. Finally, if
you halve the radius, the flow rate will change by a factor of 1/2
raised to the fourth power, or 1/16. So the flow rate will be one-
sixteenth of its previous value.
Chapter 6
1. Most substances expand when warmed and become less dense. Warm air
will rise because it is less dense than the surrounding air. So
Archimedes' principle becomes involved, the warm air experiences a
buoyant force, and up it goes. This is the cause of thermals on a
sunny afternoon, and is partially responsible for the generation of
thunderstorms and other convective phenomena.
2. As the bubble rises there is less and less liquid above it, meaning
that the pressure the bubble experiences drops. From the equation
of state of an ideal gas (pV = nRT), if the pressure drops and the
temperature remains constant the volume should grow. (The tempera-
ture of the air in the bubble should remain close to that of the
water, since it is in intimate contact with the water.)
3. Atmospheric pressure holds the liquid in the dropper. When you turn
the dropper so that it points downward, a partial vacuum is created
in the bulb as the liquid begins to move out. This motion is quickly
halted by the increase in pressure between the atmosphere and the
partial vacuum in the bulb.
4. Look at pV = nRT. Although the can will expand somewhat with tem-
perature, its volume will be approximately constant. Therefore the
rising temperature in the gas of the can will cause an increase in
pressure. With V and n constant, as T rises p must also rise for the
equation of state to hold.
5. See also question 3. A partial vacuum will be created at the closed
end of the bottle. The liquid will therefore not come out unless air
can enter the bottle and rise to the top, relieving the partial
vacuum. This is why the liquid glug-glug-glugs out of the bottle as
air bubbles enter the mouth and rise.
6. It is NOT the suction of the partial vacuum!! The partial vacuum
created by sucking sets up a pressure difference between the surface
of the liquid in the glass and the partial vacuum in the straw. The
liquid is PUSHED up the straw by this pressure differential.
7. By Pascal's principle that pressure is transmitted equally to all
parts of your body. This means there is no pressure DIFFERENCE in
your body. If you rise or descend in the atmosphere quickly enough,
however, there will be a pressure difference that you can feel, in
your inner ear, for example.
9. Absolute pressure is measured with respect to the vacuum and cannot
be negative. Negative pressure can only occur in gauge pressure,
which is pressure measured with respect to ambient pressure (usually
atmospheric pressure). A negative gauge pressure means the absolute
pressure measured in a container is less than pressure outside the
container, such as if there were a partial vacuum in the container.
10. The pressure in the thoracic cavity is less than atmospheric at all
times to maintain the inflation of the lungs. If the thoracic cavity
were punctured and opened to atmospheric pressure, one of the lungs
would collapse. (Or both lungs, if both sides were opened.)
11. The lungs are elastic and can force the air out like a balloon. A
balloon that is blown up and then the spout opened will expel the
air inside due to the wall tension of the balloon, which creates a
pressure inside the balloon greater than one atmosphere. Similarly,
the alveoli of the lungs have a surface tension that forces air out
of them during exhalation, when the negative pressure of the thoracic
cavity is lessened.
13. Mercury is much more dense (13.6 times) than water. Therefore it
takes a smaller column of mercury to measure the same pressure. A
water manometer would be unwieldy for many applications, because
it would have to be 13.6 times longer than a mercury manometer.
ADDENDUM: In addition to the above questions, you should understand
the quantities in the equation of state of an ideal gas, pV = nRT.
Remember that p is the ABSOLUTE pressure and T is the ABSOLUTE (kel-
vin) temperature. V is the volume of the gas and n the number of
moles.
Chapter 7
1. From the formula flow rate = area x average speed, we see that if
the area involved in the flow increases the average speed will drop.
Although each individual capillary is very small, the sum of the
cross-sectional areas of all the capillaries is much larger than that
of the arteries that feed the capillaries. So the flow of blood
actually slows down in the capillaries.
2. Since liquids are incompressible, the volume flow rate must be the
same at all stages in a closed circulation system. This is because
you can't (easily) change the volume of the liquid, by either com-
pressing it or expanding it. If the flow rate at one stage were
larger, say, than at the next, then the liquid would have to be
undergoing compression when moving between those stages. This can
happen to a gas but not to a liquid (to any significant degree).
3. Blood flowing downward is helped by the pull of gravity, but is im-
peded when flowing upward. Related to this is the fact that, even if
blood were not flowing, the pressure would be greater in the feet
than in the head due to hydrostatic pressure (dgh). So it is easier
to maintain blood pressure in the lower parts of the body than in
the higher parts.
4. The blood vessels in the muscles dilate, allowing increased blood
flow there. Recall the effect of the radius of a tube on the flow
of fluid through the tube. Since the volume of blood remains the
same, this means blood vessels in other parts of the body must con-
tract. If this dilation/contraction didn't occur, the heart would
have to produce a larger volume flow rate than it actually does to
get sufficient blood to the muscles.
5. From Poiseuille's law we know that the variables are pressure, ra-
dius, viscosity, and length. The length of the artery is obviously
fixed, and the viscosity of the blood varies only a little and
usually relatively slowly. So only the pressure and the radius of
the artery can significantly affect the blood flow rate. As we have
seen earlier, it is the radius that is most effective in controlling
the flow rate, since its effect goes according to the fourth power.
6. The resistance of the capillaries to blood flow smooths out the
variations in pressure as the heart pumps. That is, the pressure
variations seen in the arteries are largely expressed across the
capillaries. By the time the blood gets into the veins, there is
little left of these pressure variations.
7. The elasticity of the arterial walls maintains a certain amount of
blood pressure even when the heart is not forcing blood into the
artery. This is the diastolic pressure. The peak pressure due to
the action of the heart is the systolic pressure.
Chapter 8
1. Because of the incompressibility of liquid, the volume flow rate is
the same in the constricted area as in the unconstricted area.
However, the formula flow rate = cross-sectional area x average
speed, shows that the speed of the flow must increase as the area
decreases in order to maintain a constant flow rate. By the Ber-
noulli principle the pressure will decrease as the velocity of the
liquid increases. (Note the authors use "fluid" instead of "liquid"
here. They should have used liquid, because gas is a fluid, and the
flow rate does not have to remain constant in a closed circulatory
system involving a gas under certain circumstances, since gas is
compressible.)
2. A constricted area in a tube used for entrainment is called a
venturi. In a venturi the pressure drops due to the faster speed
of the flow. If there is another tube entering into the venturi
from the side, the lower pressure in the venturi can cause fluid
from the side tube to be pushed into the venturi due to the higher
pressure in this fluid. This is called entrainment.
3. Examples: atomizer, aspirator, nebulizer.
ADDENDUM: Be sure to understand the Coanda effect as used in respira-
tory applications. Recall that the Bernoulli effect causes air to
follow contours when those contours are opened to the atmosphere.
This can be exploited to direct air flow in respirator valves like
the one described in class.
REVIEW FOR TEST 3, CHAPTERS 9-15
Review Questions - You should review all questions at the end of each
chapter. However, particular attention should be payed to the follow-
ing ones.
A good way to study using this sheet is to read the question from the
book and try to answer it. Then check your answer with what is given
below.
Questions covered in this review:
Ch 9 -- 1 - 7, 9, 11
Ch 10 -- 1 - 5, 7, 9 - 12
Ch 11 -- 1, 2, 4 - 9, 11 - 15, 17, 18
Ch 12 -- 1 - 7, 10, 11
Ch 13 -- 1 - 7
Ch 14 -- 1 - 3, 5 - 7
Ch 15 -- Be familiar with the terms sensor, amplifier, and display
device.
Chapter 9
1. Random thermal motion of individual molecules can result in a NET
motion if the concentration of the molecules changes from one point
to another. More molecules will move, on average, from higher to
lower concentration than will move, on average, from lower to higher
concentration. This process is called diffusion. When the concen-
tration is different on either side of a membrane for a molecule that
can get through the membrane, the net flow will be from the side with
the higher concentration to the side with the lower concentration.
2. By raising the temperature you increase the magnitude of the random
thermal motion of the molecules in the water. This mechanical
agitation results in faster dissolution of the solid material due
to faster water molecules colliding with the molecules of the solid.
3. Osmosis refers to the process whereby the solvent in a solution can
pass through a membrane but the solute cannot. Dialysis occurs
when smaller solute molecules can pass through a membrane in addition
to the solvent molecules, leaving the larger solute molecules behind.
4. Both depend on the random thermal motion of molecules resulting in a
net molecular motion from higher to lower concentration.
5. Osmotic pressure can be defined as the hydrostatic pressure that
would be necessary to prevent a net amount of solvent from crossing
the membrane. Solvent migrates toward the higher osmotic pressure.
6. Isotonic: Refers to two fluids in which the concentration of the
solute is equal.
Hypotonic: Refers to the fluid with the smaller concentration of
solute.
Hypertonic: Refers to the fluid with the larger concentration of
solute.
7. A cell finding itself in a hypotonic solution would take on water
and swell. A cell finding itself in a hypertonic solution would give
up water and shrink. Both effects are due to net diffusion of the
solvent from higher to lower concentration.
9. The surface tension of water is high. For a drop of water this
surface tension tends to draw the drop up into the smallest possible
surface area for the given volume of water, which is a sphere.
11. The large surface tension of water allows relatively large water
droplets to form in the same way a stronger bag can handle a heavier
load.
ADDENDUM: Don't forget that water has an extremely high surface
tension. This means that, in the lungs, water is NOT good as a
coating for the alveoli. A surfactant is a substance that lowers
the surface tension. The fluid lining the alveoli contains a surfac-
tant that reduces the surface tension, preventing collapse of the
alveoli. Remarkably, this substance adjusts its surface tension
as the alveoli change shape in order to maintain the equilibrium of
the alveoli.
Chapter 10
1. By definition internal energy excludes energy of objects involving
any shared energy of the molecules as a whole. For example, the
kinetic energy of a baseball due to its motion as a projectile is
not internal energy. The potential energy of an object lifted to
a higher position is also not internal energy, since this change of
position is shared by all the molecules equally. Internal energy
is the energy the molecules have that is NOT shared as a whole, i.e.,
random kinetic and potential (electrical) energy.
2. No. The internal energy of a substance depends on details of its
molecular and electronic properties, which are reflected, for example,
in the different specific heats of different substances.
3. Skin is sensitive to heat flow, not temperature per se. Therefore,
since heat conducts more readily through a metal than through wood,
the spade of a shovel left outside in the winter will feel colder
than the handle, even though they are at the same temperature.
4. The hole will get bigger, because all parts of the object expand.
5. A bimetallic strip is made of two strips of different metals bonded
together, where one metal has a higher coefficient of expansion than
the other. The differential expansion/contraction of the two strips
with changing temperature bends the bimetallic strip. The amount of
this bending can be used to make a thermometer.
7. The glass has a higher coefficient of expansion than the rubber, and
the opening in the bottle will expand more than the stopper. In
addition, the hot water can be directed at the glass more than the
rubber, creating a temperature difference that will enhance the
difference in expansion.
9. Water has a very high specific heat. Therefore you can get a larger
flow of heat from warm water than from almost any other substance.
(Further, water is ubiquitous and safe.)
10. The high specific heat of water means that an object with a high
water content can take on or give up a lot of heat without changing
its temperature as much as would otherwise occur. Since the human
body contains a lot of water, this helps regulate our temperature.
ll. A large body of water is a source of heat in cool weather and a sink
for excess heat in hot weather. This is, again, due to the high
specific heat of water. Temperature extremes are thus moderated
around large bodies of water.
12. A dietary calorie equals 1000 physical calories.
Chapter 11
1. Water has a high heat of fusion. This means that it takes a lot of
heat to change a gram of ice at 0 deg C to a gram of water at 0 deg
C (80 calories). Hence the ice will absorb 80 calories per gram
before turning into 0 deg C water.
2. No. The temperature of boiling water is 100 deg C, whether the water
is boiling rapidly or slowly.
4. They occur at a particular temperature and pressure and are readily
reproducible in a laboratory.
5. It takes heat to evaporate water. Evaporation is basically the
process where the faster molecules leave the slower ones behind.
The slower the molecules, the colder the liquid. If enough fast
molecules leave, the remaining molecules may be cold enough to
freeze.
6. The boiling point falls as pressure is reduced. Hence water boils
at a reduced temperature at high altitude, slowing the cooking of
food. The pressure in a pressure cooker, because it is closed, will
be higher than ambient pressure. Therefore the water will be boiling
at a higher temperature.
7. Two: the temperature of the liquid (faster molecules escape more
easily) and the vapor pressure above the liquid (the higher the
vapor pressure, the more molecules that will strike the surface
and can be captured back into the liquid state). The higher the
temperature and the lower the vapor pressure, the faster the
evaporation.
8. The molecules in air move faster when warm than when cold. This
causes the air to expand allowing more room for water vapor to
occupy up to the point where no more water can squeeze in. Thus the
saturation vapor pressure is higher for warmer air.
9. The relative humidity will decrease. As the air heats up the satura-
tion vapor density rises. However, in a closed room the amount of
water vapor, and hence the actual vapor density, remains constant.
Since relative humidity is the measure of actual to saturation
vapor density, it goes down.
11. The dew point is the temperature at which the air is saturated with
water vapor. The air in contact with a cold pitcher of water is
cooled. When the air is cooled down to its dew point, the relative
humidity is 100% and the air can hold no more water. As the air is
cooled further, some of this water has to leave the air and condense
on the pitcher.
12. The temperature of boiling water cannot rise above 100 deg C at a
pressure of 1 atm, whereas steam can be raised to any temperature.
13. Conduction, convection, radiation, perspiration. Only perspiration
can cool the body when ambient temperature is higher than body
temperature. In the first three methods heat always flows from high
to low temperature. Because perspiration involves the evaporation of
water, heat can be taken from the body by the evaporating water even
when ambient temperature is higher than body temperature.
14. Metal has a higher heat conductivity. So it will transmit heat from
the coffee into the air more efficiently.
15. No. Heat flow is inhibited by insulation no matter which way it
goes, whether from a hotter outside to a cooler inside or from a
hotter inside to a cooler outside.
17. No. The electric fan uses electrical energy which will ultimately
turn into heat. (The fan heats up.) The fan is only effective in
that it stirs cooler air around the body and can also enhance
perspiration by replacing saturated air near the skin with drier
air. In other words, you gotta be in the room for it to work.
18. To reflect infrared (heat) radiation back into the contents of the
flask, reducing heat loss through radiation.
Chapter 12
1. The electrical force is very strong, so a charged atom will tend to
quickly pick up an electron (if it has lost one or more) or give up
an electron (if it has an excess). Hence atoms tend to be neutral
except where the temperature is so hot that the electrons are
stripped from the atoms by violent collisions (as in stars).
2. Atom: nucleus of protons and neutrons surrounded by a "cloud" of
electrons.
Ion: an atom with a deficit or excess of electrons.
Molecule: a chemical combination of two or more atoms.
3. The electrical force goes as an inverse square law. "Inverse" means
the force decreases with distance. "Square" means the force changes
as the square. So if the distance is doubled, the force decreases by
a factor of four. If the distance is halved, the force increases by
a factor of four, etc.
4. Look at the equation for Coulomb's law to answer this.
Q1 Q2
F = k --------
r^2
a. If you double one charge, Q1 say, the force will be doubled.
b. If you halve the distance, the force will increase by four.
c. If you change the polarity of one charge, the force will reverse
direction.
d. If you change the polarities of both charges, the force is un-
changed.
5. Like charges repel, so the charge (consisting of electrons) will
as a whole "repel itself", and try to spread out. The path it can
follow is to the earth along the conducting ground wire, so that's
where it goes.
6. One ampere = the flow of one coulomb of charge per second.
One volt = the potential to provide one joule of energy for each
coulomb of charge transferred. The volt is proportional to electri-
cal energy. (Also be familiar with milliamp and millivolt.)
7. Electrons. The positive nuclei are too solidly bound to move much.
10. Battery, coil of wire, iron core. Practically speaking, no, although
nickel and cobalt are ferromagnetic to some extent.
(Also know what "ferromagnetic" means. A ferromagnetic material has
domains of d-shell electrons aligned parallel to each other. Recall
electrons are like little magnets. When these domains are lined up,
the ferromagnetic material is magnetized.)
11. A charge must be moving through a magnetic field to experience a
force (called the Lorentz force). The faster the charge the greater
the Lorentz force. The more closely the charge moves perpendicularly
to the magnetic field, the greater the force.
Chapter 13
1. The analogs are as follows: voltage = pump, current = water flow,
resistance = narrow pipe.
2. A short circuit is where the current follows a path shorter than
that intended. If the short is to an accessible part of the device,
it can cause electrocution. It can also cause heating and fire.
At the least it can cause the malfunction of a piece of equipment,
which, in a hospital, may be critical, even life-threatening.
3. An open circuit is where the current can't flow due to a break in
the circuit. Malfunction (or total lack of use) of equipment is
one consequence. If the broken circuit results in exposure of a
wire or other electrified item, it can cause electric shock.
4. The bird is at the same potential as the wire. There is nothing to
complete the circuit, so no current flows.
5. A fuse or circuit breaker will open the circuit if too much current
is drawn. The hazards are basically the same as with the short
circuit (no. 2).
6. A ground wire is to keep the "chassis" of the electrical device at
the same potential as the ground. This should prevent a voltage
difference across someone touching the chassis. With no ground
wire a short circuit to the chassis could cause electrocution.
However, a ground wire may not prevent fire hazard. This is one
function of the fuse, so both ground wire and fuse are required for
greatest safety.
7. A DC current is where the charge flows in one direction, as from a
battery. An AC current is where the charge oscillates back and forth
in the wire, as in common house current. DC can be used to light
bulbs, run DC motors, and operate various DC electrical devices.
AC runs AC motors, lights bulbs, runs AC powered electrical devices.
Chapter 14
1. Current.
2. The amount of current that flows depends both on the voltage and the
resistance to current flow through Ohm's law: I = V/R.
3. The muscles contract and lose the ability to respond to the brain.
That is because the brain communicates with the muscles electrically.
5. They also use high frequencies. The higher the frequency, the less
the penetration of current into a conducting substance. Hence the
current stays near the surface and does not interfere with internal
organs, such as the heart.
6. Like the bird on a wire, there is an incomplete circuit. There must
be a complete circuit for charge to flow.
7. Any opening of the skin can make a patient microshock sensitive.
This is because the skin, if dry, has a high resistance. Break the
skin and you expose the patient's highly conducting flesh.
Chapter 15
Know the following:
Sensor: detects a signal (pressure, temperature, etc) and turns it
into a voltage.
Amplifier: amplifies the current produced by the sensor's voltage.
Display device: converts the amplified voltage signal into a
display, such as analog (e.g., a meter) or digital (e.g., numbers).
May also be a graphical display, such as a graph or plot.
REVIEW FOR TEST 4, CHAPTERS 16-19
Review Questions - You should review all questions at the end of each
chapter. However, particular attention should be payed to the follow-
ing ones.
A good way to study using this sheet is to read the question from the
book and try to answer it. Then check your answer with what is given
below.
Questions covered in this review:
Ch 16 -- 1 - 4
Ch 17 -- 1 - 6
Ch 18 -- 1, 4 - 9
Ch 19 -- 1 - 9, 11
Chapter 16
1. Both the electrical force and the concentration gradient act in the
same direction for sodium, causing a net amount of sodium to enter
the cell whenever the membrane is permeable to sodium. On the other
hand, the eletrical force and concentration gradient are opposed for
potassium and chlorine. This is because diffusion of potassium
across the cell membrane to the outside of the cell creates a charge
separation that opposes the diffusion of potassium. Chlorine, being
a negative ion, is repelled by the negative cell interior created by
the diffusion of potassium, even though diffusion would tend to move
chlorine into the cell. Positive sodium, which is concentrated out-
side the cell is attracted to the negative cell interior.
2. The flow of Na+ into the cell reduces the potential difference across
the cell membrane that was inhibiting the flow of K+ from inside the
cell to the outside, allowing K+ to diffuse across the cell membrane
to the outside of the cell.
3. Depolarization is the process whereby the voltage difference across
the cell membrane is decreased due to the flow of Na+ into the cell.
Repolarization occurs when K+ flows out of the cell, reestablishing
the potential difference. The action potential is the voltage pulse
produced by the depolarization-repolarization process.
4. It takes a few milliseconds for the repolarization process to be
completed so that sufficient electrical energy is again stored in
the cell membrane for a "firing" to occur.
Chapter 17
1. It is helpful to think of a mass-spring system when considering this
question. There is zero force acting on the mass at the equilibrium
position. Therefore if the mass is moving through that position
(for example, after stretching the spring and releasing the mass),
there is no force to bring it to a stop, so it just keeps on moving.
As the spring is compressed (or stretched) after the mass passes
through equilibrium, the restoring force starts to slow the mass
down, eventually bringing to a stop, then moving it back toward the
equilibrium point. The mass goes through that point again and the
restoring force acts again to slow it down and reverse its direction
of motion. The key to answering this question is to recognize that
at equilibrium there is no force acting on an elastic medium so the
medium just continues moving when it passes through that point.
2. Beats between close frequencies, standing waves in strings and tubes,
rainbow of colors seen in films (such as soap films).
3. No, sound involves the vibration of atoms and/or molecules in solids,
liquids, and gases.
4. No, at least, not for "linear waves". The speed of propagation is
the same for all frequencies of linear waves. Examples are sound,
waves in strings, and light. For nonlinear waves the speed does
vary with frequency, for example, waves on the surface of a liquid.
This is why long-wavelength tsunami waves can travel across an ocean
in hours, wreaking destruction on shorelines thousands of miles from
the earthquake that caused it.
5. In a longitudinal wave the vibration is parallel to the direction
of propagation of the wave. In a transverse wave the vibration is
perpendicular to the direction of propagation. Longitudinal: sound,
P seismic waves. Transverse: waves in strings, light, water waves,
S seismic waves.
6. A sustained sound is caused by a standing wave. This is where a wave
is reflected back onto itself in such a way that there are points of
maximum vibration (constructive interference) and minimum vibration
(destructive interference) which are stationary. These standing
waves define the natural frequencies of vibration of the object in
which they are produced (e.g., an organ pipe). They can be produced
by causing an object to vibrate at one of its natural frequencies.
This is called resonance.
ALSO. Remember that intensity is defined as the power of the wave
incident on a unit area and has the units in SI of watts per
square meter (although it is often measured in watts per square
centimeter).
Chapter 18
1. Sound is the propagation of atomic/molecular vibrations through gas,
liquid, or solid. When a tuning fork vibrates it compresses and
rarifies the air in its vicinity as its tines move back and forth.
These disturbances propagate through the air as vibrations -- sound.
4. Speech heard from people at a distance would be unintelligible,
because the mix of frequencies is what contains the information in
speech. If the frequencies traveled at different speeds, they would
be out of phase after a certain distance traveled. Music would also
sound like noise at a distance from, say, a band, since the different
frequencies would arrive at different times.
5. Loudness is based on how the human ear responds to sound. Intensity
is just the power per unit area. An intense sound that is beyond
the range of human hearing is not loud because you can't hear it.
6. The range of sound intensity is very large, over many powers of ten.
The decibel scale is designed to condense this large range into a
smaller range of more manageable numbers by using the logarithm of
the intensity rather than the intensity itself.
7. Sound at frequencies too high to be heard (ultrasound) or too low to
be heard (infrasound) can be extremely intense but will not be picked
up by the ear.
8. [Note that the sequence in this question should be 125, 250, 500,
and so on -- there is a misprint.] Because human hearing is respon-
sive to ratios of frequencies, which is the basis of music.
9. Since they cannot hear the higher frequencies very well, they do not
have the ability to distinguish the meaning contained in quality of
sound, which is a function of the frequency mixture, high as well as
low.
ALSO. Don't forget that each increase of 10 decibels corresponds to a
tenfold increase in the intensity.
Chapter 19
1. Refraction of light coming out of the water into the air produces a
lensing effect which enlarges the image of the object, making it
appear closer.
2. No. In the case of the shore fisherman, the light bends by refrac-
tion as it emerges from water into the air. However, since the
skin diver is under the water, there is no water-air interface to
produce refraction.
3. An object placed outside the focal length of a converging lens will
form a real, inverted image that is diminished.
4. Light traveling parallel to the lens axis and striking a positive
(converging) lens will be focused to the focal point of the lens.
Light traveling parallel to the lens axis and striking a negative
(diverging) lens lens will be focused away from the focal point of
the lens.
5. The lens must thicken, shortening its focal length in order to
better focus a close object on the retina.
6. The lens may become less flexible, limiting its range of focus.
This may require bifocals with "reading" lenses at the bottom of
the glasses. These lenses have shorter focal lengths to help
viewing close objects.
7. A myopic eye is near sighted. The eye lens has too short a focal
length to focus distant objects on the retina. Instead, they are
focused in front of the retina. The correction consists of appro-
priate diverging lenses.
8. A hyperopic eye is far sighted. The eye lens has too long a focal
length to focus near objects on the retina. Instead, they are
focused in back of the retina. The correction consists of appro-
priate converging lenses.
9. Astigmatism occurs when the eye lens is distorted and no longer
symmetrical. In effect the lens has more than one focal length,
depending on which side of the lens the light strikes. Lenses
that are distorted opposite to the eye lens are necessary for
correction.
11. Red light has a longer wavelength and lower frequency than blue.
ALSO. A converging lens produces a real, inverted, diminished image
if the object is beyond the focal point. A converging lens produces
a virtual, erect, magnified image if the object is inside the
focal point. A diverging lens always produces a virtual, erect
image, whether the object is inside or outside the focal length.
A real image can be projected on a screen and a virtual image can
not. A virtual image can be seen with the eye, however.