Chapter 7 Review

Video Review

Key Concept Summary

TA Summary

Vocabulary

An object or location that is experiencing no acceleration

An object or location that is undergoing an acceleration

The observation that the laws of nature are the same for all intertial frames of reference

The theory that considers non-inertial frames of reference

The notion that separate speed vectors can be added together in a "straight-forward" way to form a total velocity vector

The idea that motion is only defined relative to other objects, which may have their own motion

The theory that describes how nature behaves when encountering high speeds

A thought experiment contrived to illustrate a particular effect

True/False

The laws of nature remain the same for any inertial frame of reference.

True False

We call any object moving without acceleration an inertial frame of reference.

True False

A laboratory on Earth's surface is a true inertial frame of reference.

True False

Motion symmetry only works for inertial frames of reference.

True False

"Absolute motion" only exists in outer space.

True False

According to Einstein, absolute space and time don't exist.

True False

Light does not obey Galilean Relativity.

True False

The speed of light in a vacuum has a constant value.

True False

The faster a clock moves, the faster its time runs.

True False

An astronaut in a spaceship moving near the speed of light will observe all of the objects within the spaceship to be shorter than they were before the spaceship took off.

True False

Analysis

Non-intertial frames of reference

have no unbalanced forces acting on them. feel an unbalanced force. accelerate. both the second and third choices

Which of the following is in accelerated motion?

a spaceship that isn't experiencing a net force a merry-go-round that is spinning at a constant rate a hippopotamus sliding straight acress a frictionless surface none of the above

You are traveling in a straight line down the freeway with your cruise control set at 55 mph. Assuming you can choose any reference point you please, which of the following viewpoints(s) would be scientifically legitimate?

you are at rest you are moving forward at 55 mph the freeway is moving backward at 55 mph you are speeding up from 0 to 55 all of the above only the first three above

How does the chapter define "high speed?"

faster than the speed of sound faster than a speeding bullet faster than the speed of light Slightly slower than the speed of light

In what direction do moving objects contract?

in all directions in the direction perpendicular to the direction of motion in the direction of motion Moving objects expand, not contract.

From the scientists' reference frame, the muon experiment demonstrated

time dilation length contraction mass increase simultaneity

Which of the following statements is true?

Moving objects are shorter than when they are at rest. Moving clocks run fast. Two events that are simultaneous on one reference frame are always simultaneous in another reference frame. Non-inertial reference frames do not exist.

The light clock experiment is a thought experiment that illustrates

length expansion. time dilation. mass increase. anomalous dispersion. motion symmetry.

A train moving near the speed of light enters a tunnel. According to a person standing in the middle of the tunnel, the back end of the train enters the tunnel just as the front end is emerging. What happens according to someone sitting in the middle of the train?

The back end enters the tunnel at the same time as the front end emerges. The back end enters the tunnel before the front end emerges. The front end leaves the tunnel before the back end enters. The front end leaves the tunnel at the same time the back end passes the person standing in the middle of the tunnel. The front and back ends of the train enter the tunnel at the same time.

A distant star is moving toward the earth at a speed of 1/4 the speed of light. Compared to the light from a flashlight on the earth, the speed of the light from the star would be

1/4 as fast. 3/4 as fast. the same. 1 1/4 times as fast. 1 3/4 times as fast.

You are in a spaceship moving in a straight line at constant speed. You cannot see out of the ship. Assuming perfectly uniform motion, which of the following is true? (Select all correct answers.)

You could determine that you are moving by measuring changes in the motion of a ball thrown parallel to the direction you are traveling. You could determine that you are moving by measuring changes in the motion of a ball thrown perpendicular to the direction you are traveling. You could determine that you are moving by measuring the change in length of the ship you are in. There is no experiment you can do to determine that you are moving.

A man standing on the ground sees two lightning flashes simultaneously, 1 kilometer to the east and 1 kilometer to the west of where he is standing. Since he sees the light simultaneously, and it travels equal distances, he concludes that the lightning hits the ground at exactly the same time in the two locations. What happens according to a man driving by, east to west, very close to the speed of light? A depiction of the lightning strikes described above.

A depiction of the lightning strikes described above.

According to the driver, the flashes occur and are seen simultaneously. According to the driver, the flashes occur simultaneously, but are seen at two different times. The east flash is seen first, and the west flash is seen last. According to the driver, the flashes occur simultaneously, but are seen at two different times. The west flash is seen first and the east flash is seen last. According to the driver, the flashes occur at different times and the west flash occurs last. According to the driver, the flashes occur at different times and the west flash occurs first.

A frame of reference is inertial if

the reference frame has constant acceleration the reference frame has constant speed the reference frame has constant velocity the reference frame is moving the same way as the objects that are in the reference frame. The refernce frame has mass

Is it possible to prove that the Earth spins on its axis?

yes no

Two people who are moving towards each other shine lights at each other and measure the speed of the light. According to the 2nd postulate of relativity, what will they find?

The light is traveling faster than the speed at rest The light is traveling the same speed as when they're at rest The light is traveling slower than the speed at rest.

For two observers in inertial reference frames that are moving away from each other, the laws of nature are

the same different

Two events that are observed to be simultaneous in one reference frame are simultaneous if observed in another frame if two observers are both in uniform motion.

True False

A clock that is moving close to the speed of light runs _________ than when the clock is stationary.

slower at the same speed faster

The muon decay experiment is a

real experiment gedaken experiment

Challenge Questions

The next 10 questions deal with the following situation: An alien mother ship lands in your backyard to collect examples of Earth life forms. They offer to trade you a flying saucer for your pet cat. You happily accept and are now the proud owner of a 10m diameter flying saucer capable of flying at speeds near the speed of light in the Earth's atmosphere. You immediately take the saucer for a test flight so you can observe relativistic effects first hand. Unless it specifically states otherwise, assume the events in each question take place while you are flying in a straight line at a constant speed near the speed of light.

As you fly along near the speed of light, you measure the diameter of your ship. The measurement you obtain:

is larger than 10m. is equal to 10m. is less than 10m.

You fly over your school's football field to check out what is happening in an ongoing game. You fly from goal post to goal post and measure the distance between the lines. The lines appear:

closer together than 10 yards. 10 yards apart. farther apart than 10 yards.

If the saucer is hovering directly above someone, it appears to be perfectly circular. Which of the answers below best describes the shape people in the football stadium will report seeing as you pass overhead?

a smaller circle, less than 10m in diameter smaller than 10m along the direction it is moving longer than 10m along the direction it is moving exactly the same 10m circle as you'd see if it was sitting still

Still in your flying saucer, moving past the stadium near the speed of light, you glance at the clock on the score board and notice that it is:

running slow. running fast. running at a normal rate.

Your clock says that it is lunch time, so pull up to the drive through window of a fast food restaurant and stop just as your watch hits noon. The clock in the restaurant indicates that it is:

after noon before noon exactly noon.

After lunch you decide to return to the football stadium and see what is happening. Traveling near the speed of light, you fly over the stadium from north to south during the half time show. The people in the stadium see the members of the flag corp raise their flags in unison. You see:

The flag corp raise their flags in unison. The flags ripple up with the flags closest to you going up first. The flags ripple up with the flags on the north going up first. The flags ripple up with the flags on the south going up first.

While your are flying away to the south, someone in the stands decides to try to communicate with you by pointing a laser pointer at you, and wiggling it across your back window 5 times a second. How many light pulses do you see each second?

more than 5 exactly 5 less than 5

If the man in the stands thinks he has flipped the pointer back and forth across the window for a full minute, how long do you think he has been signaling?

more than one minute exactly one minute less than one minute

Suppose you decide to signal the man in the stands back. You return exactly the same signal you received by pointing a laser pointer at him and wiggling it across his shirt. (See the previous two questions.) The man in the stands will see:

more total flashes from you than he sent exactly the same number of flashes he sent fewer total flashes than he sent

When you return the signal you received from the man in the stands, what does the man in the stands see?

more than 5 signals each second exactly 5 signal each second less than 5 signals each second

Free Response

What are the two assumptions of the Special Theory of Relativity?
What are some of the predictions of the Special Theory of Relativity?
What is the difference between the Special and the General Theories of Relativity?
What is a "light clock"?
You are enjoying an enthralling Physical Science lecture in a windowless room when your professor insists that the entire classroom is moving straight toward the Pacific coast at 350 mph.
- Is there any experiment you could perform to prove your professor wrong? Why?
- Now the professor says the classroom is spinning at 60 rpm. Can you prove your professor wrong? Why?
- Name and state the scientific principle on which you based your answers.
A railcar travels at 3/4 the speed of light, and your friend happens to be on it. As you stand on the ground watching your friend pass by, lightning bolts strike both the front and the back of your friend's railcar.
- If he saw the lightning bolts strike the front and the back of the railcar simultaneously, you will disagree. What do you say happened? Why? Note: this is different from the situation in the book.
- To find out who is right, you and your friend meet on the ground and decide to measure the distance between the scorch marks and compare it to your measurement of the length of the car. Are your measurements what you expected it to be? Are your friend's measurements what he expected it to be?
- What does the distance between the scorch marks illustrate about the lengths of moving objects?
- Who was right about the timing of the lightning strikes? What can you conclude about events that are simultaneous in one reference frame?
Your friend is on the railcar again traveling past you at 3/4 the speed of light. You are both holding identical light clocks.
- From your perspective, how does the distance between the mirrors of your friend's light clock compare to the distance between the mirrors of your own?
- How fast is light traveling between your mirrors? How fast is light traveling between your friend's mirrors?
- Based on the distance between the mirrors and the speed at which the light is traveling, what can you conclude about your friend's light clock?
- From your friend's perspective, does the distance between her mirrors appear to be any different than normal? Does time seem to be passing at a different pace than normal?
A disgruntled co-worker impatiently orders you to "get moving". You kindly respond that you are already moving. Support your argument by explaining the relativity of motion.
If the idea of motion symmetry is true, why do some people experience motion sickness? Why is it more common to get seasick than carsick?
Suppose you're in a bus traveling at 60 mph. You throw an orange toward the front of the bus at 20 mph. Then you send a light beam toward the front of the bus at the speed of light.
- From the perspective of a pedestrian observing the bus from the sidewalk, how fast was the orange traveling?
- From the perspective of the same pedestrian, how fast is the light beam moving?
- What can you conclude about the applicability of Galilean relativity?
Even though Newton's laws of motion hold perfectly in everyday life, they become increasingly inaccurate as speeds approach the speed of light. Does this mean that Newton's laws are not "true laws of nature"? What arguments can you make that say they are true laws? Which arguments can you make that say they are not true laws? (Note that at everyday speeds, the laws of motion as stated in the Special Theory of Relativity simplify to Newton's laws of motion.)