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PowerPoint® Lectures for

College Physics: A Strategic Approach, Second Edition

Chapter 27

Relativity

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27 Relativity

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Reading Quiz

Which of these topics was not discussed in this

chapter?

A. Teleportation

B. Simultaneity

C. Time dilation

D. Length contraction

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Answer

Which of these topics was not discussed in this

chapter?

A. Teleportation

B. Simultaneity

C. Time dilation

D. Length contraction

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Two Standard Reference Frames

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Inertial Reference Frames

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Which of these is an inertial reference frame (or a very good approximation)?

A. Your bedroom

B. A car rolling down a steep hill

C. A train coasting along a level track

D. A rocket being launched

E. A roller coaster going over the top of a hill

F. A sky diver falling at terminal speed.

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Which of these is an inertial reference frame (or a very good approximation)?

A. Your bedroom

B. A car rolling down a steep hill

C. A train coasting along a level track

D. A rocket being launched

E. A roller coaster going over the top of a hill

F. A sky diver falling at terminal speed.

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The Galilean Velocity Transformations A motorcycle’s velocity as seen by Sue and Jim

Jim sees

25 mph

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Ocean waves are approaching the beach at 10

m/s. A boat heading out to sea travels at 6 m/s.

How fast are the waves moving in the boat’s

reference frame?

A. 16 m/s

B. 10 m/s

C. 6 m/s

D. 4 m/s

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Ocean waves are approaching the beach at 10

m/s. A boat heading out to sea travels at 6 m/s.

How fast are the waves moving in the boat’s

reference frame?

A. 16 m/s

B. 10 m/s

C. 6 m/s

D. 4 m/s

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Einstein wondered: How would light look if you surfed along with it?

Logical problem: Light depends on an electric field creating a magnetic field and a changing magnetic field creating an electric field.

If you move with it, the fields don’t change!

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Principle of Relativity: All the laws of physics are the same in all inertial reference frames.

1. Maxwell’s equations are true in all inertial reference frames.

2. Maxwell’s equations predict that electromagnetic waves, including light, travel at speed c = 3.00 x 108 m/s.

3. Therefore, light travels at speed c in all inertial reference frames.

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The Constancy of the Speed of Light

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All experimental evidence supports this theory!

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A carpenter is working ona house two blocks away. You notice a slight delay between seing the hamer hit the nail and hearing the blow. At what time does the event “hammer hits nail” occur?

A. At the instant you hear the blow

B. At the instant you see the hammer hit

C. Very slight before you see the hammer hit

D. Very slight after you see the hammer hit

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A carpenter is working on a house two blocks away. You notice a slight delay between seeing the hammer hit the nail and hearing the blow. At what time does the event “hammer hits nail” occur?

A. At the instant you hear the blow

B. At the instant you see the hammer hit

C. Very slightly before you see the hammer hit

D. Very slightly after you see the hammer hit

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Time Dilation: a Light Clock

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Analysis of a Moving Clock

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Analysis of a Moving Clock

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Time Dilation and Proper Time

“Moving clocks run slower”

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The Twin Paradox

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Length Contraction

Helen measures a shorter distance than George. An object’s length is contracted only in the direction in which it’s moving.

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Relativistic Energy

The total energy is made up of two contributions:

2 2( 1)E mc mc g2 2( 1)E mc mc g2 2( 1)E mc mc g

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Conservation of Energy in Relativity

235 236 144 89n + U U Ba + Kr +3n