Book contents
- Frontmatter
- Contents
- Preface to English edition
- Preface to Japanese edition
- Part I Kinematics: Relativity without any equations
- 1 Welcome to the world of relativity
- 2 Basics
- 3 Galilean relativity
- 4 Einsteinian relativity
- 5 Causality
- 6 Consequences
- 7 Summary of Part I
- Part II Problems
- Part III Dynamics: Relativity with a few equations
- Afterword
- References
- Index
3 - Galilean relativity
Published online by Cambridge University Press: 05 June 2012
- Frontmatter
- Contents
- Preface to English edition
- Preface to Japanese edition
- Part I Kinematics: Relativity without any equations
- 1 Welcome to the world of relativity
- 2 Basics
- 3 Galilean relativity
- 4 Einsteinian relativity
- 5 Causality
- 6 Consequences
- 7 Summary of Part I
- Part II Problems
- Part III Dynamics: Relativity with a few equations
- Afterword
- References
- Index
Summary
Basic questions
Let us recall the basic questions we asked about the motion of an object in section 2.1, namely:
Q1: Is it moving or is it at rest?
Q2+Q3: If it is moving, what is its velocity?
As we have seen, in order to answer these questions we must first choose a frame, and the answers depended on our frame choice.
Let us actually try this out. Consider the car moving along a straight horizontal road as shown in the figure. In the tree-frame, at every instant in time the clock fixed to the tree (though it's not drawn on the tree, assume that it is) will give some reading t (in seconds) and at the same instant the car will be somewhere along the road at some position x (in meters). The figure shows the sequence of this position from time t = 0 seconds to t = 4 seconds in 1-second intervals. As you can see, we can tell from the figure that:
A1: the position of the car is changing with time so it is obviously moving, and
A2+A3: the position of the car is changing at a rate of +1 meters every second so its velocity is +1 meters per second. (The plus sign indicates that the motion is toward the right, so this number tells us not only the speed of the car but also its direction of motion.)
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- Information
- An Illustrated Guide to Relativity , pp. 30 - 58Publisher: Cambridge University PressPrint publication year: 2010