Two rules that rebuilt time

Science · Quantum & Modern Physics · ages 18-19

Name ______________________ Date ____________

Which is an inertial frame?
- A nonrotating frame moving at constant velocity.
- A rotating frame fixed to a moving carousel.
- A braking frame fixed to a slowing road car.
Which pair states both postulates of special relativity?
- Same laws in inertial frames; vacuum light speed is c+v.
- Same laws in inertial frames; vacuum light speed is c.
- Same time in inertial frames; vacuum light speed is c.
Two events simultaneous in one inertial frame must be simultaneous in every inertial frame.
Circle one: True False
In one inertial frame, light from two flashes reaches a stationary detector together through vacuum. The emission-to-detector distances differ. Which flash was emitted earlier in that frame?
- The farther flash was emitted before the nearer flash.
- Both flashes were emitted at the same detector-frame time.
- The nearer flash was emitted before the farther flash.
A train moves toward its front at constant speed. Its midpoint sends light in both directions through vacuum. What is the door illumination order in platform coordinates?
- Front illumination precedes rear illumination.
- Front and rear illumination are simultaneous.
- Rear illumination precedes front illumination.
A train moves at 0.2c relative to a platform and fires a vacuum light pulse forward. What would ordinary velocity addition predict for the pulse's platform speed, and why is that prediction rejected?
- 0.8c; subtracting frame speed conflicts with the postulate.
- 1.2c; adding frame speed conflicts with the postulate.
- c; adding frame speed agrees with the postulate.
A sealed inertial lab measures vacuum light speed c. Can this internal experiment establish that the lab is at absolute rest?
- No; every inertial lab measures the same vacuum light speed c.
- Yes; only an absolutely stationary lab measures vacuum light speed c.
- Yes; uniform motion changes the measured vacuum light speed.
A lamp emits a vacuum light pulse, and a detector later receives that same pulse. Can another inertial frame place reception before emission?
- Yes; spatial separation permits either causal order.
- Yes; fixed light speed reverses the causal order.
- No; light connects the events and preserves their causal order.

Answer key

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Two rules that rebuilt time W1-mt_kZqVQ18bbc-s1

A nonrotating frame moving at constant velocity. · An inertial frame has no acceleration or rotation. Constant speed around a circle still involves changing velocity.
Same laws in inertial frames; vacuum light speed is c. · The postulates concern physical laws in inertial frames and the invariant speed of light in vacuum.
False · The midpoint train pulse lights both doors simultaneously in train coordinates, but rear illumination occurs first in platform coordinates.
The farther flash was emitted before the nearer flash. · At the same speed c, the farther signal has a longer journey. To arrive together, it must have left earlier.
Rear illumination precedes front illumination. · Both pulses travel at c. The rear door moves toward its pulse, while the front moves away from its pulse.
1.2c; adding frame speed conflicts with the postulate. · Ordinary forward addition gives c+0.2c=1.2c. The second postulate instead requires platform speed c.
No; every inertial lab measures the same vacuum light speed c. · The same physical laws and vacuum light speed apply in every inertial lab. This measurement cannot select absolute rest.
No; light connects the events and preserves their causal order. · The same light pulse connects these events. Their causal order is invariant; they are not spacelike-separated.