Name: Grade and Section: Score: School: Teacher: Subject: General Physics 2 LAS Writer: JEREMIAH S. SABRIDO Content Evaluator: EMMA T. SURITA MICHAEL DAVE NALAGON Lesson Topic: The Postulates of S eclal Relativit Quarter 4 Wk. 6 LAS 2 Learning Targetls: State the Postulates oi Special Relativity and their Consequences. STEM-GP12MP-lVg-39 Reference(s): Holzner 3., 2010. Physics ii for Dummies. 111 River St. Hoboken, NJ 07030-5774: Wiley Publishing, Inc., pp.249-253. The Postulates of Special Relativity Special relativity is a theory that predicts how events are measured with respect to various observers who can be in motion with respect to the event. An event is just a physical happening, such as the explosion of a recracker or the ticking of a clock or a train's passing a certain point. Events happen at a particular place and time, as measured by the people who observe them. Those people can be moving with respect to the event, or they can be stationary with respect to the event. For example, in Figure 1, a firecracker goes off, causing a ash of light. That's an event, and two observers watch it. One observer is stationary with respect to the firecracker, and the other observer is moving in a rocket in a straight line at a constant speed with respect to the firecracker. Each observer carries his or her own coordinate system, as the figure shows, and the observers each measure the event its location and time with respect to their individual coordinate systems and clocks. So each observer gets his or her own x, y, and z coordinates for the event and his or her own time. Special relativity is all about relating the measurements that the two observers make. The coordinate systems and clocks that the observers carry with them are called their reference frames, or their frames of reference. So why is it "special" relativity? Each observer's reference frame is a special type of reference frame an inertial reference frame. An inertial reference frame is just one that's not accelerating. When Einstein came up with the theory of special relativity, he started with two postulates, or assumptions, that the theory rests on. The postulates are: The relativity postulate which states that the laws of physics are the same in all inertial reference frames, The speed of light postulate which Firru TE 1 Firecracker states that the speed of light in a vacuum (c) always has the same value in any inertial reference frame, no matter how fast the observer and the light source are moving with respect to each other. The relativity postulate The relativity postulate tells you that one inertial reference frame is as good as another, and you can't tell them apart with experiment. For example, if you're in one inertial reference frame and someone else is in another, you can't tell those frames apart through tests. 50 if you're in the rocket back in Figure 1, it's just as valid to say that the Earth is moving toward you as it is to stand on the Earth and say that rocket is moving toward you. That's what relativity is all about. The speed of light postulate The speed of light (c = 3x1CI'5 mic) is a constant, independent of the relative motion of the source. If you're in one car going 5 meters per second and are approached by another going 10 meters per second, you're moving at 15 meters per second with respect to the other car. So if you're standing by the side of a road and a car approaches you at 10 meters per second with its headlights on, wou ldn't you measure the speed of light from the headlights as c + 10 meters per second? That's not how it works with the speed of light, however, or with speeds approaching the speed of light. As the postulate says, the speed of light from the headlights of the car coming toward you would be c, not c + 10 meters per second. ACTIVITY 1: FACT or BLUF. Write FACT if the statement is correct and BLUFF if it is incorrect. 1. Earth can be an inertial frame of reference. 2. In special relativity, ifa body is moving without an external force, then it'll continue to move in a straight line at constant speed this is the inertial motion. 3. The second postulate of special relativity states that the laws of physics are the same in all inertial reference frames. 4. The speed of light in empty space has the same value for all observers regardless of their velocity. 5. The first postulate argues that a spaceship, for example, cannot measure its speed relative to empty space, but only relative to other objects