Special Relativity Cf E Higher Physics Relative motion
- Slides: 12
Special Relativity Cf. E Higher Physics
Relative motion �Motion is relative. �This means that whenever we measure how fast an object is moving, we have to state what the velocity is measured relative to (usually the Earth) What is the speed of the walker on the train………… a) Relative to the train b) Relative to the stationary observer mythbusters
The speed of light �Early experiments showed the speed of light in a vacuum is absolute �It never changes no matter how the light source or an observer is moving. �It doesn’t have to be measured relative to anything!!!! �This led Einstein to develop his: Special Theory of Relativity.
Einstein’s 2 Postulates Einstein’s Special Theory of Relativity has 2 basic ideas (called postulates) at its foundation: �The speed of light is constant to all observers regardless of their velocity (3 x 108 ms-1 in a vacuum) �The laws of physics are the same for all freely moving observers (In other words, there isn’t an experiment that you can do that can tell you that you are moving at a steady speed or not)
Special relativity has some strange consequences for objects that are travelling at speeds approaching the speed of light. . Two of these are: An observer will see moving clocks tick slower than stationary clocks. Moving objects appear shorter than they actually are. There are literally hundreds of videos on You. Tube explaining Special Relativity in “simple terms”……. . Here are just a few…… �Brian Cox �City girl �Science ABC �Bombay Guy �The Physics Girl �frames of reference
Time dilation �Fast moving clocks appear to tick slower than stationary clocks. �This stretching of time is called Time Dilation �Einstein developed an equation that can be used to calculate the difference in the times measured by 2 clocks moving relative to each other. Where: t’ = the stationary observers time t = time on the moving clock v = moving clocks velocity c = speed of light There is a (relatively) straight forward derivation of this equation that uses the idea of a moving “light clock” It requires no more than a knowledge of pythagorus’ theorem. It is not in the course but if you are interested see here…watch (Thanks Mr Smith)
Example 1 �How much slower would a clock be observed to tick on a spaceship traveling at 2. 8 x 108 ms-1 �Let’s just think about 1 second on the moving clock…. . So a stationary observer would see that it takes 2. 78 s on his clock for each tick on the spaceship clock! The space ship clock appears to tick slower. Weird!!
Example 2 �
Length contraction �Another consequence of Special Relativity is that objects travelling at speeds approaching the speed of light are observed to be shorter in length. �This is the length contraction equation: Notice the similarity with the time dilation equation. A stationary observer will observe a moving object to have a shorter length than someone on the moving object!! Weird!!
Example �A spaceship is 200 m in length when it is on the Earth, measured by a stationary measurer. �Calculate the length of the spaceship as measured by a stationary observer on Earth if it whizzes past the Earth at: �a) 2, 500 m s-1 �b) 2, 500, 000 m s-1 �c) 250, 000 m s-1 Answers: 200 m 199. 93 m 110. 55 m
Effects of Special Relativity As you approach the speed of light : • Time is observed to slow down until it would take infinitely long for a single tick! • Length is observed to contract to zero Time for 1 second (s) �The effect of special relativity are noticed unless an object is travelling at more than 10% of the speed of light.
One final effect – (not in the Higher course) �As objects approach the speed of light their mass is observed to increase. �At the speed of light your mass would become infinite and therefore you would need an infinite force to acceleration you even faster. �This is why nothing can ever travel faster than the speed of light. �This relationship led Einstein to mass energy equivalence and E = mc 2
- Mythbusters relative velocity
- General vs special relativity
- Special relativity equations
- Special vs general relativity
- Equations of motion higher physics
- Special relativity
- Michelson morley experiment
- Postulates of special relativity
- Modern physics means
- Momentum special relativity
- Special relativity summary
- Albert einstein theory of special relativity
- "universal equations"