Einstein's theory of special relativity describes the motion of objects at near-light speed. It says that the speed of the light is constant whatever the relative speed of the observer, and the laws of physics are the same in all frames of reference. It is called the theory of special relativity because it has to do with relative motion.
Time dilation:
The passage of time appears to be different depending on the relative speed of the observer.
A light beam is bouncing up and down between a mirror at the bottom of a moving train car and a mirror at the top. An observer in the train car would observe the light beam moving straight up and down. A stationary observer outide the train would observe the beam of light travelling zig zag because of the motion of the train. Because the beam travels in a zig zag to the outside observer instead of straight up and down as it does to the moving observer, it appears to be travelling a greater distance then it does to the moving observer. According to Einstein's theory of special relativity, the speed of light is constant. The beam of light would not be able to move faster to compensate for the extra distance. Because of this, the rate at which the beam of light bounces between the two mirrors appears to be slower to the outside observer than it does to the moving observer.
length contraction:
To a stationary observer, an object's length appears to contract as it's speed increases. An object that normally appears 20 meters in length will appear shorter when the object is moving half the speed of light. The height of the object does not appear to change. ----
Special Relativity:
Define:
Einstein's theory of special relativity describes the motion of objects at near-light speed. It says that the speed of the light is constant whatever the relative speed of the observer, and the laws of physics are the same in all frames of reference. It is called the theory of special relativity because it has to do with relative motion.Time dilation:
The passage of time appears to be different depending on the relative speed of the observer.A light beam is bouncing up and down between a mirror at the bottom of a moving train car and a mirror at the top. An observer in the train car would observe the light beam moving straight up and down. A stationary observer outide the train would observe the beam of light travelling zig zag because of the motion of the train. Because the beam travels in a zig zag to the outside observer instead of straight up and down as it does to the moving observer, it appears to be travelling a greater distance then it does to the moving observer. According to Einstein's theory of special relativity, the speed of light is constant. The beam of light would not be able to move faster to compensate for the extra distance. Because of this, the rate at which the beam of light bounces between the two mirrors appears to be slower to the outside observer than it does to the moving observer.
length contraction:
To a stationary observer, an object's length appears to contract as it's speed increases. An object that normally appears 20 meters in length will appear shorter when the object is moving half the speed of light. The height of the object does not appear to change.Source:
http://www.nasa.gov/worldbook/relativity_worldbook.htmlhttp://www.phys.unsw.edu.au/einsteinlight/jw/module4_time_dilation.htm#time
http://www.physicsclassroom.com/mmedia/specrel/lc.cfm