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Posted Wed Oct 12 16:58:00 PDT 2011 by Virgil Peter Denegri (Virgil Peter Denegri).

Science Enterprise, Tampa, USA

Materials Required: Introduction to Physics

Activity Time: 1 hour

Concepts Taught: Speed, Time, Length.

Space and time new concept (spacetime) that derives from Relativity is based on the following: 1. The laws of physics are the same in all inertial frames or reference, and 2. The speed of light in a vacuum is constant.

Special Relativity deals with the above two postulates.

There are two consequences of Special Relativity: Time Dilation and Length Contraction.

As for the concept of time dilation, the moving observer's reference frame experiences the same laws of physics as it is for the observer at rest, but events do not happen simultaneously for everyone. Events that seem simultaneous to the observer at rest are not simultaneous to the moving observer.

Consequently, each tick on the moving observer's clock takes a longer time interval per tick. This is called time dilation. The moving observer's clock slows down. The closer it gets to the speed of light, the slower each tick of the clock gets.

The reason for time dilation is simple. If some object is dropped inside the moving observer's vehicle, from the point of view of the observer at rest, that falling object covers a longer distance as it falls. This means that it would seem to fall faster than if it fell in the observer-at-rest's frame of reference.

However, if the laws of physics are to be the same in all frames of reference, then some measurement in the moving observer's reference frame would be different to experience the same falling speed in both, moving and at rest. Time had to have slowed down in the moving vehicle so that the falling object is measured to fall at the same rate as if falling near the observer at rest.

The equation for time dilation is:

t' = t / square root of (1 -- (v^2/c^2)

where t' = the stretched out time as observed by the stationary observer.

and t = time at the stationary observer.

v = speed of moving observer. In the equation "v" is raised to the second power.

c = speed of light. In the equation "c" is raised to the second power.

As for the concept of length contraction, the reference frame at rest observes measurements of length or distance at the moving frame to be shorter than what the moving observer measures. This is called length contraction.

Therefore, the closer to the speed of light, the shorter the distance that is travelled.

The equation for length contraction is:

L' = L x square root of (1 -- (v^2/c^2)

Where L' is the shorter length perceived by the moving observer.

and L = the proper length measured in the moving reference frame when at rest.

v = speed of moving observer. In the equation "v" is raised to the second power.

c = speed of light. In the equation "c" is raised to the second power.