Saturday, 20 July 2013

Gravity and Accelerated Motion

If you are on Earth and jump, you will land back on the surface of Earth. Now imagine you are sealed in a box and accelerated to space where there is 0 gravity. A rocket booster is accelerating your sealed box at 9.81m/s^2. Now if you jump you will again land back on the box as the box is accelerated. In simple words, you won't feel any difference between Gravity (on Earth) and Accelerated Motion (in the sealed box). This made Einstein realize that Gravity is nothing but accelerated motion.

A person can't distinguish between the two situation

Einstein formulated a proposition called Principal of Equivalence which stated that Gravity and Accelerated motion are two different perspective of the same thing. It also stated that there is no experiment which can differentiate between rest position of gravitational field and accelerated motion. He took the example of sealed boxes to explain the cause.

Accelerating frames of reference

Inertial reference frames are reference frames which move at a constant velocity. They must have constant speed and constant direction. Another condition for Inertial frames of reference is that it must not be in any kind of Gravitational field. As gravity is accelerated motion, so for a frame of reference to be inertial, it must not be accelerated.

An accelerating reference frame is a reference frame which is speeding up, slowing down, or changing direction. Since Gravity is described as Accelerated motion, an accelerating frame of reference is one which under the influence of a strong or weak Gravitational field. An inertial object (or a frame of reference) is at rest or in constant motion. As soon as it is influenced by Gravity it becomes accelerated frames of reference.

Time Dilation in Accelerated frame of Reference

In Inertial frame of reference, Time slowed down because Light clocks were slower (Refer Time Dilation). But in accelerated Frame of reference Time either speed up or slow down. This is because when the object is accelerated up, its speed constantly increase, forcing light to cover longer distance and slowing down the time and vice versa. In simple words, acceleration is inversely proportional to Time. The mathematics behind such effects is too complicated and needs very high knowledge of mathematical function.

The following video would help you understand Gravity and Accelerating motion :

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