Question

What is meant by the statement 'rest and motion are relative terms?' Give example to show it.

Answer 1

Rest and motion are relative terms. This means that, you can say that a body is at rest or motion, only if you compare it with another body, or any other physical object.
This comaprison is called relativity.

Consider a person sitting in a moving bus. Just infront of him another passenger is sitting. With respect to the other passenger, this man is at rest, even when bus moves. This is because, the relative distance between the two men are not changing. They are always equidistant.

But, with respect to a tree outside, the man is in motion, because, as the bus moves, the tree is still not moving(rest), but the man moves away.

Now, the tree was at rest in previous case, with respect to his surroundings, that is other trees, soil etc. But when you go to space and stand on the sun( imagine) the tree is in motion with the earth as the earth moves around the sun. Along with the earth, the tree also moves around the sun.

So, if someone says, man is at rest, is that statement true or false? You cant say, because, with respect to his seat, or othe man, he is at rest, but with respect to tree or sun, he is at motion. So the statement, man is at rest, or tree is at motion are all invalid physical statements.

But statements like, man is in motion with respect to tree is a valid statement. As rest and motion is valid only when compared, they are called relative terms.