What is REST ? What is Motion ?#!#Are we always moving?

What is meant by uniform motion ?

What Is Rest?|Frame Of Referance|What Is Motion?|Types Of Motion|Types Of Motion (Summary)|OMR|Summary

A shelf moves vertically with simple harmonic motion whose time period of motion is T seconds. Find the maximum amplitude that it can have so that objects resting on the shelf may always remain in contact with it.

When a rigid body is in motion, few particles of the body remain at rest at all times. What kind of motion is the rigid body having?

Does friction always oppose the motion?