We see motion all around us – opening a door, kicking a football or lifting a school bag all involve some push or pull. This chapter explains rest and motion and why they are relative, what a force is, the difference between contact and non-contact forces, the types of motion, how to find speed, uniform and non-uniform motion, and ends with a look at robots.
1. Motion and Rest
- Motion: When there is a change in the position of an object with respect to time, it is called motion.
- Rest: If the object remains stationary, it is called rest.
- A book lying in the middle of a table is at rest; when it is pushed from one place on the table to another, it is moving.
Rest and Motion are Relative
Anitha and Babu stand at a bus stand. Their friends Reka and Mohan get into a bus to Thanjavur and the bus starts.
| Observer | Where the observer is | Mohan appears to be |
|---|---|---|
| Babu | At the bus stand, under a tree | In motion – he moves along with the bus |
| Reka | Sitting beside Mohan in the bus | At rest – he stays at one place |