**Question 4**

**‘All rest and motion are relative’- Explain. Define displacement, speed, velocity, acceleration and retardation. **

**Answer**

“All rest and motion are relative” means that the state of motion of an object depends on the observer’s frame of reference. In other words, an object may be considered to be at rest or in motion depending on the reference point of the observer. For example, a person sitting in a moving train may appear to be at rest to the other passengers but may be moving relative to an observer standing outside the train.

- Displacement is the change in position of an object from its initial position to its final position, measured in a specific direction. It is a vector quantity and is denoted by the symbol s.
- Speed is the rate of change of distance with respect to time. It is a scalar quantity and is denoted by the symbol v.
- Velocity is the rate of change of displacement with respect to time. It is a vector quantity and is denoted by the symbol v.
- Acceleration is the rate of change of velocity with respect to time. It is a vector quantity and is denoted by the symbol a.
- Retardation is the negative acceleration that opposes the motion of an object. It is also known as deceleration and is denoted by the symbol -a.