**Q.1: Define rest?**

**Ans: REST:**

A body is said to be in the state of rest if it does not change its position with respect to its surroundings.

**Q.2: Define motion? Write down its types?**

**Ans: MOTION:**

A body is said to be in the state of motion if it changes its position with respect to its surroundings.

**Types OF MOTION:**

There are many types of motion but the common types are given below:

**Translatory Or Linear Motion:**

When a body moves on a straight path and the direction of the motion remains constant during its motion; its motion is called translatory or linear motion.

**Examples:**

- Motion of a boat
- Motion of acar

**Rotatory Motion:**

When a body spins or rotates about a fixed point or axis, its motion is called rotatory motion.

**Examples:**

- Motion of the earth about its axis
- Motion of the blades of an electric fan

**Vibratory Or Oscillatory Motion:**

When a body moves to and fro about its mean position, its motion is called vibratory or oscillatory motion.

**Examples**:

- Motion of a swing
- Motion of pendulum of a clock

**Q.3: Define kinematics, mechanics and dynamics?**

**Ans: KINEMATICS:**

The word kinematics is derived from Greek word ‘kinema’ meaning motion. The branch of physics which deals with the motion of objects without any reference to the force or agent causing the motion is called kinematics.

**MECHANICS:**

Mechanics is the branch of physics that deals with the kinematics and dynamics of objects.

**DYNAMICS:**

The word dynamics is taken from a Greek word ‘dynamic’ meaning power. So dynamics is the branch of physics which deals with the causes of motion and how they affect the motion.

**Q.4: Define scalar and vector quantities with examples?**

**Ans: SCALAR QUANTITIES:**

Physical quantities, which are completely specified by their magnitude only, are called scalars quantities. The scalar quantities can be added, subtracted and multiplied by simple arithmetic methods.

**Example:**

Mass, time, distance, speed, work, energy, temperature, charge etc.

**VECTOR QUANTITIES:**

Physical quantities, which are completely specified by their magnitude and direction both, are known as vector quantities.

**Example:**

Displacement, velocity, acceleration, force, weight, torque, momentum etc.

**Q.7: Write down the types of speed?**

**Ans: Types OF SPEED:**

There are following types of speed:

**Uniform Speed:**

If a moving body cover equal distance in equal interval of time, the speed of the body is called uniform speed.

**Variable Speed:**

If a moving body does not cover equal distance in equal interval of time, its speed is called variable speed.

**Average Speed:**

If we divide distance covered by a moving body by time interval then we get average speed.

**Q.8: Define velocity? Write down its formula and unit?**

**Ans: VELOCITY:**

The distance covered by the body in a particular direction is called velocity.

**Q.9: Write down the types of velocity?**

**Ans: Types OF VELOCITY:**

There are the following types of velocity:

**Uniform Velocity:**

When speed and direction of motion of a body do not change, the velocity is said to be uniform.

**Variable Velocity:**

The velocity of the body changes of either its speed changes or direction or both of them, such a velocity is called variable velocity.

**Average Velocity:**

If we divide total displacement covered by the moving body by total time taken by the moving body then we get average velocity.

**Q.10: What is acceleration? Write down its formula and unit?**

**Ans: ACCELERATION:**

The rate of change of velocity is called acceleration. It is denoted by “a”. It is a vector quantity.

**Q.11: Write down the types of acceleration?**

**Ans: Types OF ACCELERATION:**

There are the following types of acceleration:

**Positive Acceleration:**

If the velocity of a body increases continuously then the acceleration is said to e positive or simple acceleration and its direction as that of the motion.

**Negative Acceleration:**

If the velocity of a body decreases continuously then the acceleration is said to be negative and is called deceleration or retardation. Its direction is opposite to the direction of motion.

**Uniform Acceleration:**

If the velocity of a body changes by equal amount in equal interval of time then its acceleration is said to be uniform acceleration.

**Variable Acceleration:**

If the rate of change of velocity is variable then the acceleration is said to be variable acceleration.

**Zero Acceleration:**

If a body moves with uniform velocity then it has zero acceleration.

**Average Acceleration:**

The ratio between total change in velocity and time is called average acceleration.