Question 1 What is meant by the term acceleration?

Question 2 State the S.I. unit of acceleration?

Question 3 Define the term uniform acceleration.Give one example?

Question 4 Define the term non-uniform acceleration.Give one example?

Question 5 What is the acceleration of a body moving with uniform velocity?

Question 6 What type of motion is exhibited by freely falling body?

Question 7 What is retardation?

**Acceleration**

It is defined as rate of change of velocity with time.

Change in velocity

Acceleration = ——————————–

Time taken for change

= Final velocity – Initial velocity

—————————————

Time taken for change

v-u

a = ——

t

S.I. unit is m/s or cm/s.

Acceleration is a vector quantity.

If a body moves with uniform velocity its acceleration will be zero because its velocity is zero.

**Uniform acceleration**

A body has a uniform acceleration if it travels in a straight line and its velocity increases by equal amount in equal intervals of time.

For Ex:Motion of freely falling body, bicycle going down the slope, ball rolling down in inclined plane.

**Non-uniform acceleration**

A body has a non-uniform acceleration if its velocity increases by unequal amount in equal intervals of time.

For Ex:Car running on a crowded city road(At one moment its velocity increases and at other velocity decreases.)

**Retardation/Deceleration/Negative acceleration**

Acceleration can be

1)Negative(velocity decreases):Acceleration

2)Positive(velocity increases):Deceleration

A body is said to be retarded if its velocity decreases.

For Ex: A train is retarded when it slow down on reaching station because its velocity decreases.

Retardation is indicated by negative sign.It means velocity of body is decreasing.

v+u

Average velocity = ——-

2