# Acceleration

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