Force and Motion
2.6 Understanding Impulse and
Impulsive Force
IMPULSE
• Is defined as the product of a force, F acting on an
object of mass, m for time ,t
• Impulse = Force x Time
• Impulse = Ft
• Also can be define as the change of momentum
• Impulse= mv – mu
• Impulse ,Ft = mv – mu
• Unit kgms-1 or Ns
• Is a vector quantity
IMPULSIVE FORCE
• Large force that acts over a short period of time during
collision or explosion
• Also can be define as the rate of the change of momentum in
a collision or an explosion
• Formula :
• F = mv – mu
t
• Unit kgms-2 or N
• Example involving impulsive force:
– Football
– Playing golf
– Playing baseball
– Playing tennis
– Playing badminton
Example 1:
Solution
Example 2
Solution
INCREASING THE TIME IMPACT TO
REDUCE THE IMPULSIVE FORCE
DECREASING THE TIME IMPACT TO
INCREASE THE IMPULSIVE FORCE
Exercise 1
• A boy hits a 0.50kg ball and sends it moving
the opposite direction. Figure shows the
magnitudes of its velocity before and after
being hit respectively. The time of contact
between the land and the ball is 0.05s.
15 ms-1
20 ms-1
Calculate :
1. The impulse applied
to the ball.
2. The impulsive force
exerted on the ball
by the hands.
Exercise 2
• A 300g ball is thrown horizontally towards a
vertical wall at a velocity of 12ms-1. On
impact, the ball bounces back horizontally at a
velocity of 10ms-1. If the ball is in contact with
the wall for 0.02s, find:
a) The impulse
b) The force exerted on the ball.
Exercise 3
• Figure shows a 2kg wooden block initially at
rest on a smooth surface. A force of 8N is
applied on the wooden block.
u=0
8N
2 kg
t = 0s
8N
v
2 kg
t = 3s
• If the force acts for 3s:
a) What is the impulse on the block
b) What is the velocity of the wooden block
after 3s?
Exercise 4
• A tennis ball and a piece of mud with the
same mass ( 0.060 kg) and moving at 9ms-1
both strike a wall. The mud sticks to the wall
while the ball rebounds at 6 ms-1. Find the
impulse on each object.
9ms-1
Mud
9ms-1
Tennis ball
6 ms-1