Force and Motion

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Force and Motion

• 2.6 Understanding Impulse and Impulsive Force

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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

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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

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Example 1
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Solution
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Example 2
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Solution
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INCREASING THE TIME IMPACT TO REDUCE THE
IMPULSIVE FORCE
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DECREASING THE TIME IMPACT TO INCREASE THE
IMPULSIVE FORCE
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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

• Calculate
• The impulse applied to the ball.
• The impulsive force exerted on the ball by the
  hands.

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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
• The impulse
• The force exerted on the ball.

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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.
• If the force acts for 3s
• What is the impulse on the block
• What is the velocity of the wooden block after 3s?

t 0s t 3s
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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 Tennis ball
9ms-1
6 ms-1