4. Cars

5. IMPULSE AND IMPULSIVE FORCE

6. Impulse is defined as change in momentum of an object.
Ft = mv-mu
Change of momentum
F = Impulsive force, t = time, m = mass, v & u = velocity

7. Ft = mv-mu Ft = mv-mu Impulse Equations: ……….? F = m a
The product of impulsive force (F) and the time of impact (t).
Equations:
Ft = mv-mu
……….?
F = m a 
Ft = mv-mu
F = Impulsive force, a = acceleration, t = time, m = mass, v & u = velocity

8. The shorter the time of impact, the bigger the impulsive force.
Impulsive Force is a large force that acts over a short period of time during collisions or explosions.
Impulsive force is defined as the rate of change of momentum of an object in a collision or explosion.
Change of momentum
Time of impact
The shorter the time of impact, the bigger the impulsive force.
F = Impulsive force, t = time, m = mass, v & u = velocity

9. Example of Impulsive Force:
falling down the glass to the floor
Hitting a nail using hammer
Kicking a football
Collision of cars
Striking a tennis ball
Etc.

10. Increase the time of impact
How to Decrease the Impulsive Force…………?
Decrease the time of impact
How to Increase the Impulsive Force…………?

11. An impulsive force needs to be reduced
1. In high jump, when the jumper falls on the mattress, the soft nature of the mattress lengthen the time of collision.
2. When jumping from a high building.
3. Safety Car
4. Parachute

12. The Benefit of Impulsive Force
1. When a hammer is used to hit a nail into wood.
2. An exponent of karate has the capability to split athick wooden slab by bringig his hand down hard onto the surface of wood.
3. In construction, a heavy pile hammer is dropped from a high level onto the top of a pile.
4. When foodstuff such as nuts or onions are pounded using a mortar and pestle (which are both made from stone), the action produces large impulsive forces which crush the food.
5. Kicking a football, etc.

13. Solve Problems

14. Solving Problems
1. A car with a mass of 1000 kg is moving with a velocity of 25 m s-1. It then collides with a tree and is stopped in 0.05 seconds. Calculate the impulsive force acted on the car.
Solution:
Mass of the car = 1000 kg
Initial velocity of the car (u) = 25 m s-1
Final velocity of the car (v) = 0 m s-1
Time taken to stop (t) = 0.05 s
Therefore, the impulsive force:

15. Group Activity

16. Calculate the impulse when his legs hit the ground.
2. A 60 kg resident jumps from the first floor of a burning house. His velocity just before landing on the ground is 5 m s-1.
Calculate the impulse when his legs hit the ground.
What is the impulsive force on the resident’s legs if he bends upon landing and takes 0.5 s to stop?
What is the impulsive force on the resident’s leg if he does not bend and stops in 0.1 s?
What is the advantage of bending his legs upon landing?
Next

17. DISCUSSION

18. Summary