Cars

IMPULSE AND IMPULSIVE

FORCE

Impulse is defined as change in momentum of an

object.

IMPULSE

F = Impulsive force, t = time, m = mass, v & u = velocity

Ft = mv-muChange of momentum

The product of impulsive force (F) and the time of impact (t).

Impulse

Equations: Ft = mv-mu ……….?

F = m at

uva

----------

F = Impulsive force, a = acceleration, t = time, m = mass, v & u = velocity

)(t

uvmF

Ft = mv-mu

Impulsive force is defined as the rate of change of momentum of an object in a collision or explosion.

IMPULSIVE FORCE:

Impulsive Force is a large force that acts over a short period of time during collisions or explosions.

F = Impulsive force, t = time, m = mass, v & u = velocity

tmumvF Change of

momentumTime of impact

The shorter the time of impact, the bigger the impulsive force.

Example of Impulsive Force:

a.falling down the glass to the floor

b.Hitting a nail using hammer

c.Kicking a football

d.Collision of cars

e.Striking a tennis ball

f.Etc.

How to Decrease the Impulsive Force…………?

How to Increase the Impulsive Force…………?

Increase the time of impact

Decrease the time of impact

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.

3. Safety Car

2. When jumping from a high building.

4. Parachute

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.

Solve Problems

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:

NFs

smxkgsmxkgF 500000,

05.0

)251000()01000( 11

t

mumvF

Group Activity

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.

a. Calculate the impulse when his legs hit the ground.

b. What is the impulsive force on the resident’s legs if he bends upon landing and takes 0.5 s to stop?

c. What is the impulsive force on the resident’s leg if he does not bend and stops in 0.1 s?

d. What is the advantage of bending his legs upon landing?

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DISCUSSION

Summary