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# Momentum and Impulse - PowerPoint PPT Presentation

Momentum and Impulse. Momentum. Momentum . Inertia/mass in motion Symbol- p Equation p = mv Units: kg • m/s VECTOR. inertia. In motion. A large truck has more momentum than a car moving at the same speed because it has a greater mass.

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### Momentum and Impulse

• Inertia/mass in motion

• Symbol- p

• Equation p = mv

• Units: kg • m/s

• VECTOR

inertia

In motion

• A Thought Experiment: same speed because it has a greater mass.

• Suppose that you were captured by an

evil physicist who gave you the following choice:

• You must either:

• Stand in front of a 1000 kg. truck moving at 1 m/s, or

• Stand in front of a 1 kg. frozen meatball moving at 1000 m/s.

• …think…

Plug and Chug same speed because it has a greater mass.

p = mv = (2500 kg)(18 m/s) = 45000 kg m/s

Plug and Chug same speed because it has a greater mass.

4.68 kg m/s

p = mv v = p/m (4.68)/(7.3) = 0.64 m/s

Impulse equation same speed because it has a greater mass.

• Ft = Δ mv

• Impulse is a force applied over a certain time period

• An impulse is required to change the momentum of an object. A change in momentum creates an impulse

Change in momentum

impulse

Impulse and Momentum same speed because it has a greater mass.

• Impulse = Change in Momentum

• = Final (mv) - Initial (mv)

• F t = mDv

Example:  Wall exertsa force of 10,000 N.The contact time is0.01 s.------------------------------Impulse = F t              = 100 N-s

Which would do more damage- stopping a truck, moving at 60 mi/h, by running into:

• A brick wall? a hay stack?

Why is follow through so important? mi/h, by running into:

• A golfer follows through on a swing to increase the ball’s velocity and make it travel farther.

• Following through keeps the club head on the ball for a longer period of time. Since time and velocity are directly proportional, increasing the time of contact increases velocity

Why does a batter stop the bat during a bunt? mi/h, by running into:

• Answer using words and the impulse equation

Decreasing time to increase force mi/h, by running into:

By swift execution she makes the time of contact very brief and correspondingly makes the force of impact huge!

If her hand is made to bounce upon impact, the force is even greater!

Which is more likely to break a window? mi/h, by running into:

• A rubber ball

• A clay ball

• Neither

Δ v of rubber ball is greater so impulse must be greater

Bouncing mi/h, by running into:

• Impulses are greater when bouncing takes place

• Tis because the impulse required to bring something to a stop and then, in effect, “throw it back again” is greater than the impulse required merely to bring something to a stop

Law of Conservation of Momentum mi/h, by running into:

• The momentum lost by one object is gained by another object….the total amount is constant or conserved (cannot be created nor destroyed)

• Momentum before = momentum after OR…

• Momentumintial = momentumfinal

• OR Pi=Pf

• system – a collection of objects

• Closed system – no objects enter or leave

• Isolated system – no net external force acts on it

Examples mi/h, by running into:

• Conservation of Momentum: If there are no external forces, the total momentum for a system remains unchanged.

• Example 1: a person sitting inside a car pushing against the dashboard

• Example 2: a bullet fired from a rifle

Momentum of system is zero mi/h, by running into:

Momentum Before = 0-------------MomentumAfter = 0-------------After firing, the oppositemomentacancel.

Elastic collision mi/h, by running into:

• Objects bounce off each other without deforming or losing energy

• Kinetic Energy is conserved

Elastic Collisions mi/h, by running into:

m1v1i + m2 v2i = m1 v1f +m2v2f

**note that there are TWO final velocities**

Inelastic Collision mi/h, by running into:

• Objects stick together or are deformed with the loss of energy

Inelastic Collisions mi/h, by running into:

m1v1i + m2 v2i = (m1+m2)vf

Momentum Warm up mi/h, by running into:

• What is the momentum of an object that is 30kg and is moving at 5 m/s?

2. A 200kg motorcycle slows from 10m/s to 5 m/s.

a. What is the change in momentum?

b. How much impulse is required to change the momentum?

c. If the impulse was applied for 2 seconds, how much force was applied?

3. A huge rugby player rams into a smaller player and knocks him 5m away. What type of collision is this?