Week 11 Presentation 1 Impulse and Momentum

Impulse and Momentum Definitions:  Momentum is the product of the mass and velocity of an object. Momentum is resistance to stopping, so it ’ s kind of inertia for moving bodies.  Impulse is the product of the average force multiplied by the time interval over which it acts: the change in momentum. Hitting a baseball with a bat applies a force that changes the ball ’ s direction, changing its velocity and momentum.

Impulse and Momentum Units:  Impulse = Ns (Newton-second) “ J ”  Momentum = kgm/s “ p ” Watch a video on the link below:

Impulse and Momentum Equations:  Momentum p = mv  Impulse J = Ft  p = momentum, m = mass, v = velocity F = total net force applied, J = impulse

Impulse and Momentum Impulse-Momentum Theorem:  FΔt = p 2 – p 1 The impulse on an object (FΔt) is equal to the change in momentum (p 2 – p 1 ) that is causes. You can also find impulse using a force-time graph like the one above. The impulse would be the area under the curve.

Impulse and Momentum Momentum example problem:  What is the momentum of an object with mass of 2.00kg and a velocity of 40.0m/s? p = (2.00kg)(40.0m/s) = 80.0 kgm/s Impulse example problem:  A force of 30000N is exerted for 4.00s on a 95,000kg mass. What is the impulse of the force? J = (30000N)(4s) = Ns

Impulse and Momentum I-M theorem example problem:  A 2200kg SUV traveling at 26m/s can be stopped in 21s by gently applying the brakes, in 5.5s in a panic stop, or in 0.22s if it hits a concrete wall. What average force is exerted on the SUV in each of these steps? (you ’ ll want to rearrange the theorem for this.) Gently braking F = -2.7x10 3 N Panic braking F = -1.0x10 4 N Hitting the wall F = -2.6 x 10 5 N

Impulse The impulse of a force is equal to the change in momentum of the body to which the force is applied. This usually means a change in velocity. F·t = m·  v=  P where  v = v f - v i The same change in momentum can be accomplished by a small force acting for a long time or by a large force acting for a short time.

Impulse The area under the curve in a force vs. time graph represents the change in momentum (m ·  v). If your car runs into a brick wall and you come to rest along with the car, there is a significant change in momentum. If you are wearing a seat belt or if the car has an air bag, your change in momentum occurs over a relatively long time interval. If you stop because you hit the dashboard, your change in momentum occurs over a very short time interval.

Impulse If a seat belt or air bag brings you to a stop over a time interval that is five times as long as required to stop when you strike the dashboard, then the forces involved are reduced to one-fifth of the dashboard values. That is the purpose of seat belts, air bags, and padded dashboards. By extending the time during which you come to rest, these safety devices help reduce the forces exerted on you.

If you want to increase the momentum of an object as much as possible, you apply the greatest force you can for as long a time as possible.

Impulse and Bouncing Impulses are greater when bouncing takes place. The impulse required to bring an object to a stop and then throw it back again is greater than the impulse required to bring an object to a stop.