Aim: How do we explain the impulse momentum-theorem?

Momentum Momentum is mass in motion. Momentum can be thought of as how difficult it is to stop an object. Momentum = mass • velocity p = mv p = momentum m=mass of object v=velocity of object

Momentum The direction of the momentum vector is the same as the direction of the velocity vector. The units of momentum are kg m/s

Problem 1 1. Determine the momentum of a ... 60-kg halfback moving eastward at 9 m/s. p=mv=(60kg)(9 m/s)=540 kg m/s b. 1000-kg car moving northward at 20 m/s. p=mv=(1000kg)(20 m/s)=20,000kg m/s c. 40-kg freshman moving southward at 2 m/s. p=mv=(40 kg)(-2m/s)=-80 kg m/s

Problem 2 2. A car possesses 20 000 units of momentum. What would be the car's new momentum if ... a. its velocity was doubled. (40,000 kg m/s) b. its velocity was tripled. (60,000 kg m/s) c. its mass was doubled (by adding more passengers and a greater load) (40,000 kg m/s) d. both its velocity was doubled and its mass was doubled. (80,000 kg m/s)

Checkpoint Review Units of Momentum? Vector or Scalar? Equation for momentum?

Impulse-Momentum Theorem When an object experiences a force, the object experiences a change in momentum. The change in momentum of an object is called the impulse. The change in momentum of an object is equal to the force acting on it multiplied by the time over which this force acts on the object.

Impulse Momentum Theorem-(Mathematical Form) J = impulse Δp = change in momentum J = Δp = mΔv Impulse Momentum Theorem J = FΔt F= force Δt = change in time Derive the Impulse Momentum Theorem using Newton’s 2nd Law

Calculating impulse In both diagrams below, a toy car of mass 5 kg collides with the wall. Calculate the change in momentum (or the impulse delivered to the car in each case). Δp=pf –pi =mvf –mvi =5kg(-4m/s)-(5kg)(5m/s)=-45 kg m/s Δp=pf-pi=mvf-mvi=5kg(0 m/s)-5kg(5 m/s)=-25 kg m/s

Applying the Impulse-Momentum Theorem A hockey player applies an average force of 80.0 N to a 0.25 kg hockey puck for a time of 0.10 seconds. Determine the impulse experienced by the hockey puck. J=Ft=80N(0.1s)=8Ns 2) Jennifer, who has a mass of 50.0 kg, is riding at 35.0 m/s in her red sports car when she must suddenly slam on the brakes to avoid hitting a deer crossing the road. She strikes the air bag, that brings her body to a stop in 0.500 s. What average force does the seat belt exert on her? Δp=mΔv=J=Ft 50kg(-35 m/s)=F(0.5s) F=-3500 N

Egg Toss Why does the egg break when it hits the blackboard? It changes momentum over a short period of time so the force is great. Why does the egg not break when it hits the sheet? It changes momentum over a longer period of time so the force is smaller.