Physics 2 – Jan 4, 2018 P3 Challenge– A 350 g ball is dropped from 1.35 m. What is its velocity when it hits the floor? Today’s Objective: Momentum and impulse Assignment: Momentum and Impulse Worksheet Agenda Momentum Impulse Alternate 2nd law

Momentum p = mv Note: momentum is a vector !!! Momentum is a very intuitive way to describe how much motion something has. It is proportional to both mass and velocity. Symbol: p Unit: kg m/s (outside IB) or N∙s (IB) p = mv Note: momentum is a vector !!! An object with twice the mass of another object moving at the same speed has twice the momentum. One object moving at twice the speed of an identical object has twice the momentum.

Impulse Impulse is defined as a change in momentum: Symbol: J = p = pf - pi Same unit as momentum. To find a difference in momentums, you need to do a vector subtraction. (Always final minus initial.) Ex: What impulse is experienced by a 225 kg horse that goes from trotting at 2.1 m/s to galloping at 3.5 m/s? Ex: A 450 kg space satellite is traveling at 15 m/s and is hit by a piece of space junk knocking it out of orbit and sending it 45 off it’s initial path. What is the impulse delivered to the satellite relative to its initial path?

Newton’s Second Law (Alternate form) Newton’s original formulation of his second law was not conceptualized as F= ma but rather as a rate of change of momentum. Fnet = p /t How is this equivalent to Fnet = ma?? Rearrange to p = Ft or J = Ft The force here is the force due to a collision that creates a change in momentum over a time for the impact. Consider the relative magnitudes of F and t If a variable force is plotted vs time, the impulse is the area under the curve

Exit Slip - Assignment Exit Slip- For a 350 g ball bouncing on the ground, if it hits the floor with 3.64 m/s and rebounds with the same speed, A) What impulse does it experience? B) If the bounce takes 15.0 ms, what force does the ball impart to the floor? What’s Due on Jan 24? (Pending assignments to complete.) Momentum and Impulse worksheet What’s Next? (How to prepare for the next day) Read 2.4 p98-108 about Momentum