 Pen/Pencil, notebook, calculator at your desk.  EVERYTHING else in the cubbies.  No class Monday (MLK day)  Chapter 6 Test Thursday 1/21 Gen Phys

Momentum Section 3: Impulse Momentum Theorem

 Objects tend to maintain their motion = INERTIA  A net force is required to change motion- Newton’s 1 st Law  F = ma – Newton’s 2 nd Law  If a force is applied, an equal and opposite force will result.  Forces, and other vector quantities, can be added graphically and analytically

 A quantity that relates the mass of an object and it’s velocity.  Ummmmm…..Wasn’t that inertia?  Yes, Newton strikes again!  Momentum is inertia in motion. ◦ Momentum = mass x velocity p = mv CARD !

 In order for momentum to change either mass, velocity or both must change.  Most of the time mass remains constant and velocity changes.  What causes a  v?  FORCE!!!  This force is applied over a time so…….  the product of F and t =  Impulse = Ft J = F  t CARD!

 A soccer player exerts 40 N of force during a 2 s collision with the ball. What impulse does he experience?  List Givens ◦ F = 40 N ◦ T = 2 s  Choose Equation ◦ J = F  t  Plug and Chug ◦ J = (40 N)(2 s) = 80 Ns

 Objects tend to maintain their motion = INERTIA  A net force is required to change motion- Newton’s 1 st Law  F = ma – Newton’s 2 nd Law Stop right there! Let’s take another look at that equation

So F = m x  v  t OR… F  t = m  v This is IMPULSE! This is change in MOMENTUM! What does that mean?

F  t = m  v  This says that Impulse is equal to the change in momentum  It is relevant to our everyday lives to understand the relationship and how it makes us feel. CARD!

 In most cases, by the time you realize that you need to change momentum (come to a stop) your initial velocity is set. ◦ v i = set number ◦ v f = 0 m/s ◦ m doesn’t change  This means that the m  v, change in momentum, side of the equation is set  The Impulse side can be adjusted

  p can be either:  a BIG force x a small time  OR  a small force x a BIG time  Which feels better?

CARD !

 A 125 kg cyclist hits a pothole while traveling at 20 m/s and comes to a, very wet, stop in.2 s. What force does the rider experience?

 List Givens: ◦ m = 125 kg ◦ v i = 20 m/s ◦ v f = 0 m/s ◦ t =.2 s  Choose an equation: ◦ F  t = m  v  Plug and Chug: ◦ F = m  v   t  F = (125 kg)(20 m/s).2s = 12,500 N