THINGS YOU WANTED TO KNOW, BUT WERE AFRAID TO ASK. IMPULSE AND MOMENTUM

I. IMPULSE A baseball hits a bat. The velocity of the bat changed. (Vf-Vi) The velocity of the ball changed. (Vf-Vi) Vi Vf Vi Vf

B. NEWTON’S 3 rd Law For every action (ball hitting bat), there is an equal and opposite reaction (bat hitting ball). FORCE IS THE SAME ON BOTH OBJECTS! BUT : the velocities of the two objects are completely different. WHY?

C. NEWTON’S 2 nd LAW He took his formula F=ma:  Changed it to F = m *(∆v/∆t)  Put ∆t on the other side to get the formula:  Affectionately called fatmav.  NEWTON CALLED F∆t, Impulse  So I = F∆t F∆t=m∆v

II. Momentum A Car and a bus are both going 30 m/s. Which one has more Force?  Neither, the force on both is zero Which on does more damage?  The bus, but why? V V

B. Momentum The bus has more of something, and it is called momentum. Newton named it and wrote the formula: p = mv

III. IMPULSE MOMENTUM THEOREM I = F∆t p= mv F∆t = m∆v Therefore: Impulse momentum theorem is that the impulse on an object is equal to the change in momentum of that object. I = ∆p

IV. Law of conservation of Momentum We are talking about collisions here!  The total momentum of all the objects before a collision must equal the total momentum of the objects after the collision.  Assuming no energy lost (elastic collision)  Reality (inelastic collision) P before = P after

EXAMPLE A rifle with a mass of 5 kg fires a bullet with mass of 3 g at a velocity of 700 m/s. What is the recoil velocity of the rifle? m 1 v 1 = m 2 v 2