Introduction to Momentum (P) Yes it is a vector mister!!!!! Introduction to Momentum (P) And you

THE LAWS OF PHYSICS 1) Newton (3 laws) (inertia, F=ma, =/opp F) 2) Kepler (3 laws) (orb. Ellipse, =areas in =t, R3/T2 = 1) 3) The conservation of Energy (only conversion of forms - transformations) 4) The Conservation of Momentum!!!!!!

Momentum = P = ????? P = mv P is conserved for a system with no external forces acting on it (this is an important qualifier) That means that the total momentum in the starting conditions = the total momentum in the final conditions Rolling balls demo here…with conceptual equations

Some fun examples for you 1) A book sliding across a table Is P conserved???? It has mass and velocity! But it has the external force of friction acting on it – so NO P is not conserved!!!!!!!!

What about Newton’s Cradle Really good ones will continue for an hour For that time P is conserved (transferred) Notice how 1 mass  1 mass How 2 masses  2 masses Newton’s cradles demos here...

What about KE??? You can not assume KE is conserved The basic rules to go by are: In an elastic collision (where things bounce off each other) KE IS CONSERVED ∑ KE prior to collision = ∑ KE after collision In an inelastic collision (where things stick together after they collide) KE IS NOT CONSERVED

How about a simple example If a 5 kg dog is moving at 3 m/s, what is the: P ? = KE? = mv = 15 kg m/s ½ mv2 = 22.5 J

Another example please Another example please? 50 kg car,10 m/s, 80 kg truck, unknown V – after collision all stopped Initial momentum = final momentum (m1v1 + m2v2)o = (m1v1 + m2v2)f ((50)(10) + (80)(?) = (50)(0) + (80)(0) Therefore V2 initial = - 6.25 m/s !!! Minus because we are using the coordinate system

Try the same calculation to see if KE is conserved And you will find it does not work out with the same calculated velocities. Remember the velocities would be squared, so the negative V becomes positive… It is a mess – but if you do not want to take my word for it, please try it yourself!

And that is all (for now) for the momentum intro. Prior to working on the lab – Let’s discuss a related topic

IMPULSE ( J ) Play slow motion video here www.youtube.com/watch?v=XjwO9InuFJk https://www.youtube.com/watch?v=zG22qQydPVQ Why is it that the bungee cord does not just pull the jumpers legs off???

Impulse = ??? J = F Δt (units are N s ) How are impulse and momentum related????????

The Impulse – momentum theorem F Δt = ΔP = mvf - mvo Play the Glasgow impulse video here www.youtube.com/watch?v=bKLrj3UFqQI

NOW 4 groups work on the lab The other groups work on the worksheet questions – and work on the lab when it opens up When the air track groups finish their data collection – they can start on the questions