Day+6


 * Day 6, Momentum and impulse.**


 * <>day7>>﻿ ||

Momentum is a property of moving bodies. Students can eaily get confused as to what is the difference between momentum and kinetic energy. The key thing to remember is that momentum is a vector quantity - it has both size and direction, whereas kinetic energy is scalar. The laws and equations that describe changes in momentum, as with much in physics, assume that everything happens on a frictionless plane in a vacuum. These are comparitively rare in nature and so when doing experiments, some allowances need to be made. The session looked at elastic and inelastic collisions and explosions. In these events, momentum is conserved. We used simple digital cameras and the physics tracker software to record changes in momentum of the bodies involved in the events. We also looked at the concept of impulse. Impulse gives the change in momentum of a body. The algebraic derivation is here:

Here are two video clips of my good friend John hitting balls at small children in a park. The film is taken at 1200 frames per second. You should be able to use physics tracker to approximate the force exerted on the ball in each case. Because the Quicktime plugin was causing problems on some browsers, I've put the videos into zip files. They're .mov files. They'll probably run faster if you right click and save to your desktop.

There's some nice information on momentum and collisions on the Physics Classroom site.

Instructions for using tracker to measure momentum in an inelastic collision.



You could also try using tracker to analyse some more interesting video clips: here's a selection of [|road runner clips and suggested uses in the physics classroom]. The thought of catapulting anvils, dynamite traps and rocket skates should appeal to any true physics teacher. There are some useful clips and accompanying materials on momentum on the Physclips site. Also good is this Mythbusters episode (parts one and two)



More questions on momentum and solutions: