Moving on With Momentum

B and F Blocks had their introduction to momentum and the impulse-momentum theorem. An object's momentum - the inertia in motion - is affected by the size of the force it experiences and the duration that the force acts on the object. We looked at examples where small forces produced large momentum change (through long time intervals) and where large forces produced small momentum change (through tiny time intervals). Remember that momentum is a vector and inherits the direction piece from velocity. Because of this, it is critical to properly assign and track signs when calculating momentum change.

E Block conducted their impulse-momentum theorem lab, comparing the equivalence of the two for a stiff and loose rubber band. Make careful calculations of momentum change and explain any variations between the measured impulse and the calculated change of momentum. We'll discuss the impulse-momentum theorem tomorrow and use the lab to highlight the discussion.

C Block took a look at conservation of momentum. In a closed system, the total momentum of objects in the system stays the same, regardless of the interactions they experience. However, the momentum of individual objects will change. We looked at how Newton's 3^rd Law of Motion and the idea of impulse mandated conservation of momentum for two objects striking each other (the simplest model) and discussed common scenarios encountered in problem solving. Remember that for systems that start at rest (like a cannonball in a cannon), momentum is still conserved once the cannonball is fired. The cannonball and cannon have equal and opposite changes of momentum, which would still sum to a total momentum of zero. We could use that information, then, to calculate the speed of the cannonball or the recoil velocity of the cannon, if necessary. We'll go over your homework problems tomorrow before taking a closer look at the idea of a "collision."