Momentum and Impulse

C and F Blocks started their unit on momentum today. B Block had a discussion focusing on momentum, impulse and the impulse-momentum theorem. Momentum, often viewed as the measure of motion, is the product of mass and velocity. Because of the velocity piece, momentum is a vector with the direction matching the direction of the velocity. This becomes very important when working with momentum change. If directions changes from positive to negative (right to left, north to south), you have to be sure to include the proper signs in your calculations. When an object's momentum does change, we would expect that a force was at the root of it, since the piece of momentum that changed was almost certainly the velocity piece. And, since a change of velocity indicates acceleration, we know a force is promoting the momentum change we measure. But, the duration of the applied force also plays a part and that leads to the concept of impulse.

Impulse is the product of force and time interval. The same impulse can exist for two different forces, if the time interval is also different. A 10 Nxs impulse can be achieved through 5N and 2s, 10N and 1s or 1N and 10s. And all of these will produce the same change in momentum of the object. So, it depends on the situation - do you need a small force or a large force - that will set the time you need to apply the force. We discussed the need for follow-through in sports and the science behind safety devices such as air bags and safety nets and will look more at impulse and momentum in lab, as F Block did today. The lab today used a force sensor to directly measure the impulse acting on a moving cart and a motion detector measured the velocity changes produced by the impulse. Make careful calculations of the change of momentum when working on your lab and think about why it does or does not match the measured impulse and how the loose and tight rubber bands compared in changing the motion of the cart.

B and E Blocks took their work and energy exams and will start on momentum and impulse tomorrow.