Thursday, Oct 28, 2010

Handed back Ball and Ramp Labs
Handed back Act-A-Graph Lab
Handed back Act-A-Graph homework sheets

Reviewed Ball and Ramp Lab
When an object rolls, it picks up speed. It "alters" its motion - it accelerates.
Reviewed the graph

We saw the same graph when we did the Picket Fence demo
Distance vs Time graph showed the object gained speed as it fell.
The velocity vs time graph was a straight line showing that it picked up speed at a constant rate. We measured that rate to be 9.6-9.7 m/s/s. The accepted value is about 9.8 m/s/s. We will round that off to 10 m/s/s

Went over how to calculate:
How fast?
How far?
for an object dropped from rest.

Did several examples going around room.
Put recipe on board.

As an object falls, it picks up speed. The longer it falls, the greater the speed. To get something changing its speed, you apply a force. The longer you apply the force, the greater the change in speed.

To get the greatest change in speed, you apply the largest force for the longest time.

Impulse = Net force * time
You change the motion by applying an impulse.
When you pulled out the tablecloth, the force was too small and acted for too short a time to move the table setting. The impulse was too small.
Gave example of calculating impulse: Fnet = 10 N, t = 2 sec, impulse = 20 Ns

A bowling ball and tennis ball will fall at the same rate if air resistance is negligible...so, are they just as easy to stop. NO!! The bowling ball has something more.

Tossed bowling ball to student who caught it and said, "ooomph". The bowling ball has more ooomph because it has more mass. But...you would rather stop a massive bowling ball than stop a light bullet. The bullet also has a lot of ooomph because it has a lot of speed.

Another name for ooomph is momentum.
ooomph = momentum = mass * velocity = p
The symbol for momentum is p (get from ooomph)
Gave an example of calculating momentum: mass = 3 kg, v = 4 m/s, p=12 kg m/s

The equation that relates the two is:

Impulse = change in momentum
Fnet * t = m*vf - m*vi

For the same change in momentum, you can have a large force acting for a short time or a small force acting for a long time.

Applied this idea to jumping out of a burning building into a net, landing while flexing your knees, catching a baseball, crumple zone of car.

Did egg toss lab even though it was sprinkling outside.

Came in and did marshmallow demo. Longer barrel allows force to act for longer time giving more impulse and more speed.