Morgan County 7th and 8th grade

A few videos showing a little of the fun we had investigating mass and motion.

First a rocket made of a student on a skateboard with bowling balls providing the reaction mass (normally provided by the rocket exhaust).

When everything is at rest the momentum is 0. (momentum is mass times velocity)

When he pushes the balls back he is giving them some momentum in one direction and gaining some momentum for himself and the skateboard in the other.

The velocity and therefore the momentum in one direction is positive and the other direction both are negative.

The total momentum is still 0 exactly what he started with. It is conserved.

We then considered angular momentum.

Here the mass is rotating and the angular momentum depends on the rate of rotation and the distribution of mass with relation to the center of rotation.

As that distribution is changed the rate of rotation changes so that the total angular momentum is conserved (stays the same).

It is easier to see than to describe.

At one point in the video I said that the student's long arms would result in a big change in momentum when he pulled the weights in.

That is wrong. I should have said that his rate of rotation would increase so that the total angular momentum is conserved.

All the students wanted to try this for themselves, the bell for the end of class rang and they kept coming to try it.

We took a look at a gyroscope and they passed it around.

I like their expressions when it twists in unexpected directions when they tip it.

A top that has a motor powered gyroscope inside demonstrated what they were feeling.

The motion is called precession and is seen at scales ranging from atoms to planets.

When you hold the top you can feel the forces involved.

Gyroscopes are used in satellites to ensure they stay pointed in the direction you set.

And the last video is conservation of angular momentum again, this time the kids talked the teacher into trying it.

In addition to these physics demonstrations we looked at motion and relative motion, acceleration, Galileo's experiment with falling weights, levers, pulleys, the acceleration of a bucket of water in a circle and Newton's analysis of the motion of the moon.

I think you will agree the students enjoyed the lesson and so did I.

To see more of the fun we have had check these links.

Go to our Science Fun page

Go to our Travels page

Go to our Personal home page

Go to our Community page

E-mail Nancy and Alan