Gyroscopes and momentum
Morgan County 7th and 8th grade
A few videos showing a little of the fun we had investigating mass and
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
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
As that distribution is changed the rate of rotation changes so that
the total angular momentum is conserved (stays the
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
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.