Conservation of Momentum

Objects in Motion, Chapter 5 part 1, Conservation of Momentum.

I turned to a favorite book of mine, Gizmos and Gadgets, and found a bunch of activities relating to this chapter. Simple things, like giving them three coins--two pennies and a nickle--and challenging them move one penny using the other penny without them touching each other. They tried all kinds of things before finally figuring out how to use then conservation of momentum to do it.


And more complex things, like creating Newton's Cradle using marbles and an egg carton ramp. There's just something fascinating about watching spheres collide!

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We finished up building a simple momentum tower, another idea from the book. I had two 20 oz bottles filled with water. The kids tied a string between them and then attached two strings with paperclips to the first string, and then stuck modeling clay onto the paperclips. They held the bottles so the string between them was taut and then carefully swung only one of the clay suspensions. Guess what happened to the other clay swing?

Universal Gravitation

Objects in Motion, Chapter 4, The Law of Universal Gravitation.

This chapter brings together Kepler, Galileo, and Newton, especially the first and the last.  I created a review sheet listing their laws we covered next to a picture of each of them.

All I used for this class was a white board.  I read and we discussed, using the board to draw illustrations and to write equations.  It served as a good opportunity for review as well as an opportunity to consider the information in novel circumstances.

We considered and discussed the weakness of gravity, elliptical motion, "falling around" earth, wobbling planets, Newton's cannon, and satellite rockets.  It makes for good conversation...

Laws of Motion

Chapter three of Objects in Motion is Newton's Three Laws of Motion.  I collected several different demonstrations for this class, and thanks to The Happy Scientist, we demonstrated all three with a scale and some hand weights.

I created a worksheet so they could fill in all the different demonstrations we did during class.  I did a demonstration and then read from the book, did another demonstration, and so forth.

The First Law is that of inertia.  I placed a baseball card on top of a glass, and then stacked coins on top of the card.  I asked them to predict what would happen to the coins when I horizontally flicked the card away (they said the coins would fly off everywhere.)  Of course they dropped into the glass, and I let them try it a few times.  I also gave each of them some thick paper (bookmarks, actually) and a stack of pennies.  I instructed them to place the bookmark on the edge of the table so half of it was off of it and then to put a stack of coins on the bookmark.  They quickly pulled the bookmark out from under the coins and the stack remained intact on the table.  (The boys, of course, experimented with ways to make the coins spill...)

Another demonstration we did used a wheeled cart and a stuffed animal.  Shoving the cart made the toy fall off the back; stopping the cart suddenly made the toy fall forward.  We discussed the usefulness of seatbelts.

Finally, we wrapped up with The Happy Scientist: Newton's Laws that demonstrates all three laws in one activity.  You do not need a subscription to view this particular file, but I highly recommend it.  For $20 a year you get a wealth of videos, experiments, and science information.  Robert Krampf does a great job, and many of his videos are quite funny as well as interesting and informative.  All you need is a bathroom scale--the type with an analog display (digital won't work)--and a heavy object (hand weights work well.)  The kids are fascinated with how the scale changes as the weights are rapidly pushed up or pulled down.  Simple yet impressive!

Towers and Parachutes

Week 3 introduces us to the famous legend of Galileo dropping objects from the Tower of Pisa.  We completed the student exploration guide of the ExploreLearing Free Fall Tower Gizmo.  Another free tower simulator, Galileo Drops the Ball, and many other science simulators are available from SEED.

Before starting the Gizmo I gave a simple demonstration.  I took a feather and a ball and asked which would fall faster; then I dropped a small toy and a large toy.  Some were surprised that the second set of objects hit the ground simultaneously.  Next I dropped a book and a sheet of paper, and they fell at different rates.  Finally, I placed the sheet of paper on top of the book and dropped them; they fell at the same rate.  That got them thinking about concepts that they could explore further with the Gizmo.

After learning about air resistance, terminal velocity, and vacuums, I gave the 3 physics groups a challenge.  They each needed to build an egg parachute that met two criteria.  First, the egg had to fall without breaking; second it had to fall more slowly than a rock dropped simultaneously.

Each of the three groups were all successful, and had very different designs.  The older boys used a large sheet of newsprint for the parachute and a thick cardboard cone to hold the egg.  It's a good thing it didn't rain that day...

The girls covered fabric with lamination, adding in straw stays for the parachute and along the strings; they had a foam cube for the harness, decorated with flowers.  It fell the fasted of the three, but still slower than the rock.

The younger boys used a trash bag for a parachute and a cut up egg carton for the harness, with a good amount of duct tape to hold it all together.

I gave them two weeks for construction.  The day of the drop was very windy.  All the kids (21 of them) gathered for the event.  You can see the videos of each parachute being dropped out a window, a team member dropping the parachute and an adult dropping a rock.

Pendulums

Our third week of co-op we performed the pendulum experiment described in the book.  We had three fishing weights (labeled 1, 2, and 3), three lengths of string, and a stopwatch. I created a data sheet (link goes to Google Docs) for them to fill in; they will need three of them to record data for the entire experiment.

This is one experiment in which the kids are very much surprised by the results.  They expected that lifting the weight higher up would increase the time for 10 swings; they also expected a heavier weight to make a difference.  Only the length of the string matters.

Related Gizmos:  Period of a Pendulum and Pendulum Clock