Nothing helps students understand Newton's Laws and forces better than feeling them! These are instructions for building a pair of floor carts so the students can predict and then test different scenarios involving Newton's Laws. I recommend students wear their bike helmets when using these if they are going to get up to any speed.

Materials for one cart:

8 steel elbows
1 - 3 ft x 3 ft piece of plywood
2 - 3 ft length of 2 x 4
1 pair of the cheapest roller blade style skates you can find (try the clearance isle at your local sporting good store)
16 bolts/nut sets
6 screws
soft rope for handles

Tools:

screwdriver or drill with screwdriver bit
wrench
allen wrench to fit the roller blade wheels (frequently is included in the packaging for the skates)

Step 1: Assembling the Base Structure

Securely screw the two lengths of 2 x 4 to the plywood. The purpose of these boards is to reinforce the plywood where the wheels will be attached.

Use screws that will be flat with the surface so students will not nick themselves on screw heads while riding the cart.

Step 2: Attach the Wheels

Remove the wheels from your cheap roller blade style skates. This is the cheapest way I have found to obtain wheels and bearings with low friction. Save the bolts used to attach the wheels to the skates, you will be using these to attach the wheels to the cart.

Its very important to do this step carefully, and use a T-square to make sure the wheels are perfectly aligned.

Use the right angle brackets to attach the wheels to the cart on the 2 x 4's as shown in the photo.

Step 3: Attach Handles

Drill holes slightly larger than the diameter of the rope to attach the handles for the student to hold on to while riding. Make sure the loop of rope is large enough to fit hands of lots of different sizes.

Now that you have your carts, there are lots of applications for them! The most important thing to do is for students to predict what is going to happen before you try it, and for them to draw the free body diagrams for each situation to explain what happened.

- toss a weight to a student sitting on the cart
- have a student sitting on the cart toss a weight to you
- put weight on one of the carts with a student and have two students put the soles of their feet together and push off of each other
- have a student push off of the wall with the soles of their feet while sitting on the cart

You get the idea!