Picture of Floor Cart for Newton's Laws
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


screwdriver or drill with screwdriver bit
allen wrench to fit the roller blade wheels (frequently is included in the packaging for the skates)
Remove these adsRemove these ads by Signing Up

Step 1: Assembling the Base Structure

Picture of 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

Picture of 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.
francests10 months ago

how does the cart "steer" with fixed direction wheels?

CitizenScientist (author)  francests10 months ago
It doesn't, this cart is specifically for one dimensional motion labs.
skidrum3 years ago
Another fun experiment is to pull someone on the cart with a spring-type force gauge, with constant force. The person accelerates, of course, helping visualize N2.
Excellent instructable - well written, clear directions, with great classroom appeal. This would also make a good platform for the classic Wile E. Coyote fan-plus-sail-on-a-skateboard experiment.

At the first college I attended, the Physics 201 class always rode the Library elevators while standing on bathroom scales to study acceleration. We used the data collected to calculate the acceleration/deceleration and maxium speeds of the elevator.
That's an awesome elevator story. I'd love to see that Instructablized.