Skip to content

Anyone in your family interested in cars and physics? Even if you don’t realize it, working with the first thing can teach you a lot about the second. Today we’re going to look at Newton’s Three Laws of Dynamics using toy cars.


  • A few blocks or books
  • A few toy cars that roll
  • A small action figure or doll, or a smaller block or penny that can ride on the car
  • Piece of cardboard big enough to use as a ramp (older children can use wood)
  • Marbles
  • Plastic eggs

1.    Newton’s first law states that an object at rest stays at rest, and an object in motion stays in motion, unless acted on by an external force.

To test the object at rest part, place a small block or action figure/doll on a car (even a penny will work). Push the car, taking care not to push the object resting on it. Usually the block or doll will “stay put” by falling off, or at least falling back, while the car rolls away.

Now roll the car with the block or doll riding on it towards a barrier, such as a book or larger block. When the car hits the barrier, what happens to the rider? Does it fly forward? The rider is trying to remain in motion even after the car stops.

A child may wonder why, if an object does indeed remain in motion, does the car eventually stop rolling? Think of some other forces acting one the car that we might not see. How would you test this?

2.    Force equals mass times acceleration F=ma

Toy cars and ramps

Raise a piece of cardboard on books, blocks or a piece of furniture. Roll cars of different sizes and weights down the ramp, or add weights to cars of the same size (you can tape on pennies). Do bigger cars go farther and/or faster?

Now push the cars rather than simply letting them roll. See any difference?

Older children can actually calculate the force by weighing the cars and timing them.

3. For every action, there is an equal and opposite reaction.

Most children are more than willing to crash their toys cars into each other to test this theory.

You can save wear and tear on the vehicles by creating demolition derby vehicles out of the bottom of a plastic egg and a marble. You can decorate the egg with a sharpie marker. Place a marble under the egg and roll it away. See what happens if you add smaller, larger or more marbles under the egg. What happens when two plastic egg racers crash?

plastic egg marble car


NASCAR Physics for the Older Set
The Science of Speed is a series of 13 videos at that relate physics to what you see on a NASCAR race track. Just click on the circles under the “Science of Speed:” text to navigate through the videos. Topics include drafting, tire pressure, and friction and heat. Note: there are car crashes.

Thanks to Karen of Leaping From The Box for contributing the NASCAR link. If you are a NASCAR fan, try her racing blog.

For more info:

Teaching Physics with Toys: Activities for Grades K-9 by Beverley A. P. Taylor, James Poth, Dwight J. Portman

(Amazon Affiliate Link)

Continuing with the floating/boats theme we’ve had in previous posts, you just have to see this video:

What do you think? Are you ready to grow a giant pumpkin and give it a try?

Have a fun Friday!

Edit: Check this post for Why Pumpkins Float

Do you remember the challenge, to propel a homemade boat across a bathtub without using your hands to touch it, batteries or electricity? We came up with six ways to do this. Did you come with any that we didn't? Let us know!

1.    Wind or air movement
Probably the most obvious way to propel a boat without touching it is to use air movement or wind. We tried both creating a sail and blowing on it and also using a fan to create air. Both were effective, although somewhat slow and hard to steer.

2.    The classic balloon boat –

You may have seen instructions for these or tried out a kit. I found some available for sale on the Internet (see Resources below) or you can make your own. Check these fun instructions to build a balloon boat from ZOOM, the PBS TV show.

Note:  Please be careful using balloons, and always have adult supervision. Children under 8 years can choke or suffocate on uninflated or broken balloons.

3.    Wind-up propeller
My son took a wind-up propeller from a balsa wood airplane and modified it to propel a flat wooden boat. The stretched rubber band creates the potential energy which is then transferred to kinetic energy. It is fast for short distances.

See the red propeller on the right, rubber band across the center and nail holding it on the left.

4.    Magnet Repulsion
Okay this one was my idea. I remembered moving train cars in a wooden train set by reversing the magnets. It works with an egg carton boat, too. I think this type of boat has the best steering once you get the hang of it.

Here is a short video showing one of our trials. Bear with us, we're still learning video technology 🙂

5.    Detergent Power / Soap propulsion

You may have seen instructions for a soap boat that actually moves. We created one using a top of a Styrofoam egg carton and a squirt of dish detergent. This is not technically a chemical reaction, the movement has to do with the surface tension of the water.

Instructions for a soap-propelled boat from CSIRO.

We simplified the technique a bit by just adding the dish detergent to an egg carton boat and it still seemed to work.

6.    Chemical reactions

My dad told me that as a kid he had a boat that ran on Alka Seltzer tablets. You can also make boats propelled by baking soda and water, or vinegar.

ZOOM has instructions for a Soda Bottle Boat

Good luck and I hope you try some of these. They were fun and we learned a lot too.

Resources for Further Explorations (Affiliate links to Amazon):

Balloon Powered Wooden Boat

Rubber Band Paddle Boat

Let's Try It Out in the Water : Hands-On Early-Learning Science Activities by Seymour Simon, Nicole Fauteux, Doug Cushman (Illustrator)

Teaching Chemistry with TOYS by Jerry Sarquis, Mickey Sarquis , and John Williams

Science in Seconds with Toys: Over 100 Experiments You Can Do in Ten Minutes or Less by Jean Potter

Magnetic Boats in the Tub