Kids will love these inertia science experiments with LEGO bricks!
These activities are a great way to learn about Newton’s first law of motion, which states that an object in motion stays in motion unless acted on by a force and an object at rest stays at rest unless acted on by a force.

Inertia is the term that we use to describe this law. It’s an object’s resistance to a change in motion, or in other words, that object’s tendency to stay either in motion or at rest. Inertia also refers to an object’s resistance to a change in speed, whether speeding up or slowing down. Basically, it takes a force to make an object do something different than what it is doing!

We end up using LEGO bricks as science or math manipulatives all the time. Why buy more school supplies when you can use what you have one hand? And LEGO bricks are so versatile!
Experiment #1: Speedy Takeoff!

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When you’re riding in the car and the driver accelerates suddenly, you feel your body push back against the seat. Why is that? Your body was moving along at a slower speed, and when the car accelerated, your body resisted that change.

Likewise, if you set a drink on top of your car and drive away, the drink is going to want to stay still while the car moves out from under it, giving the appearance of the drink falling backwards.

Let’s demonstrate that with LEGO bricks!

First, build a little cart.

Then make some bricks that can stack. We put a 2 x 4 tile on top of each brick to give the bricks the ability to slide off each other.

The first brick in the stack is attached to the cart.

Give your cart a firm push forward. What happens?

The stack of bricks wants to stay at rest! The bricks stay in place while the cart goes forward. This gives the appearance of the bricks falling backwards.

Note that there is some friction between each brick that causes them to come along with the cart to some extent. But if you give the cart a solid push forward, the bricks will not move forward at the same rate since there is not a force acting on them!

Experiment #2: Big Crash!

This time, we’re going to observe how an object in motion tends to stay in motion.

Build a wall to crash your LEGO cart into.

Then stack your bricks again!

When the cart hits the wall, it stops suddenly. The bricks want to stay in motion, so they topple forward.

Experiment #3: Index Card Flick

We have performed this experiment with an index card and pennies, and we decided to try it with LEGO bricks. It works GREAT!

This is such a clear demonstration of the fact that an object at rest stays at rest unless acted on by a force.

Flick the index card. It will go flying!

But what happens to the bricks? They stay at rest. When the index card is removed from under them, they simply drop into the cup!

It’s fun to experiment with how many bricks you can stack and still get them to land in the cup. We were successful with 5!

Experiment #4: Which Bricks Move?

This experiment is very similar to the last one. If you apply a force to the bottom brick in a stack of bricks, what will happen to the rest?

For our force, we flicked a 2 x 2 round brick at our tower of bricks.

However, instead of just using a round brick, we actually built one with a 2 x 2 round tile and two 2 x 2 round plates. The resulting brick is the same size as a 2 x 2 round brick, but it has more mass. This helped our experiment quite a bit.

Science is so much fun!

More physics science experiments:
Here’s a really fun Transfer of Energy Science Experiment to try with marbles and a wood ruler.

Or use LEGO bricks to make a working Pulley System. This is so cool, and a great way to teach the concept of mechanical advantage.