Why do we wear a seatbelt in the car?


This is how the conversation went:

Allie: “Mommy, do you know why we wear a seatbelt in the car?”

Me: “Why is that Allie?”

Allie: “So we don’t get hurt in the car if we crash.”

Me: “Very good , How did you know that?”

Allie: “Doc McStuffins had a toy alien that didn’t wear a seatbelt in his rocket!”




Leave it to Doc McStuffins to cover that important topic! I thought the conversation would end there, but I didn’t want it to. I wanted to show her in real life. Later that day we were playing outside, and I decided to do a little experiment to drive the point across with a little science. I love these kinds of experiments – they are not messy, and they don’t require much effort.

Question: Why do we wear a seatbelt in the car?

Plan: I wanted to simulate what it would look like by not wearing a seatbelt without injuring ourselves. So, we decided the test subject was going to be one of her favorite stuffed lambs, Santa Lamb.

We used her old tricycle and a jump rope as a seatbelt. We would simulate a crash by gently rolling the tricycle in the garage door. The first test was with a “seatbelt.” The second test was without a “seatbelt.”

Mommy Disclaimer: I told Allie, “Do not perform this test on her little brother, just on Santa lamb.”

Her guess: (This is when I asked Allie what she thought would happen.) Her guess of course was that Santa Lamb would fall off without a seatbelt.

With Seatbelt:

Without a seatbelt:


Why did that happen?: (This is when I attempt to use science to explain the result to her – in her terms.) Santa lamb rolling along on the tricycle has inertia. That’s a big word meaning Santa lamb wants to keep moving with the tricycle, even though the tricycle has “crashed” into the door. When he is wearing a seatbelt, he stays on the tricycle and stops with the tricycle. When he isn’t wearing a seatbelt, his inertia causes him to keep moving, fall off, and bonk his head. A lamb in motion tends to stay in motion.

Follow up: A few weeks later we were discussing Santa lamb and how he should have been wearing a helmet to protect his head. So we performed the test again, but this time Santa Lamb had a custom made helmet, courtesy of Tupperware and some tape.

Helmet with seatbelt:


Helmet without seatbelt:


Categories: 5 minute experiments, lovely conversations, STEM Tags: , , ,