The Inertia Paper Napkin Trick

A Peculiar Playdate #12 ∙ Published May 12, 2019

This experiment showcases our old friend, the first law of motion – the law of inertia. Practice it at home in a place where spilled water won’t be a problem. Once perfected, you can entertain guests and kids on the next playdate you host!

What you need

A paper napkin
A glass (or a plastic cup if you don’t want to risk it)

How to make it

Step 1

Drape the napkin over the edge of the table (or at the stack of books in our case)

Step 2

Put your glass on the napkin a couple of inches away from the edge

Step 3

Pull the napkin quickly from underneath the cup!

What happens

If you did it right then what should happen is absolutely nothing! You pulled a napkin, but the cup should stay in one place. If the cup moves and spills, it means you are not pulling fast enough.

Why it happens

As we mentioned earlier, this experiment is based on the law of inertia. The precise wording of this law is this – every object in a state of uniform motion will remain in that state of motion unless an external force acts on it. What it basically says is that things that are at rest want and tend to stay that way, like our glass.

Feathers in exchange for prizes

While working on this playdate idea, our Keedoo Parrot has lost two feathers 😔 Please help us! Collect them by bringing this idea to life with your kids, and we will gratefully exchange them for valuable prizes.

Try making this experiment
Share your experience on Instagram or Facebook
Mention @getkeedoo in comments
Nominate three families to do the same
We will contact you to add three feathers to your Keedoo account that you can exchange for prizes in our mobile app
Follow @getkeedoo on Instagram to see new prizes

Spread the word 🙌