I'm always on the lookout for fun and easy science experiments to try with my kids, so when I came across this simple straw fountain, I knew I’d found a winner. You’d never guess by looking at it that this little straw triangle could act as a water pump, capable of spraying water halfway across the kitchen! (Grabbing some towels before you start is definitely recommended.) Silly as this straw fountain is, it actually opens up some really interesting questions about centrifugal forces if you want to take the discussion a little deeper. Or, just let your kids explore and experience some amazing spinning science!
How we did it:
Cut a straw in half. Take one half and use a needle to poke a hole through the middle of the straw. Put a skewer through the hole.
Use scissors to make two slits to the right and left of the skewer, about a half-inch away. Make sure you don't cut the straw all the way through.
Adjust the placement of the straw on the skewer, so the skewer tip and the straw ends all meet at the same point. Use tape to secure the straw ends in place, making sure not to cover any straw openings.
Fill a glass with water and hold the skewer so that the bottom tip of the triangle is submerged.
Tip: Do this part outside or somewhere you don't mind getting a little wet!
With the top of the triangle above water, roll the skewer between your hands and watch your DIY water fountain come to life!
What happens if you spin a little faster or slower? Try making a bigger triangle shape and see what happens!
What’s going on?
Believe it or not, this simple straw fountain works just like many industrial water pumps! Centrifugal pumps use motor-driven spinning blades to fling water radially outward, just like your fountain does. This is just like the behavior of paint in a spin art machine, or water in a washing machine. (Try peeking inside your washing machine while it’s draining — you’ll see the drum inside spinning very quickly, which flings the excess water out of drum.)
The outwards push experienced by the water is called “centrifugal force” — except it’s more accurate to call it a “pseudo force”. You can explore how this works with another pseudo force you’re probably familiar with. Say you’re in a car as it accelerates from zero to sixty — you’ll be pressed back into your seat. If the driver then slams on the brakes, you’ll fly forward. In other words, you get thrown in the direction opposite your acceleration.
It’s the same thing with the water in the fountain. It’s being moved in a circle, so the direction of acceleration is towards the center of the circle. The water experiences a push in the opposite direction, and is flung outwards through the straw — and all over the floor!