So, have you heard of the Bernoulli effect? Don't be put off from reading a wee bit more. I swear I'll get to the fun bit shortly. I just want to explain a bit, in case you have older children too and want to explain the principle to them. It's pretty straightforward (if you ignore the mathematics associated with it). Very basically, and to quote an annoying hair care advert... "here comes the science part"...
Air traveling at speed has a lower pressure than stationary air. This wee bit of fluid dynamics results in a lot of interesting, fun and useful things.
I think the most well known application of the effect has to be the aerofoil. The cross-sectional shape of the wing of an aeroplane forces air going over the top of the wing to travel further than that going under the wing during the same space of time, so the air on top is going faster, hence has a lower pressure, so the higher pressure under the wing gives the plane lift.
It's also why you feel pulled towards the track when you stand on an underground station platform and a train goes zooming past you. It's the higher air pressure of the stationary air behind you pushing you forwards into the lower pressure moving air that accompanies the train as it zooms past. If you've ever been in a train with those flip down windows near the roof and as you go through a tunnel they all slam shut violently making everyone in the carriage jump out of their skin, that'll be the Bernoulli effect too. I'll shut up and show you the experiment shall I?
There are several neat ways to show this effect to kids. One really easy one is to just give them two strips of paper to hold, one in each hand and ask them what will happen if they blow between the two flat sheets. Most kids will say the papers will separate and go out away from the space they blow into, because usually things move away when you blow them right? Then get them to try it. In fact the two sheets of paper come together. This is because the blowing creates a tunnel of fast moving air between the sheets of paper and lowers the air pressure between them. The higher pressure on the outsides pushes the sheets in to touch each other.Another great activity for showing this principle to kids is to trap an object (usually a very light ball, like a ping pong ball) in an invisible column of fast moving air. You can do this easily by just popping a ping pong ball on top of the jet of air from a hairdryer. I wanted to make something that my young children could get up close to and explore more easily though, because having a three and a four year old both wanting to hold the hairdryer and having it be waved around in excitement wasn't going to make for much of a contemplative experience.
I gaffer taped a plastic tube to a hairdryer and cut two slits down the tube to fold it in making a cone with a narrow end for the air to blow out, then I cut a hole in a cereal box for the handle and power cord to come out of and closed the box up around it with a hole cut for the cone to poke out of.
Important things to note:
- Make sure you use a hairdryer that has a cold setting! (you might have to tape down a "cold shot" push button to keep it blowing only cold air.
- Make sure you cut a few holes around the base of the box so that air can get in easily to the back of the hairdryer for it to blow out.
So, the column of air coming from the hairdryer is moving fast, hence has a lower pressure than the surrounding air outside of the stream from the hairdryer. When you place the ping pong ball in the stream of fast moving air, it is held there by the higher pressure pushing on it from all around outside the stream. This means you can even tilt the stream of air and the ball will stay in it, which just looks weird and totally freaks the kids out (as you can see from the concentrated slightly confused look on my four year old's face at the end of this video). Magic? No! Science!
We also did a manual version of this experiment with the ping pong balls and blowing into bendy straws. I had to help the kids to place the balls on the end of their straws as they blew, but they were able to keep their ping pong balls floating for a few seconds. I tried to get a breif video clip to show you, but didn't have quite enough hands, so it's only a five second clip!
Just imagine the fun you could have with a leaf blower and a football!!!
I have to go hoover now because someone found a piece of styrofoam and "made it snow" all over the bedroom. Also, I have to deconstruct the Bernoulli demonstration device, because I washed my hair this morning and without the hairdryer I now look like Robert Plant. Baby! Baby! Baby!