Jul 9, 2009

Daniel Bernoulli and Robert Plant

This is a little science project toy that I put together for the kids. My background is in physics (and later, design), so I have a huge soft spot for interesting home science experiments. I know the kids at three and four years old are still very young for science, and unlikely to get anything but the most basic concepts, but this project was also a fun toy, so I wasn't forced to wait until they were older (age appropriateness didn't stop me from trying to teach a two year old to say "buckminsterfullerene" to freak people out, when she saw one of the black and white pentagon/hexagon patch soccer balls either)

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:
  1. 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.
  1. 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.
Here are some pics of the kids playing with it and a little video showing it working...




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!

video

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!
video

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!

9 comments:

juliekintaiwan said...

Awesome! Please do more science fun activities ;)

Julie said...

Sweeet! I'm going to have to give that one a try :) Looks like tons of fun!
Keep the cool science things coming! I love it!

Karin Katherine said...

That is so cool! I love this idea. Thanks for sharing it. Science experiments are so much fun with young kids.

Myrnie said...

Very neat project for the girls :) My voice teacher used to pull out pieces of paper all the time, trying to drill into my head that the way to get more sound is to put more AIR between my vocal chords...not to tense them up. (Eek, it sounds bad when they're tensed up!)

BKelly said...

I am a biologist, so I love to sneak science in fun ways to my nephews too. I think my nephew is the only three year old at the Aquarium identifying types of sharks! He loves to come over and feed the "wormins" in my compost bin.
This was a great science activity. Now I think Tessla's birthday was the other day, got any ideas for that one? : ) Keep the science coming, I will have to go find a cereal box and try this one out!

MaryAnne said...

Love this - your explanations of what is going on are great, too!

School for Us said...

I love your scientific explanations - and the activities! Your kids are so blessed to have you for a mom. And, we're blessed by all that you share!

Wolk said...

My first reaction to 'bernoulli' was mostly 'oh GOD, my maths teacher talked about that - RUN!'

Then I read and got flashbacks to my kiddy science book and the actual thing my teacher said to make it clear to us: "The Bernoulli effect is what makes planes fly--and what makes the shower curtain stick to your legs."

tom said...

thAAAnk you for explaining the bernoulli effect so clearly for me, and for the amazing idea for demonstrating it!! i teach outdoor education and have been searching for something like this to add to my kitemaking class. btw cute kids lol