Go With The Flow
I'm sure you've seen a jet of water before. You can see the water moving, right?
This experiment is all about making a jet of water where you can't see the movement! Check out this video to see what we mean and then follow the steps below to recreate it.
You Will Need:
Fill a balloon with water until it is about the same size as your bowl. Place the balloon in the bowl so that it doesn't roll around everywhere. Make a # shape with tape - so place two pieces horizontally with about half a centimetre space between them, and then two pieces vertically with the same space between them. The horizontal pieces and vertical pieces should overlap so that a square is left in the middle of the tape. Carefully - ask an adult for help - poke the pin through the balloon inside the square in the middle of your tape pattern. Remove the pin and hopefully you'll have a beautiful arc of water that doesn't look like it is moving! Put your finger in the arc of water to reveal that it is flowing after all!
How does it work?
|Have you ever played Follow the Leader? Water is really good at it because it is a bit sticky. The hole that we made in the balloon with the pin is really small - so the stream of water is thin too. That makes it much easier to follow the leader! Imagine trying to play Follow the Leader in a big crowd - there's always people bumping and shoving against each other so you can't quite move in a straight line following the person in front. With a thin stream of water it is a lot easier.|
The stream of water is actually made up of a huge number of water molecules. These tiny particles - so small that we can't see them even with the best microscopes - all rush and flow whenever water moves. The fact that they can move around each other is why water can flow at all - it's a liquid! You can't get a desk to flow because the molecules in it can't move past each other.
To get the water stream to look the way we want it to - as if it is frozen - all the water molecules need to flow in exactly the same direction. This is where the game Follow the Leader comes in - each molecule of water needs to follow the one in front. When all the flow is lined up like this we call it laminar flow.
For laminar flow we need all the water molecules to be moving in the same direction as they leave the opening and stay together, all organised into a neat stream. There are two things that we need for that to happen: the movement of the water needs to be really aligned as it comes out of the opening and then it all needs to stick together.
We said that water is a bit 'sticky' and that's true but not very technical. What's actually going on is called surface tension and cohesion - all the molecules in the water stick to each other.
The size and shape of the opening we make in the balloon for the stream of water to flow through is crucial to this working. That's how we are going to align the movement up as it comes out of the opening.
More videos about Laminar Flow
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