But this fun and simple experiment is a great hands-on demonstration. Kids love watching the straw dancing and bobbing around and it’s a great activity for strengthening hand muscles as they squeeze the bottle as hard as they can, to move the straw up and down.
YOU WILL NEED:
An empty soda bottle with the label removed (you need to be able to see inside!)
A small amount of play dough, plasticine or clay
HOW TO DEMONSTRATE AIR PRESSURE TO KIDS:
1.Cut a small length of straw
2.Plug one end of the straw with the play dough
3.On the opposite end of the straw, make a ring of play dough around the outside of the straw (so the straw is weighted but is open at that end)
4.Fill the bottle three quarters full with water
5.Drop the straw into the bottle and screw on the lid
6.Now to the fun part!
Squeeze the bottle as hard as you can and watch what happens……
The straw will sink!
WHAT IS AIR PRESSURE?
So what is air pressure and what’s actually happening here? When you drop the straw into the bottle, the air inside it makes it float. When you squeeze the bottle, the space inside is compressed, that is, there is less space for the air to circulate so the pressure inside the bottle increases. This pushes water up into the straw, making it heavier, so it sinks. When you release the pressure on the bottle, the air pressure decreases (ie the air has more space to move around) so the air fills the straw again and the straw floats back to the top of the bottle.
TIP: If your straw is not sinking try squeezing the bottle at the top where there is no water. Also try lifting the bottle off the table when you squeeze.