Middle school year 1 · sixth unit
Properties of Gases
A gas cannot be seen, yet it makes a ball tight and swells a balloon. That is because tiny particles fly about without rest and hit the walls. Squeeze and heat a gas, and watch what those particles do.
The more air goes in, the harder the ball gets
A board to adjustWhat is going on inside the ball? Pull the pump handle up and push it down to put air in.
A sealed syringe cannot be pushed all the way in
A board to adjustThe further you push, the harder it pushes back. Drag the plunger in and compare pressure with volume.
A dented ping-pong ball pops back in hot water
A board to arrangeHow much does a gas grow when it is warmed? Drag the flask with the balloon into each of the three tubs.
What to take away from this unit
- Gas pressure is the push of gas particles hitting the walls. The more particles, the faster they are and the smaller the space, the more often they hit and the greater the pressure.
- At a fixed temperature, halving the volume of a gas doubles its pressure. Pressure × volume stays the same. This is Boyle's law. A crisp packet swells on a high mountain because the pressure outside is lower.
- At a fixed pressure, the volume of a gas grows at a steady rate as the temperature rises. This is Charles's law. It is why a dented ping-pong ball pops back in hot water.
- When the temperature rises the particles speed up and push the walls harder and more often. So the volume grows (if the wall can move) or the pressure grows (if it cannot).