Pressure and Heat
Today, Mr. Fong used ice to boil water.
Today I learned:
The air pressure around us has a lot to do with the boiling point of the water. When the air pressure is high, there is more pressure that is holding the water molecules down. But the lower the pressure, the easier it is for the water particles to escape. That means that the it is easier for water to boil.
Today’s experiment:
- Fill flask with water.
- Boil water until bubbles, water vapour appear.
- Quickly cap on lid, to prevent water vapour from escaping.
- Turn flask upside down.
- Place icecubes on top of flask.
- Observe boiling water.
Water in all three states side by side
The ice on top of the flask takes heat away from the warm water vapour at the top of the flask. As the water vapour cools, it condensates and becomes water. That means that there is less water vapour, and a lower pressure. As explained above, lower pressure means lower boiling point. The water is already quite warm (almost boiling), so it boils at the new lower boiling point.
Boiling a pot of water works best when heat comes from the bottom. This is because of convection. When water is heated, it tends to go upwards as it is lighter than cool water. This circulates the water, so the cool water now is at the bottom to be heated. If the heat source was at the top, the top water would be warmed, but it would stay and the top, so it would only get warmer.
Today I wondered:
Does gravity affect the boiling point of water? If particles are so susceptible to forces that hold it down, maybe gravity does too.
How does the drinking bird work? It seems very efficient in its energy conversion.
Today I had an intriguing idea:
If the drinking bird is so efficient at going up and down, perhaps it’s energy can harnessed for electricity. I’m not sure if it would work on a large scale to turn a turbine, but it could potentially provide lots of energy.