Fill a pot with water, put it on the stove, turn the stove on high and then watch and listen. When you are done come back and read the rest.
I'll wait. Don't worry..
>waiting patiently<
>twiddles thumbs<
Oh, even though you are watching it, the water will still boil.
>Sigh. Me thinks you shouldn't have put so much water in the pot. Seems to be taking too long!<
Phew, I'm glad it finally boiled. So what did you notice?
Notice "air bubbles" forming at the bottom? Well, I hate to admit it, as a kid I always thought it was air sneaking in. The bubbles are really just liquid water turning into a gas.
Did you notice the bubbles disappearing when they started to float up? This has to do with energy transfer.
The temperature of an object is a measure of the average kinetic energy or basically the speed of the molecules in the object, in this case, water molecules. So when you add heat to the bottom, the molecules on the bottom get the energy first. Sometimes they have enough energy to become a gas. If enough of these molecules come together a gas bubble forms. If the bubbles are big enough, they will start to float up after breaking the surface tension holding them to the bottom .
As they rise, they come in contact with colder/slower moving water molecules. These gas molecules can lose enough energy that they become "liquid" again and the gas bubble collapses. The collapsing bubble create the hiss that you hear. As more heat is added eventually the gas bubbles make it all the way up to the top, because they don't lose enough energy as they rise, the gas "escapes". The bubbles never collapse so the hissing stops and a boil soon develops.
One of the interesting aspects of energy transfer is that different materials transmit energy at different rates. Fibre glass insulation is a poor conductor of heat so it is used to keep the house "warm" during the winter. Some materials are excellent conductors of heat. One of the substances is liquid helium. It is a VERY cool substances, I mentioned this before here near the bottom of the post. Liquid helium is a super fluid in certain conditions. One of the properties of a super fluid is that energy is transmitted VERY quickly throughout the fluid so no bubbles get a chance to form. In one of the series of clips here, it shows the transition from a "normal" liquid to a super fluid state. In the second video of the 5 segments, at the 4 minute mark (a good explanation continues until the 5 minute mark), it shows liquid helium going from "boiling" to not boiling. This represents when the energy in liquid helium gets transferred away almost immediately.
You must admit, UGOTTALUVPHYSICS!!
