Scott Williams, age 10, asked:

I saw a TV show with a guy taking a breath of some gas from a balloon. Helium I think. His voice was funny, like Mickey Mouse. Was it the gas or was he acting?

Prof. Foletta answers:

Scott, he probably was not acting if you heard them say ‘Helium gas’. Helium is the same gas that’s used for blimps. This gas lets the blimp float in the air. That’s because Helium is lighter or less dense than the rest of the gases in air. So a clue to what is happening with the guy's voice is due to the lightness of Helium.

Suppose you move your hand back and forth in big bucket of water as fast as you can. Then you take your hand out and wave it back and forth in the air. Can you wave your hand faster in the water or the air? Well, because air is lighter or less dense than water you can move your hand faster in air. That’s the same reason the guy's voice is higher or funny, because his vocal cords are waving faster in the lighter Helium in his breath.

Why do you think a hot air baloon can float in air?
You can learn more about gases in physics courses and general physics books.

Karen Allen, age ?, asked:

What makes a light bulb light up and why?

Prof. Foletta answers:

Thanks for this interesting question.

A light bulb lights up because someone has just got a great idea (in cartoons only)!

In real life the simple answer for "what makes a light bulb light up" is that electricity flowing through a wire filament, in an incandescent light bulb, heats the wire white hot. The "why" is a little more complicated. I am sure you have used a candle for light. The candle light is produced by the burning wax or heating of the combustion byproducts. When any body is heated its atomic particles are moving more rapidly than when it is cooler. As the wax atoms are heated, some transfer their motion to other material, release energy and cool down. The released energy of the atoms is electromagnetic radiation and is visible to us as light if it is of a certain level. If the energy drop is low we can not see the radiation as light but we feel it as heat (as infrared "light"). If the energy drop is too large we also can not see it as light but it could burn our eyes and skin (as ultraviolet "light").

The tungsten wire filament in the light blub is also heated to a high temperature and so gives off electromagnetic radiation. The heat comes from the collision of electrons (the flow of electricity) with the wire atoms. The wire would also burn if it were not in the glass bulb from which the air has been pumped out and replaced with an inert gas. Even the tungsten wire with its very high melting temperature will melt and the bulb would "burn out" if the temperature gets too high. If the temperature is too low, the light bulb gives off mostly heat and little light. Light bulbs are designed to operate from a given voltage range so that they last a reasonable time and give you white light. If you put your hand close to the light bulb you will feel the low frequency electromagnetic radiation as heat. Most of the radiation from a incandescent light bulb is heat and not light. Other types of lights can produce more light radiation with less heat or wasted energy (such as fluorescent and halogen lights).

Thomas Edison (1847-1931) was the first person to make a practical electrical light bulb. He also invented a number of basic electrical devices that are part of our modern life. Check your library or book store for more information about inventors.

What makes a strobe light flash or a fluorescent light work?
You can learn more about electricity and light in physics courses and general physics books.

Milo Rogers, asked:

What makes water boil?

Prof. Foletta answers:

Water boils if it is heated above a certain temperature. But why and what is boiling? Water and most other molecules and elements can exist in one of three common states: solid, liquid and gas. Boiling is the conversion of a liquid to a gas. The conversion of a substance from one state to another occurs at definite temperatures and pressures.

Water changes from solid to liquid at 32 F degrees and changes from liquid to gas at 212 F degrees at sea level air pressures. Temperature is the measure of relative motion of molecules. Below 32 F the water molecules are locked into restricted motion within the solid ice crystals. Between 32 F and 212 F the more agitated motion caused the molecules to move around in the liquid. Above 212 F the motion is so active that the bond between water molecules is broken and the molecules are free to float away from each other as a gas (steam).

So boiling is the generation of bubbles of gas in the heated liquid. Since the source of heat is usually at the bottom of a container (as with a pot on a kitchen stove heating element), the gas bubbles form on the bottom.

Pressure affects the boiling point of a liquid. If pressure is reduced, the boiling point is reduced. If less molecules of gas over the liquid are striking the liquid surface (lower pressure), it is easier for the liquid molecules to escape or boil out. Food placed in a vacuum chamber can be freeze dried because of this effect. Pressure cookers raise the boiling point of water to help us cook foods faster.

Why do most baking recipes call for more water at higher altitudes?
You can learn more about heat and properties of materials in physics courses and general physics books.
-Prof. Foletta

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