### Expanding prices even more

Anyone that drives anywhere is familiar with paying MORE for gas in the summer. I learned last night that most of us are paying MORE than MORE in the summer, thanks to physics (and lack of regulations in the gasoline industry).

This week I've been experimenting with homemade thermometers. To make one you fill a bottle with room temperature water, add a few drops of dark food coloring and a straw, and seal the straw in place with some clay. The water level in the straw will change in proportion to the temperature of the thermometer's surroundings.

Heat is related to the motion of atoms. The molecules in warm water move faster than those in cold water. This increased motion causes warm water to expand, thereby raising the water level in the straw.

What does this have to do with gas prices???

Well, as Jamie Court pointed out in American Public Media's Marketplace, gas pumps charge us by the gallon, which is a unit of volume. And gas, like water, expands when it gets warm.

Gas companies account for temperature-induced changes in volume when they buy gas from oil companies, but they don't account for it when they sell it to us (except in Hawaii).

This means that a gallon of gas in the summer has less energy than a gallon during a colder time of year. In warmer areas, he figures, people pay on average 3 centers more than the advertised price of a gallon for a standard gallon's worth of energy. This overcharging costs Americans about \$1.7 billion every year.

Of course you get the good end of the deal if you live in a colder climate. Unless you live in Canada, where they temperature-regulate gas pumps.

1. I heard that story too. So I thought I would do some math.

The expansion of gas in the summer costs us \$1.7 billion/year. There are about 200 million privately owned cars in the US.

So the expansion of gas costs us about \$8.50 per year per car.

Is this really a problem?

I'm guessing the cost of pumps that would take account of this would cost a lot more than we would save. Of course that would be passed to the consumer.

-Buzz

2. Good point. But we can't forget that the cost isn't distributed evenly...

Those is warmer climates like CA will pay the bulk of the cost while those in MN probably come out ahead and those in the midwest probably stay even.

Without doing any math, my instinct says it really might be a problem for some people.

3. In your picture with a sealed bottle, the air above the water will expand more than the water - that's what's pushing the water up the straw, not expanding water.

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### Ask a Physicist: Phone Flash Sharpie Shock!

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### The Science of Ice Cream: Part One

Even though it's been a warm couple of months already, it's officially summer. A delicious, science-filled way to beat the heat? Making homemade ice cream.

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Over at Physics@Home there's an easy recipe for homemade ice cream. But what kind of milk should you use to make ice cream? And do you really need to chill the ice cream base before making it? Why do ice cream recipes always call for salt on ice?