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June 24, 2010
10 notes
We talked about how there is a lowest possible temperature, and that it’s absolute zero: -273 °C. You may wonder: how did they discover that? They must have had a bunch of fancy equipment and huge rooms full of machines to achieve low temperatures, right? No. They couldn’t get anywhere near absolute zero when they discovered it. (Even though now we can, and yes you have to have lots of fancy equipment.) What they did was realized that PV=nRT was a good relation between properties of a gas. Think about this: what if P became 0 in that equation? Then T would also have to be zero. So a gas in a pure vacuum will have zero temperature. Well, a pure vacuum doesn’t really exist, because if the gas is there, then there can’t be a pure vacuum. But this is still useful, because what they did is measured the P of several gases at 2 T values. That’s easy enough. Then you notice that they all extrapolate back to the same “zero” temperature. This is absolute zero. Lots of people in the history of science contributed to this, but Joseph Louis Gay-Lussac was the first person (in 1802) to use the number -273.

We talked about how there is a lowest possible temperature, and that it’s absolute zero: -273 °C. You may wonder: how did they discover that? They must have had a bunch of fancy equipment and huge rooms full of machines to achieve low temperatures, right?

No. They couldn’t get anywhere near absolute zero when they discovered it. (Even though now we can, and yes you have to have lots of fancy equipment.) What they did was realized that PV=nRT was a good relation between properties of a gas. Think about this: what if P became 0 in that equation? Then T would also have to be zero. So a gas in a pure vacuum will have zero temperature.

Well, a pure vacuum doesn’t really exist, because if the gas is there, then there can’t be a pure vacuum. But this is still useful, because what they did is measured the P of several gases at 2 T values. That’s easy enough. Then you notice that they all extrapolate back to the same “zero” temperature. This is absolute zero.

Lots of people in the history of science contributed to this, but Joseph Louis Gay-Lussac was the first person (in 1802) to use the number -273.

Tags: science temperature chemistry physics ideal gas absolute zero

Photo
June 23, 2010
22 notes
To consider absolute zero, let’s mention an ideal gas. If you’ve ever taken chemistry, you’ve probably heard of something called an ideal gas. An ideal gas is a simplified model to describe how gas molecules act. It treats them as essentially like billiard balls. So if you’ve played pool (or taken physics) you’ve got a handle on that. (BS Alert: they’re like billiard balls with zero size. But we digress …) The equation you derive for this is PV=nRT, which kind of shows you that “pressure and temperature of an ideal gas are proportional to each other.” If T goes up, P goes up. If you don’t like math or equations, you can still totally understand this: Temperature makes the balls move faster Pressure is cause by them hitting the walls of the box they’re in So, totally non-math: if they go faster, they hit harder. Easy, right? If T goes up, P goes up.  Don’t do this, but if you throw an old canister in a fire it will explode. Because the billiard balls inside go so fast they blow the canister open. (And the billiard balls are the gas molecules, like air molecules.)

To consider absolute zero, let’s mention an ideal gas. If you’ve ever taken chemistry, you’ve probably heard of something called an ideal gas. An ideal gas is a simplified model to describe how gas molecules act. It treats them as essentially like billiard balls. So if you’ve played pool (or taken physics) you’ve got a handle on that. (BS Alert: they’re like billiard balls with zero size. But we digress …)

The equation you derive for this is PV=nRT, which kind of shows you that “pressure and temperature of an ideal gas are proportional to each other.” If T goes up, P goes up. If you don’t like math or equations, you can still totally understand this:

  • Temperature makes the balls move faster
  • Pressure is cause by them hitting the walls of the box they’re in

So, totally non-math: if they go faster, they hit harder. Easy, right? If T goes up, P goes up. 

Don’t do this, but if you throw an old canister in a fire it will explode. Because the billiard balls inside go so fast they blow the canister open. (And the billiard balls are the gas molecules, like air molecules.)

Tags: science temperature chemistry physics ideal gas

Photo
June 22, 2010
28 notes
Hello Clear Scientists. Let’s talk about something suggested by a Clear Science reader. What exactly is absolute zero? How do they measure it? It turns out temperature has a minimum value, which is absolute zero. Temperatures below this value cannot exist. Absolute zero is -273 °C (which is also -459 °F). In science, we never use Fahrenheit degrees to measure temperature, even in the United States. (This makes your scientist brain kind of split off from your regular brain—for example, the Clear Science staff works exclusively in Celsius, but if you ask us what a comfortable Celsius temperature is, we still have to do the math to convert 72 °F and find 22 °C.) For some scientific work, it is critical to have another temperature scale where absolute zero really means zero. We call this temperature scale the Kelvin scale. You calculate it by adding 273 to the Celsius temperature—this shifts -273 up to 0. A comfortable temperature in kelvins is 295 K. By the way, you say “kelvins” and not “degrees kelvin.” Did you know that?

Hello Clear Scientists. Let’s talk about something suggested by a Clear Science reader. What exactly is absolute zero? How do they measure it?

It turns out temperature has a minimum value, which is absolute zero. Temperatures below this value cannot exist. Absolute zero is -273 °C (which is also -459 °F).

In science, we never use Fahrenheit degrees to measure temperature, even in the United States. (This makes your scientist brain kind of split off from your regular brain—for example, the Clear Science staff works exclusively in Celsius, but if you ask us what a comfortable Celsius temperature is, we still have to do the math to convert 72 °F and find 22 °C.)

For some scientific work, it is critical to have another temperature scale where absolute zero really means zero. We call this temperature scale the Kelvin scale. You calculate it by adding 273 to the Celsius temperature—this shifts -273 up to 0.

A comfortable temperature in kelvins is 295 K. By the way, you say “kelvins” and not “degrees kelvin.” Did you know that?

Tags: science temperature kelvin