Journal 12/1/16 Objective Tonight’s Homework What’s the hottest thing you’ve ever touched? What’s the coldest? Objective Tonight’s Homework To learn about how we measure temperature p 247: 1, 2, 3

Heat Expansion and Temperature Scales Look at a sidewalk. You’ll notice the concrete has been divided into blocks. Why?

Heat Expansion and Temperature Scales Look at a sidewalk. You’ll notice the concrete has been divided into blocks. Why? If you compare summer to winter, the answer becomes obvious. The gap or groove between blocks is much smaller in summer than in winter.

Heat Expansion and Temperature Scales You’ll see this same effect in other objects as well. Does anyone have a house door that has trouble closing in the middle of summer? Or a ring that doesn’t fit as well in summer? All these things are examples of what we call heat expansion. So our next question follows naturally: Why do things physically expand bigger in heat?

Heat Expansion and Temperature Scales Everything is made of atoms. As we increase the temperature of an object, the atoms it is made of move faster and push apart more.

Heat Expansion and Temperature Scales This idea is behind how we measure temperature. Imagine we take a strip of metal. We attach that metal to something like wood (which doesn’t change size much from temperature). We then place this object in something like freezing salt water. We note the height of the metal and decide to call this “zero”.

Heat Expansion and Temperature Scales This idea is behind how we measure temperature. Imagine we take a strip of metal. We attach that metal to something like wood (which doesn’t change size much from temperature). We then place this object in something like freezing salt water. We note the height of the metal and decide to call this “zero”. We then place this device in something else, (like a human mouth) and measure again. We call the new height of the metal “100”. 100

Heat Expansion and Temperature Scales What have we just created? Essentially, we’ve done the same thing Fahrenheit did, but with metal instead of liquid. The Fahrenheit thermometer used a thin tube filled with mercury. As the mercury heats up, it expands in the tube, rising to a higher level. Fahrenheit defined 0 and 100 the way we just did. There’s another scale, too. Centigrade. This method of measuring temperature works the same way but with a different scale. It uses the freezing and boiling of regular water for 0 and 100 instead.

Heat Expansion and Temperature Scales There’s one more scale, though. Scientists use a system called “Kelvin”. This is just like the Celsius scale but shifts everything up by 273.15 degrees. This lines up “0 Kelvin” with the scientifically coldest possible temperature. This “lowest temperature” is called “absolute zero” and is defined as the temperature you get when all atomic motion in an object stops.

Heat Expansion and Temperature Scales C = (F – 32)(5/9) F = (9/5 C) + 32 K = C + 273.15

Converting Temperatures Copy down and fill out the rest of the table below: Fahrenheit Celsius Kelvin 100 K 212 °C - 50 °F 0 °F 5,000 K 300 K - 459 °F 0 °C 312 °C 98.6 °F - 200 °C 541 K

Exit Question Concrete, asphalt, and metal are known to expand quite a lot. As such, you’ll see what the image shows on any bridge. It’s called an “expansion gap”. With what we’ve learned today, what time of year was this picture taken? a) Summer b) Fall c) Winter d) Spring