Journal 3/4/16 What is heat? What makes something hot or cold? Objective Tonight’s Homework To learn how we measure and define temperature and heat p 366: 1, 2 p 382: 2

How Do we Measure Temperature? What is heat? How can we measure something like this? We all know ice is cold, but just how cold? Fire is hot, but just how hot? Imagine that thermometers didn’t exist. (Say, back in 1600.) Your job for the next 10 minutes is to come up with a way for how you might measure the temperature of something. You’ll probably have to think up some sort of device with units that you create yourself.

Temperature Scales Like usual, let’s start with history. Until the late 1800’s, the common idea was that heat was stored in every object in an invisible liquid called caloric. Caloric was thought to flow from hot objects into cold ones until both objects had equal amounts. In the late 1800’s, a guy named Count Rumford of Bavaria did some tests to see if this was the way things worked. He found that a lot of things like friction seem to be able to “create” caloric out of nothing. Something was wrong with the caloric theory.

Temperature Scales Eventually, scientists used Rumford’s ideas to come up with the modern theory about heat. We call this the Kinetic Theory. In this theory, heat is generated by atoms vibrating and moving. The more they vibrate, the hotter they are. But we have to be careful with how we define things here. The definition we have so far still doesn’t explain why the air in an oven doesn’t burn you but the metal does.

Temperature Scales We need to explain the difference between heat and temperature. If we take every atom in a substance and add up all the energies from those atoms vibrating, we get a total number. This is a substance’s heat. If we pick an average atom from our substance and look at how much thermal energy it has, we get an average for our substance. This average is temperature.

Temperature Scales Example – burning a log: Once we set our log on fire, we can start measuring how much energy that heat is making. We can get this in Joules. After the log has burned out, we can total up how many Joules the log had in total. This is heat. While it’s burning, we can measure how hot the flame is (how much energy is being made) at any given point. This is the burning log’s temperature.

Temperature Scales So what about our example with the oven? When you touch the air, every atom that hits your skin transfers a bit of energy into your arm. Same with the metal. However, when you touch the metal a lot more atoms touch your skin every second. This means energy goes into your hand much faster when you touch the metal. That’s why you get burned! Note that if you left your hand in the air in the oven, eventually you’d get the same burn. It would just take longer.

Temperature Scales So how do we measure temperature? With something called a thermometer. We’ll go into more detail with exactly how they work a bit later, but for now, all you need to know is that it’s a glass rod with a liquid in it that absorbs this energy from whatever it touches. But to measure something, we have to have a starting point.

Temperature Scales Fahrenheit chose the freezing point of salt water to be 0 degrees and the temperature of the human body to be 100. Celsius chose the freezing point of regular water to be 0 degrees and the boiling point of regular water to be 100 degrees. Lord Kelvin based his system off the motion of atoms and chose 0 degrees to be the point at which at atom would be completely stopped. He made the size of 1 of his degrees the same as 1 degree in Celsius.

Equations C = (F - 32)*(5/9) F = (C*9/5) + 32 K = C C = K – 273 to Celsius to Fahrenheit to Kelvin to Celsius Fahrenheit Celsius Kelvin

Temperature Scales Example: A sample of lava is measured to be 1500 °F. Convert this to both Kelvin and Celsius.

Temperature Scales Example: A sample of lava is measured to be 1500 °F. Convert this to both Kelvin and Celsius. C = (F - 32)*(5/9) C = (1500 – 32)*(5/9) C = °C K = C K= K = K

Exit Question What was the name of the theory that heat transferred between things as an invisible liquid? Temperature Heat Kelvin Caloric Fahrenheit Celsius