Heat & Temperature. What are heat & temperature and how do they relate?

Transcription

1 Heat & Temperature What are heat & temperature and how do they relate? SPS7. Students will relate transformations and flow of energy within a system. a. Identify energy transformations within a system (e.g. lighting of a match). b. Investigate molecular motion as it relates to thermal energy changes in terms of conduction, convection, and radiation. c. Determine the heat capacity of a substance using mass, specific heat, and temperature.

2 What is Temperature? Quick write activity: (5 minutes) What is temperature? How do you decide what temperature something is?

3 What is Temperature? Some things to think about: How hot is hot? How cold is cold? When we say something is hot or cold, is that a qualitative measure or a quantitative measure? When we say something is 50 degrees Celsius is that a qualitative measure or a quantitative measure?

4 Hot? Cold? Demo Three students will help me with this demonstration. Our procedure will be as follows. Step 1: Put one hand into the cold water. Put your other hand into the warm water. Step 2: Wait one minute. Take your hands out and put both of them in the room temperature water one hand at a time. Step 3: Each student describes the temperatures they felt. Can you rely on your hands to determine temperature? Why or why not?

5 How thermometers work Liquid thermometers work because of. Thermal expansion is the of of a substance due to an increase in. Many thermometers use either or because they remain in the state over a large range of temperatures.

6 Kinetic Energy is the measure of the average energy of particles. Kinetic energy is another way to talk about the amount of movement particles are doing. temperature = more!

7 How thermometers work Imagine this: A dry sponge is our imaginary liquid. The water you add to the sponge would be the heat. When the water interacts with the dry sponge, the sponge expands. The amount of sponge doesn t change, but it spreads apart as it increases in temperature (from more heat).

8 How thermometers work Thermometers are often made of glass with a tiny little glass tube in the center for the liquid to travel. Thermal expansion isn t much for the liquid inside the thermometer, so the size of the inner tube must be VERY small in order to show us the change in temperature

9 Temperature Scales There are 3 temperature scales: (ºF) Most commonly used in the United States Water freezes at 32ºF and boils at 212ºF (ºC) Most commonly used in other countries Water freezes at 0ºC and boils at 100ºC One degree is nearly twice as large as one degree Fahrenheit (K) Commonly used in science Based on absolute zero 0 K is absolute zero

10 Absolute Zero Definition: The temperature at which an object s is. If energy is minimal, is minimal. Can you tell us why? The definition of energy is the ability to cause. Therefore if energy is minimal, motion will be minimal as well. It has been reported that all motion ceases at absolute zero. This is not totally true, but motion does slow to a point of almost stopping.

11 Temperature Scales

12 Temperature Conversion To convert from Celsius to Fahrenheit ºF = 9/5 * Celsius Temperature (ºC) To convert from Fahrenheit to Celsius ºC = 5/9 * (Fahrenheit Temp (ºF) 32.0) To convert from Celsius to Kelvin K = Celsius Temperature Work #1 & #2 on page 328

13 What is heat? is the transfer of energy between objects that are at different. Heat energy is ALWAYS transferred from the object with higher temperature to the object with lower temperature.

14 What is thermal energy? Since heat is the transfer of energy, then is the type of energy being transferred between objects. Thermal energy can move between objects in three different ways.

15 Conduction is simply the transfer of thermal energy through direct contact. Conduction can also occur within a substance.

16 Convection is the transfer of thermal energy by movement of a liquid or gas. The liquid or gas cycles much like a turning bicycle wheel. (Think: Toaster Oven/Oven)

17 Radiation is the transfer of thermal energy through matter or space by electromagnetic waves, visible light, or infrared waves. ALL objects emit radiation. (Think: Sunbathing)

18 Do these items look familiar? Back to Conduction!

19 What do they have in common? All the items in the previous slide are. An insulator is a substance that does not conduct well and reduces the amount of transfer. Substances that DO conduct thermal energy well are called.

20 Conductors ~vs~ Insulators Take a few minutes to create a table that lists some common (household) conductors and insulators Conductor Insulator

21 Specific Heat Defined as the amount of energy transferred as heat that will raise the temperature of 1 kg of a substance by 1 K The abbreviation for specific heat is c. Water has a very high specific heat while other elements are relatively low. Specific heat changes very slightly, therefore we can refer to it as a constant. To calculate the amount of energy it takes to cause a temperature change, we use the following equation: energy = specific heat * mass * temperature change energy = cmδt