1. Physics Unit 5: Heat and Temperature

2. Temperature What does temperature indicate?
Measurement of the average Kinetic Energy of the molecules
NOT A MEASURE OF HEAT

3. Measuring Temperature
We use a Thermometer to measure temperature
Thermometers rely on expansion
Most objects expand when their temperature increases
Alcohol or Mercury Thermometers use expansion and contraction to measure temperature.

4. Digital thermometers use electrical current to measure temperature.
The warmer a liquid is, the more the particles move and thus they expand (take up more space) and rise up through the tube
Liquid thermometers can only be used between certain temperatures, why?
Because the liquid will freeze at low temps
Because the liquid will boil at high temps
So, some thermometers use a solid metal to measure temperature through expansion
Like a metal coil used in refrigerators
Digital thermometers use electrical current to measure temperature.

5. Temperature Scales There are three temperature scales
1) Fahrenheit Scale: water boils at 212 oF and freezes at 32 oF, normal body temp is 98.6 oF.
2) Celsius Scale: like the metric system, it is bases on powers of 10.
- water boils at 100 oC and freezes at 0 oC.
3) Kelvin Scale (Science): water boils at 373 K and freezes at 273 K. (no degree symbol b/c it does not vary or change based off of location)
- absolute zero (0 K): motion stops…the lowest possible temperature you can go. (-273 oC)
The size of each temperature unit or degree for the Celsius and Kelvin unit is the same. The difference between the boiling point and freezing point for both is 100.
The size of the Fahrenheit degree is smaller that the Celsius degree. The diff between the boiling point and the freezing point ( ) is 180 degrees, not 100 like Celsius or Kelvin.
The zero points are all different on all three scales.

6. Since the Celsius and Fahrenheit Scales can go below their zero mark, they have negative values.
This is why they are reported in degrees
Since KELVIN starts at zero, and cannot go below that absolute zero, then you cannot have negative Kelvin
This is why Kelvin is not reported in degrees
Kelvin is always positive

7. Converting Temperature
Celsius to Kelvin: tK = t oC
Ex: 23 oC to K
Kelvin to Celsius: t oC = tK
Ex: 338 K to oC
Celsius to Fahrenheit: t oF = 1.8 (t oC) + 32
Ex: 33.5 oC to oF
Fahrenheit to Celsius: t oC = (t oF – 32) Ex: 147 oF to oC
The size of each temperature unit or degree for the Celsius and Kelvin unit is the same. The difference between the boiling point and freezing point for both is 100.
The size of the Fahrenheit degree is smaller that the Celsius degree. The diff between the boiling point and the freezing point ( ) is 180 degrees, not 100 like Celsius or Kelvin.
The zero points are all different on all three scales.

8. Temperature and Energy Transfer
When you hold an ice cube, the ice melts because of the energy transfer.
The particles of your hand are moving faster than those of the ice cube
The particles of your hand collide with the particles of the ice cube and cause the particles of the ice cube to move faster
When the ice cube particles move faster (higher kinetic energy) from this collision, the temperature of the ice cube rises and thus it melts.

9. This happens until equilibrium is reached!
The energy transfer between particles of two objects due to a temperature difference between the two objects is called heat.
The transfer of heat ALWAYS goes from higher temperature (faster moving) to lower temperature (slower moving)
This happens until equilibrium is reached!
A seat may feel cool at first, but your body will warm it up until they reach the same temperature (equal temp equilibrium)
Heat gained = heat lost
Law of conservation of energy

10. Methods of Energy Transfer
Conduction: involves objects in direct contact
Fast moving molecule will collide with slow moving molecule, transferring energy
Works for all 3 phases of matter
But gases are very poor conductors because the particles are so far apart
Liquids are okay
Solids are best insulators, but vary by substance
Heat Conductor: Substance that moves heat more effectively (like metal skillets used to cook)
Insulator: Substance that will not conduct heat well (like fiber glass insulation, wood on skillet handle)

11. 2. Convection: movement of warm fluids
The fluid (air) transfers the heat
Molecules move in currents
Only in a fluid: (Liquid or Gas)
Heated portion speeds up and becomes less dense, creating a current of heat
Air currents are a result of convection

12. 3. Radiation: does not require direct contact
Heat is transferred through space
Does not involve the movement of matter
Travels as waves
Electromagnetic radiation (Gamma, UV, Visible, X-rays, Microwaves, Radio, Infrared,)

13. Measuring Heat calories (cal) or joules (j) are used to measure heat
calorie: Amount of heat needed to raise the temperature of one gram of liquid one degree Celsius
Since heat is related to kinetic energy, the unit of joules are often used
1 cal = 4.2 joules

14. What Are Food Calories? Calories are really kilocalories
2000 Cal diet is really 2,000,000 calories
We use capital C (kilo) because it is easier

15. Specific Heat (s) :
Specific Heat (s) : amount of energy required to change the temperature of one gram of a substance 1 oC
How well a substance conducts heat
Varies from one substance to another
Heat always travels from high concentration to low concentration!!
Heat lost = Heat gained

16. Water has a specific heat = 1 cal/goC or 4.184 J/goC
Water has the second highest specific heat capacity of all known substances. So it requires high amounts of heat energy to raise water temperature.
water also has a high energy/heat requirement for evaporation
SIRON = J/goC
Which would heat up faster, 5.00 grams of iron or 5.00 grams of water?
  Which would cool down faster, 5.00 grams of iron or 5.00 grams of water?
 Which is a better thermal conductor?
 Which is a better insulator?

17. Q = s x m x DT Q = energy (heat) required (J) or (cal)
s = specific heat capacity (J/goC) or (cal/goC)
m = mass of the sample in grams
DT = change in temperature in oC
A 2.8 g sample of a pure metal requires 10.1 J of energy to change its temperature from 21 oC to 36 oC. What is the specific heat of the metal?
s = Q = J = J/goC m x DT (2.8 g x 15oC)

18. Applications Heating Systems:
Work can increase ave kinetic energy, like when lighting a fire by using the friction of two sticks
Our bodies act like a heating system to regulate our body temp to stay at 37 oC or 98.6 oF, we burn stored calories and nutrients to provide the energy we need to raise our temp in the cold.
The sun can be used to heat a system
by cold-blooded animals to help maintain their temp

19. Cooling systems:
Liquids can be evaporated or condensed to allow for transfer of energy in either direction so as to cool or heat a system.
Evaporation causes a cooling effect because gases are farther apart and thus cannot transfer energy as well through physical contact