1. Ch 6 Thermal Energy

2. Sec 1 Temperature and Heat   As you will find out in PS1, all matter is made up of tiny particles in constant motion   Because they are moving they have KE   The faster they move, the more KE they have   Temperature is the measure of the average KE of the particles in a sample of matter   As the Temp ↑ the particles move faster and their average KE ↑   Temp is measured in kelvins (K), although we use Celsius when working in the lab   One degree of kelivn is the same as one degree of Celsius

3. Temp & Thermal E   Temp is an intrinsic quality: 1 kg of sand has the same Temp as 100 kg of sand—it doesn’t change with the amount   Thermal E (TE) is the total E of the particles in a material—this includes both KE and PE   KE is due to the vibrations/movement of the particles   PE is determined by forces that act between and within the particles   TE is an extrinsic quality: more mass, more TE—it does increase when the mass increases   Different kinds of matter have different TE even when mass and Temp are the same   5g of sand and 5 g of pudding at the same temp have different TE due to how their atoms are arranged   TE depends on the total E of its particles—the KE of the object itself has no effect on its TE   EX. A moving basketball at 20°C has the same TE as one sitting still

4. Heat   Heat--TE that ALWAYS flows from something with a higher Temp to something with a lower Temp   EX -- touch something HOT and heat is transferred to your hand making it warm   Touch something cold and heat is transferred away from your hand making it feel cold   Measured in joules—transfer of E—just like work   Now explain: How does the cooling occur when you put ice cubes in your drink?

5. Measuring TE   Different materials need different amounts of heat to produce similar changes in their Temp   EX Out at the lake the air Temp is 36°C (HOT!) and you are hot and sweaty and decide to go for a swim so you jump in the lake and the water seems VERY cold even though it has been sunny all day   Water requires a lot more E to change it’s Temp compared to air and other substances   This amount of E is called the materials SPECIFIC HEAT—C p – amount of E required to raise the Temp of 1 kg of material 1 degree kelvin   Copy the chart on pg 161 onto your Physics Hand-out (add Al= 920J/kgxK)   As you can see, water requires more E to raise its Temp 1 degree K, but iron is much less—metals heat up very quickly

6. Measuring TE cont.   You can’t measure TE directly like you can Temp with a thermometer, but you can use C p to measure changes in TE   Q = m x ΔT x C p   Q= change in TE   m= mass   ΔT= change in Temp (T f - T i )   C p = specific heat   ΔT→positive→increase in Temp→heat gained   ΔT→negative→decrease in Temp→heat lost

7. Let’s Practice!   A 3.1 kg ball of Al foil cools from 30°C to 15°C. What is its change in TE?   1. Q = m x ΔT x C p   2. m = 3.1 kg ΔT = 15°- 30° C p = 920 J/kg x K   3. Q= 3.1 x (-15°) x 920 J/kgxK   4. Q= -42780.0J   The Al foil ball loses 42780.0 J

8. Whiteboards!   If a 45 kg brass sculpture gains 180,480 J of TE when its Temp increases from 28°C to 40°C, what is its approximate C p ?   A 55.0 g iron nail has been heated to 90°C, then cooled to 25°C. What is the change in TE?   How much TE does a 420 g of liquid water gain when it is heated from freezing point to boiling point?   50.0 g of water and 50.0 g of sand each absorb 200 J of solar E. What will the Temp change (ΔT) of each material be?