Physics 2

1. Physics 2 Chapter 11 Sections 1 - 2

2. Internal Energy • Total energy of the particles within a body - depends on the amount of material -depends on the temperature • Internal energy of a material increases when the temp increases and decreases when the temp goes down

3. Heat • Energy in the process of being transferred from one system to another • Heat flows from hotter object to a cooler object • Body doesn’t contain heat – it contains internal energy • Term heat is only used when referring to energy moving from hot to cold or vice versa

4. Caloric • Until the early 19th century the accepted theory was that heat was a type of invisible fluid (called caloric) rather than a type of energy • All objects contained caloric • Caloric flowed from hotter to cooler objects • Caloric could be released when objects were broken down • Caloric was believed to be conserved

5. calorie • Unit of heat • Quantity of heat necessary to raise the temp of 1 g of water by 1 Celsius degree • Calorie (capitalized) is to specify energy in food • 1 food Calorie = 1000 heat calories

6. Mechanical Equivalent of Heat • Discovered by James Joule • Relationship between work energy and heat energy • Discovered that mechanical work can make temp of a substance rise just like absorbing heat • 1 cal = 4.186 J (mechanical equivalent of heat)

7. Sample Problem A worker drives a 0.5 kg spike into a rail tie with a 2.5 kg sledgehammer. The hammer hits the spike with a speed of 65 m/s. If 1/3 of the hammer’s KE is converted to the internal energy of the hammer and spike, how much does the total internal energy increase?

8. Specific Heat Capacity • If Q = heat observations show that Q α ΔT and Q α m so Q α m ΔT or Q = cm ΔT where c = proportionality constant specific heat capacity or specific heat [c] = J/kgC° table of values p 370

10. Sample Problem In a half hour, a 65 kg jogger can generate 8 x 105 J of heat, which is removed from the jogger’s body by a variety of means. If the heat were not removed, how much would the body temperature increase?

11. Sample Problem Cold water at a temperature of 15⁰ C enters a heater, and the resulting hot water has a temperature of 61⁰ C. Suppose a person uses 120 kg of hot water in taking a long shower. Find the number of (a) joules and (b) kcal needed to heat the water. (c) Assuming that the power utility charges $0.10 per kW-h for electrical energy, determine the cost of heating the water.

12. Calorimetry • Using a device such as a calorimeter to measure the quantity of absorbed or evolved heat or to determine specific heat • Calorimeter is an insulated container so total energy doesn’t change heat lost = heat gained

13. Sample Problem The calorimeter cup is made from 0.15 kg of Al and contains 0.2 kg of water. Initially, the water and the cup have a common temperature of 18⁰ C. 40 g of an unknown material are heated to a temperature of 97⁰ C and then added to the water. The temperature of the water, the cup, and the unknown material is 22⁰ C after thermal equilibrium is established. Find the specific heat capacity of the unknown material.

14. Sample Problem What is the final temperature when a 3 kg gold bar at 99⁰C is dropped into 0.22 kg of water at 25⁰C?

15. Sample Problem The air temperature above coastal areas is profoundly influenced by the large specific heat capacity of water. How large of a volume of air can be cooled by 1 ⁰C if energy is transferred as heat from the air to the water, thus increasing the temperature of 1 kg of water by 1 ⁰C? The specific heat capacity of air is approximately 1000 J/kg⁰C and the density of air is approximately 1.29 kg/m3.