1. I. Energy and Work Energy Work Conservation of Energy
Ch. 5&6 - Energy
I. Energy and Work
Energy
Work
Conservation of Energy

2. A. Energy ENERGY THERMAL The ability to cause change. MECHANICAL
internal motion of particles
ENERGY
MECHANICAL
NUCLEAR
motion of objects
changes in the nucleus
ELECTRICAL
joules (J)
CHEMICAL
motion of electric charges
bonding of atoms

3. A. Energy Kinetic Energy (KE) energy in the form of motion
depends on mass and velocity
80 km/h
50 km/h
Which has the most KE?
Which has the least KE?
80 km/h truck
50 km/h motorcycle

4. A. Energy Potential Energy (PE) stored energy
depends on position or configuration of an object
Which boulder has greater gravitational PE?
What other ways can an object store energy?

5. W = Fd B. Work Work transfer of energy through motion
force exerted through a distance
W = Fd
W: work (J)
F: force (N)
d: distance (m)
1 J = 1 N·m
Distance must be in direction of force!

6. B. Work
Brett’s backpack weighs 30 N. How much work is done on the backpack when he lifts it 1.5 m from the floor to his back?
GIVEN:
F = 30 N
d = 1.5 m
W = ?
WORK:
W = F·d
W = (30 N)(1.5 m)
W = 45 J F W d

7. d B. Work W F GIVEN: m = 40 kg d = 1.4 m - during d = 2.2 m - after
A dancer lifts a 40 kg ballerina 1.4 m in the air and walks forward 2.2 m. How much work is done on the ballerina during and after the lift?
GIVEN:
m = 40 kg
d = 1.4 m - during
d = 2.2 m - after
W = ?
WORK:
W = F·d F = m·a
F =(40kg)(9.8m/s2)=392 N
W = (392 N)(1.4 m)
W = 549 J during lift
No work after lift. “d” is not in the direction of the force. F W d

8. C. Conservation of Energy
Law of Conservation of Energy
Energy may change forms, but it cannot be created or destroyed under ordinary conditions.
EX:
PE  KE
mechanical  thermal
chemical  thermal

9. C. Conservation of Energy
PE  KE
View pendulum animation.
View roller coaster animation.

10. C. Conservation of Energy
Mechanical  Thermal
View rolling ball animations.
View skier animation.

11. II. Thermal Energy Temperature Thermal Energy Heat Transfer
Ch. 5 - Energy
II. Thermal Energy
Temperature
Thermal Energy
Heat Transfer

12. A. Temperature Temperature
measure of the average KE of the particles in a sample of matter

13. B. Thermal Energy Thermal Energy
the total energy of the particles in a material
KE - movement of particles
PE - forces within or between particles due to position
depends on temperature, mass, and type of substance

14. B. Thermal Energy A B Which beaker of water has more thermal energy?
B - same temperature, more mass
200 mL
80ºC A
400 mL B

15. C. Heat Transfer
Heat
thermal energy that flows from a warmer material to a cooler material
Like work, heat is...
measured in joules (J)
a transfer of energy

16. C. Heat Transfer A B Why does A feel hot and B feel cold?
Heat flows from A to your hand = hot.
Heat flows from your hand to B = cold.
80ºC A
10ºC B

17. C. Heat Transfer Specific Heat (Cp)
amount of energy required to raise the temp. of 1 kg of material by 1 degree Kelvin
units: J/(kg·K) or J/(kg·°C)

18. C. Heat Transfer Which sample will take longer to heat to 100°C?
50 g Al
50 g Cu
Al - It has a higher specific heat.
Al will also take longer to cool down.

19. Q = m  T  Cp C. Heat Transfer Q: heat (J) m: mass (kg)
T: change in temperature (K or °C)
Cp: specific heat (J/kg·K)
– Q = heat loss
+ Q = heat gain
T = Tf - Ti

20. C. Heat Transfer heat gained = heat lost Calorimeter
Coffee cup Calorimeter
Calorimeter
device used to measure changes in thermal energy
in an insulated system,
heat gained = heat lost

21. C. Heat Transfer GIVEN: WORK: m = 32 g Q = m·T·Cp Ti = 60°C
A 32-g silver spoon cools from 60°C to 20°C. How much heat is lost by the spoon?
GIVEN:
m = 32 g
Ti = 60°C
Tf = 20°C
Q = ?
Cp = 235 J/kg·K
WORK:
Q = m·T·Cp
m = 32 g = kg
T = 20°C - 60°C = – 40°C
Q = (0.032kg)(-40°C)(235J/kg·K)
Q = – 301 J

22. C. Heat Transfer GIVEN: WORK: m = 230 g Q = m·T·Cp Ti = 12°C
How much heat is required to warm 230 g of water from 12°C to 90°C?
GIVEN:
m = 230 g
Ti = 12°C
Tf = 90°C
Q = ?
Cp= 4184 J/kg·K
WORK:
Q = m·T·Cp
m = 230 g = 0.23 kg
T = 90°C - 12°C = 78°C
Q = (0.23kg)(78°C)(4184 J/kg·K)
Q = 75,061 J