1. Energy, Temperature, & Heat
Chapters 13 and 14

2. Energy Energy is a measure of the ability to do work.
Whenever work is done, energy is transformed or is transferred from one system to another system.
Although work is done ONLY when an object experiences a change in its position or its motion, energy can be present in an object or system that is at rest.

3. Energy
SI Unit for energy: Joule (J)
There are two main categories of energy: NONMECHANICAL and MECHANICAL energy.

4. Types of Energy
Nonmechanical energy is small scale (meaning the scale of atoms).
Examples of NME include: thermal/heat, electromagnetic, nuclear, electric, sound, and chemical.

5. Nonmechanical energy Chemical Energy:
Energy associated with both the making and breaking of chemical bonds.
(ie. Batteries, food/digestion, photosynthesis) Lighting a match = chemical energy stored inside the head is released as light and heat.

6. Nonmechanical energy
Nuclear Energy:
Energy that binds the nucleus of an atom together. Can be released through nuclear fusion ( The Sun) or nuclear fission (nuclear power plants).

7. Nonmechanical energy
Electromagnetic:
Form of energy made from electrical and magnetic waves and packets of energy called photons. Can travel across empty space.
EM spectrum: Radio—Microwaves— Infrared—Visible Light—Ultra-Violet—X- ray—Gamma Rays

8. Nonmechanical energy Electrical Energy:
Energy associated with the flow of electrons through wires or other conducting materials.
When electrons move from an area of higher electric potential to an area of lower electric potential, they gain energy.
Appliances & Electronics

9. Nonmechanical energy
Sound Energy:
Energy that travels in waves by vibrating molecules in a medium.
Speed of sound (fastest to slowest)
Solids→→Liquids→→Gases

10. Nonmechanical energy
Thermal/Heat Energy:
Energy associated with the average kinetic energy of atoms or molecules.
Heat energy can be transferred in three ways:
Conduction
Convection
Radiation

11. Potential Kinetic Mechanical Energy
ME is large scale meaning you can SEE it.
Mechanical energy is composed of 2 types:
PE (potential energy) and KE (kinetic energy).
Potential
Kinetic

12. Potential Energy
Potential Energy is the stored energy resulting from the relative positions of objects in a system.
Called energy of position sometimes.
Two types of PE: Elastic & Gravitational

13. Potential Energy
Elastic Potential Energy: an object that is stretched or compressed to increase or decrease the distance between its parts.

14. Potential Energy
Gravitational Potential Energy depends on both the mass of the object and the height of the object relative to the Earth’s surface.

15. Kinetic Energy
Kinetic Energy is the energy of an object due to its motion.
2 things affect an object’s KE= mass of object and velocity object is traveling

16. Law of Conservation of Energy
The Law of Conservation of Energy says that ENERGY can not be created or destroyed, it can only change forms.

17. Law of Conservation of Energy
A perpetual motion machine is a machine designed to keep going forever without any input of energy.
This means ALL of the energy put into the machine stays in the machine perpetually (forever).
It’s a perfect model of the law of conservation except it’s
IMPOSSIBLE!!!!
Energy is constantly Changing forms!
Taccola’s Wheel

18. Law of Conservation of Energy
Potential energy can be transformed into kinetic energy and vice versa.
Example:
As a roller coaster is pulled up to the top of the first hill, the mechanical energy is stored as gravitational potential energy.
As it goes down the other side of the hill, the roller coaster picks up speed, transforming the potential energy to kinetic energy.
Roller Coaster Physics Design Your Own Roller Coaster

19. Heat and Temperature
Chapter 14

20. Temperature
Temperature is a measure of the average kinetic energy of all the particles within an object.
We measure temperature using a thermometer.

21. Temperature Thermometers work on a principle called thermal expansion.
As the temperature rises, the particles of a substance gain kinetic energy and move faster. With this increased motion, the particles of that substance move farther apart and expand the volume of a substance.

22. Temperature Scales
Around the world, three temperature scales are used: Fahrenheit (oF), Celsius (oC), Kelvin (K)

23. Temperature Scales
212
What is the freezing point and boiling point of water on the Fahrenheit scale? 32

24. Temperature Scales
100
What is the freezing point and boiling point of water on the Celsius scale?

25. Temperature Scales
The Kelvin scale is based on the principle of absolute zero.
Absolute zero is the coldest possible temperature, and it is also where an object’s energy is minimal.
Absolute zero is oC. The Kelvin scale was created so that absolute zero was in fact recorded as 0 kelvin or 0 K. (Kelvin has no negatives!)

26. Temperature Scales
373
What is the freezing point and boiling point of water on the Kelvin scale?
273

27. Temperature Conversions
How to convert from Celsius to Fahrenheit:
Fahrenheit temp. = (1.8 x Celsius temp.) +32.0
TF = 1.8 TC

28. Temperature Conversions
How to convert from Fahrenheit to Celsius:
Celsius temp. = (Fahrenheit temp )
1.8
TC = (TF )

29. Temperature Conversions
How to convert from Celsius to Kelvin and vice versa:
Celsius to Kelvin:
TK = TC + 273
Kelvin to Celsius:
TC = TK - 273

30. Temperature Conversions
If the boiling point of liquid hydrogen is oC, what is its boiling point in oF?
TF = 1.8 TC
TF = 1.8 ( )
TF = oF

31. Temperature Conversions
If the temperature of a winter day at the North Pole is oF, what is the temperature in oC?
TC = (TF ) / 1.8
TC = ( ) / 1.8
TC = oC

32. Temperature Conversions
The melting point of gold is 1064 oC, what is its melting point in K?
TK = TC + 273
TK =
TK = 1337 K

33. Temperature Conversions
The air temperature in a typical living room is 294 K, what is its temperature in oC?
TC = TK – 273
TC = 294 K – 273
TC = 21 oC

34. Temperature Conversions
The metal in a running car engine will typically get as hot as 388 K, how hot is this in oF?
TC = TK – 273
TC = 388 K – 273
TC = 115 oC
TF = TC
TF = (115 oC)
TF = 239 oF

35. Temperature Conversions
The air temperature on a summer day in the desert is typically 110 oF, what is the temperature in K?
TC = (TF ) / 1.8
TC = (110 oF ) / 1.8
TC = 43 oC
TK = TC + 273
TK = 43 oC + 273
TK = 316 K

36. Heat “Hot and “cold” has nothing to do with temperature.
“Cold” is felt when we lose energy to an object with less kinetic energy.
“Hot” is felt when we gain energy from an object with more kinetic energy.

37. Heat
Heat is the transfer of thermal energy from the particles of one object to those of another object due to a temperature difference between two objects.

38. Heat Transfer
The warmer object always transfers heat to the cooler object.
The greater the temperature difference, the faster the energy transfer.

39. Heat Transfer
Three methods of energy transfer are conduction, convection, and radiation.

40. Heat Transfer
Thermal conduction is the transfer of energy as heat between particles as they collide within a substance or between two objects in contact.

41. Heat Transfer
Convection is the transfer of energy by the movement of fluids with different temperatures.
A convection current is the flow of a fluid due to heated expansion followed by cooling and contraction.

42. Heat Transfer
Radiation is the transfer of energy by electromagnetic waves.
Radiation does not require contact.
It is the only method of energy transfer that can occur in a vacuum (outer space).

43. Conductors and Insulators
Conductors are a material through which energy can be easily transferred as heat.
Solids, especially metals like copper and silver, are the best conductors.

44. Conductors and Insulators
Insulators are a material that is a poor energy conductor.
Wood, rubber, fiberglass, Styrofoam, wool, etc.

45. Laws of Thermodynamics
First Law of Thermodynamics: the total energy used in any process is conserved, whether the energy is transferred as a result of work, heat, or both.

46. Laws of Thermodynamics
Second Law of Thermodynamics: the energy transferred as heat always moves from an object at a higher temperatures to an object at a lower temperature.

47. Specific Heat Capacity
Specific heat capacity is the amount of energy transferred as heat that will raise the temperature of 1 kg of a substance by 1 K.
Specific heat capacity is a physical property and will be the same any pure substance. Therefore, we can use it to identify substances.
Heat energy = specific heat capacity x mass x change of temp.
q = c x m x ΔT
(J)
(kg)
(K)
(J/kg * K)

48. Ch. 14 Section 2 Energy Transfer
A 10 g piece of iron absorbs 1000 joules of heat energy, and its temperature changes from 25°C to 100°C. Calculate the specific heat capacity of iron.
q =
ΔT=
c =
m =
1000 J
c = q / (m * ΔT)
c = 1000J/(10g*75oC)
= 75 oC q
c = 1000J/(750g*oC) ?
(c * m * ΔT)
c = 1.3 J/g*oC
10 g

49. Ch. 14 Section 2 Energy Transfer
To what temperature will a 20 g piece of glass raise if it absorbs 1000 joules of heat and its specific heat capacity is 0.50 J/g°C? The initial temperature of the glass is 10.0°C.
ΔT = q / (c * m)
ΔT = 1000J/(0.50 J/goC *20g)
q =
ΔT=
c =
m =
1000 J
ΔT = 1000/(10 oC)
Tf-10 = ? q
ΔT = 100 oC
0.50 J/goC
ΔT = Tf – To
(c * m * ΔT)
100oC = Tf – 10 oC
20 g
10oC+100oC=Tf –10oC+10oC
Tf = 110oC

50. Ch. 14 Section 2 Energy Transfer
100 g of 5.0°C water is heated until its temperature is 20°C. If the specific heat of water is 4.18 J/g°C, calculate the amount of heat energy needed to cause this rise in temperature.
q =
ΔT=
c =
m = ?
q = c * m * ΔT
q = 4.18 J/goC * 100 g * 15oC
15 oC q
q = 6,270 J
4.18 J/goC
(c * m * ΔT)
100 g

51. Answers to ODD Specific Heat Practice Problems
0.46 J/g0C 11) 0.21 J/g0C
3) 231 0C 13) 0.03 J/g0C
5) 13,794 J 15) 58,050 J
7) C 17) C
9) 79.7 g

52. Station 1: POP GOES THE POPCORN
1. What energy transformation occurs when the hot plate is turned on?
2. Record your observations as the popcorn kernels are heated up?
3. What type of heat transformation caused the kernels to pop?
4. Why don’t all the kernels pop at the same time?