1. Energy Chapter 5

2. Energy is the ability to do work or cause change
What is Energy 5.1
Energy is the ability to do work or cause change
Work is done when a force moves an object through a distance.
W = F x D

3. Work and Energy
When an object or living thing does work on another object, some of its energy is transferred to that object
Therefore: Work can be thought of as the transfer of energy.
When energy is transferred, the object upon which the work is done gains energy.
Energy is measured in Joules (same unit as work)

4. Power and Energy Power is the rate at which work is done
If the transfer of energy is work, then power is the rate at which energy is transferred OR the amount of energy transferred in one unit of time
Power = Energy transferred
Time

5. Power & Energy Power is involved whenever energy is being transferred.
Calm breeze vs. Tornado
Power of both is the rate of energy transfer to lift a leaf a certain distance
Tornado has the same energy transfer, but with more power because it transfers the energy at a quicker rate.

6. Types of Energy Two basic types of energy Kinetic Potential
Type of energy depends on if the object is moving or not.
A moving object can do work when it strikes another object and moves it some distance
The energy an object has due to its motion is called kinetic energy
Greek word kinetos = moving

7. Factors affecting Kinetic Energy (KE)
Kinetic energy depends on
Mass
Velocity
KE increases as mass increases
KE increases as velocity increases

8. Calculating KE KE = ½ x mass x velocity 2
Does changing the mass and velocity have the same affect on KE?
NO – changing the velocity has a greater effect on KE than changing the mass by the same factor.
WHY? – because velocity is squared.
Therefore, doubling the mass will double the KE, but doubling the velocity will quadruple the KE.

9. Potential Energy (PE)
An object does not have to be moving to have energy
Some objects have stored energy
Result of their shapes or positions
Lift a book off the floor to your desk
Compress a spring to wind a toy.
Energy has been transferred to those objects in both examples and is stored.
May be used later when the book falls to the floor or the spring unwinds.
Stored energy as a result of shape or position of an object is potential energy.
This type of energy has the “potential” to do work.

10. Gravitational Potential Energy (GPE)
Defined as potential energy related to an objects height.
GPE equaled to the work done to lift the object
Recall: work = force x distance
The force used to lift the object equals the weight of the object
The distance the object is moved is the object’s height

11. Gravitational Potential Energy (GPE)
Formula to calculate GPE
GPE = mass x gravity x height
Simplified as GPE = weight x height
REMEMBER: weight = mass x force of gravity
Gravity On Earth = 9.8 m/s2

12. Example:

13. Calculate
If the ski jump is 40m high, what is the GPE of the
Green skier = 600N
Red Skier = 500N
500 Newtons x 40m = 20,000 J GPE
600 Newtons x 40m = 24,000 J GPE

14. Elastic Potential Energy (EPE)
An object gains a different type of potential energy when it is stretched
Elastic potential energy – the potential energy associated with objects that can be stretched or compressed

15. Formula to calculate Elastic potential energy
EPE = ½ kx2

16. Chapter 5-2 Forms of Energy
Energy comes in many forms
Mechanical energy – associated with the position and motion of an object
A combination of potential and kinetic
Calculation:
Mechanical Energy = Kinetic energy + Potential Energy

17. Example of ME calculation
A football thrown by a quarterback has BOTH PE and KE. The higher the ball is thrown the greater the PE, the faster it is thrown the greater the KE.
PE = 32J
KE = 45 J
Mechanical Energy (ME) = 77J (32+45)
An object with mechanical energy can do work on another object
Mechanical energy is the ability to do work.
The more ME an object has the more work it can do.

18. Other forms of energy
These other forms are associated with the particles that make up objects.
These particles are too small to be seen. (atoms & molecules)
Thermal energy
Electrical energy
Chemical energy
Nuclear energy
Electromagnetic energy

19. Thermal energy
All objects are made up of atoms and molecules
Atoms and molecules are in constant motion – therefore they have kinetic energy
Atoms and molecules are arranged differently in different objects – therefore they have potential energy

20. Thermal Energy
Total PE and KE of particles in a substance = thermal energy
Example Melting ice cream
Fast moving particles in warm air, make the particles in the ice cream move faster, as the kinetic energy of the ice cream particles increases, the thermal energy increases. The ice cream melts.

21. The energy of electric charges
Electrical energy
The energy of electric charges
Depending on whether the charges are stored or moving, EE can be kinetic or potential.

22. Almost everything is made up of chemical compounds
Chemical Energy
Almost everything is made up of chemical compounds
Chemical compounds are made up of atoms and molecules
Bonds between the atoms and molecules hold the compounds together
These chemical bonds have energy

23. Chemical Energy
CE is the energy stored within the chemical bonds of substances.
Food we eat
Matches
Cells in our body
When bonds break, chemical energy is released and new compounds may form

24. Nuclear Energy A type of potential energy
Stored in the nucleus of an atom
Released during a nuclear reaction
Nuclear fission – occurs when a nucleus of an atom is split
Used in nuclear power plants

25. Nuclear Energy
Nuclear fusion – occurs when the nuclei of atoms join together
Occur continuously in the sun, release tremendous amounts of energy

26. Electromagnetic Energy
Sunlight is a form of Electromagnetic energy
Travels in waves
EM waves have both electrical and magnetic properties
Examples
Microwaves
X-rays
UV radiation
Infrared radiation
Radio waves

27. 5.3 Energy Transformation and Conservation
Niagara Falls
A center for a network of electrical power lines
Water above the falls is used to generate electricity.

28. Energy Transformations
The mechanical energy of moving water can be transformed into electrical energy.
Most forms of energy can be transformed into other forms of energy.
A change from one for of energy to another is called: energy transformation

29. Single Transformations

30. Multiple Transformations
Often a series of transformations are needed to do work
A match
Mechanical - Thermal - Chemical - Thermal - Electromagnetic
The ME used to strike the match is transformed into TE. TE causes the particles in the match to release stored chemical energy, which is transformed into TE and the EME seen as light.

31. Multiple Transformations
A car engine
EE produces a spark- TE of spark -> releases CE in fuel - CE turns into TE - TE converted into ME & EE

32. Transformations between Potential and Kinetic Energy
Transformation between Potential energy and Kinetic energy is the most common form of transformation.
Any object that rises and falls experiences a change in its kinetic and gravitational potential energy.

33. Energy transformation in juggling
No motion at its highest point, no KE, maximum PE
Decreasing KE as it rises
PE decreasing, Rising KE
In motion = KE
High KE
No motion = no KE, ball has PE

34. Energy transformation in a pendulum
Pendulum continuously transforms energy from kinetic to potential and back.

35. Conservation of Energy
The law of conservation of energy states:
When one form of energy is transformed to another, no energy is destroyed in the process. Energy cannot be created or destroyed
The total amount energy is the same before and after any transformation. If you add up all the new forms of energy after a transformation, all the original energy will be accounted for.

36. Energy and friction
Scenario: If you set a spinning top in motion, will it stay in motion forever?
WHY?
As the top spins, in encounters friction with the surface it is spinning on and with the air.
Whenever a moving object experiences friction, some of the KE is transformed into TE.
The fact that friction transforms mechanical energy into thermal energy explains why no machine is 100% efficient.
Output work is always less than input work in a real machine.

37. Energy and matter Albert Einstein’s Theory of Relativity
During some nuclear reactions, matter is converted to energy.
Einstein showed that energy and mass are equivalent and can be converted into one another.
E = mc2 is the equation to calculate the amount of energy that is created when matter is destroyed.
Matter = anything that has mass and takes up space

38. 5.4 Energy and Fossil Fuels
Earth 400 million years ago
Lush green swampy forest
Enormous dragon flies
Huge cockroaches

39. Formation of Fossil Fuels
Fuel – a material that contains stored potential energy
Ex. Gasoline used in cars, propane used in grills
Fuels used today were formed hundreds of million of years ago.
These fuels include:
Coal, petroleum, and natural gas
Known as Fossil Fuels

40. Formation of Fossil Fuels
Vast ancient forests were the source of coal
When plants and animals died, their remains piled up in thick layers in swamps and marshes
Clay and sediment covered their remain
Over time, increased pressure and temperature turned their remains into coal

41. Meaning: fuels do not create energy Fossil fuels store energy
Energy from the sun
Energy is conserved
Meaning: fuels do not create energy
Fossil fuels store energy
Where did they get the energy from?
The sun

42. Energy from the sun Fossil fuels contain energy that came from the sun
The sun is the source of energy for most of Earth’s processes
Within the dense core of the sun – the process of nuclear fusion –> nuclear energy is transformed into electromagnetic energy as well as other forms.
Some of this electromagnetic energy reaches the Earth as light.

43. The Sun’s energy on Earth
When the sun’s energy reaches earth
Plants, algae, and certain bacteria - transform some of the light into chemical energy
Some of the energy in the chemical compounds they make is used for their daily needs. The rest is stored.

44. The Sun’s energy on Earth
Animals eat plants – store some of the plants chemical energy in their cells
When the animals and plants died – some of the energy stored is trapped within them
This trapped energy is the chemical energy found in coal.

45. Burning fuels is known as combustion
Use of Fossil Fuels
Fossil Fuels can be burned to release the chemical energy stored millions of years ago.
Burning fuels is known as combustion
During combustion, chemical energy is transformed to thermal energy
Thermal energy can heat water to produce steam.

46. Ex. Modern coal fired power plants:
Steam is raised to a high temp in a boiler – leaves the boiler with high pressure – turns a turbine
A turbine is a fan connected to an axle – steam causes the blades of the fan to turn very fast – thermal energy is converted to mechanical energy.
Turbines are connected to generators that produce electricity.
Chemical –> thermal –> mechanical -> electrical

47. Coal-fired power plants