1. The Nature of Energy
Chapter 4

2. What is energy?
Energy is the ability to cause a change.

3. Kinetic Energy Kinetic energy – energy in the form of motion
The amount of kinetic energy an object has depends on its mass and its speed

4. Kinetic Energy Kinetic energy – energy in the form of motion
The amount of kinetic energy an object has depends on its mass and its speed
Kinetic energy = ½ mass X speed2

5. Kinetic Energy Kinetic energy – energy in the form of motion
The amount of kinetic energy an object has depends on its mass and its speed
Kinetic energy = ½ mass X speed2
Joule – the SI unit used to measure energy

6. Potential Energy
Potential Energy – energy stored in a motionless object, giving it the potential to cause change

7. Elastic Potential Energy
Energy stored by things that stretch or compress

8. Chemical Potential Energy
Energy stored in chemical bonds between atoms
Example: Food you eat or Gasoline for your car

9. Gravitational Potential Energy
Energy stored by things that are above the earth

10. Gravitational Potential Energy
Energy stored by things that are above the earth
The amount of GPE an object has depends on its mass, the acceleration due to gravity, and its height above the ground
GPE = mass in kilograms X 9.8 m/s2 X height in meters

11. Gravitational Potential Energy
GPE = mass X gravity X height
Mass in kilograms
Gravity in m/s2
height in meters
GPE = mgh

12. Chapter 4
Section 2

13. Conservation of Energy

14. Conservation of Energy
Energy Conservation – energy changing from one form to another

15. Conservation of Energy
Energy Conservation– energy changing from one form to another
Fuels store energy in the form of chemical potential energy

16. Conservation of Energy
Energy Coservation – energy changing from one form to another
Fuels store energy in the form of chemical potential energy
Mechanical Energy – the total amount of potential and kinetic energy in a system
ME = PE + KE

17. Law of Conservation of Energy
Law of conservation of Energy – energy may change from one form to another, but the total amount of energy never changes
Example – as a swing moves back and forth, its energy continually converts from kinetic to potential energy and back

18. Law of Conservation of Energy
Law of conservation of Energy – energy may change from one form to another, but the total amount of energy never changes
Example – as a swing moves back and forth, its energy continually converts from kinetic to potential energy and back
If the energy of the swing decreases, then the energy of some other object must increase by an equal amount
Friction converts some of the mechanical energy into thermal energy

19. Converting mass into energy…

20. Converting mass into energy…
Nuclear energy – you must think of mass as energy when discussing nuclear reactions. The total amount of mass and energy is conserved
Nuclear fusion – two nuclei are fused together – takes place in the sun
Nuclear fission – nuclei is broke apart

21. Conservation of Energy… In your body???
Stored chemical PE changes to KE… keeps your body at a certain temp (thermal energy)
Chemical potential energy from food that is stored in your body is used to fuel the processes that keep you alive

22. Calories Used in 1 hour of…
Type of Activity
Small body frame
Medium Body Frame
Large body frame
Sleeping 48 56 64
Sitting 72 84 96
Eating 98
112
Standing
123
Walking
180
210
240
Playing Tennis
380
420
460
Bicycling (fast)
500
600
700
Running
850
1,000

23. What is a calorie?
A food calorie is used to measure how much energy you get from various foods.
Food energy is measured in joules in the SI system. The standard energy unit used by nutritionists in the United States is the Calorie. One Calorie (with a capital “C”) is also known as a kilocalorie and is equal to 1000 calories (lower case “c”). One calorie is equal to joules.
calorie = joules
Calorie = 4,184 joules