1. CHAPTER 15 ENERGY
Section 15.1Energy and Its Forms

2. 15.1 Energy and Its Forms
• Underlying law of the universe “
The Law of Conservation of
Energy”
• Energy (nrg) is continuously converting
between many different forms.
• Energy is the ability to do work.
• Energy is transferred by a force. ( Work
and energy are closely related)

3. 15.1 Energy and Its Forms
• When work is done on an object energy is
transferred to the object.
• So work is a transfer of energy.
• Work and energy units are J ( Joules)
• What is food energy measured in?
Calories
• Different types of calories.
• Food Calories and heat calories.

4. 15.1 Energy and Its Forms
• A food Calorie is equal to 1kcal or 1000
conventional calories (heat calories)
• A conventional calorie = 4.184 J
• Can be converted to Joules. # of calories
in food. SI unit C for food calories, heat
calories c.
• Bodies goal is to burn off every calorie you
take in.

5. 15.1 Energy and Its Forms
• 2 General Types of Energy
• 1. Kinetic Energy - energy of motion
• It depends on its mass and speed.
• Formula:
• KE= 1/2 mv2
• KE Kineitic Energy = half mass times velocity
squared.
• KE = Joules
• Mass =kg
• Velocity Meters per second m/s

6. 15.1 Energy and Its Forms
• Book problem page 448
• Given
• M =0.10kg bird
• V=8.0 m/s
• What is the bird’s kinetic energy?
• Formula: KE= 1/2 mv2
• KE = ½ (0.10kg)(8.0m/s)2
• Solve either way
• KE=1/2 ( 0.10kg) (64m2/s2 ) or KE = 0.5 ( 0.10kg)
(64m2/s2 )
• =3.2 Kg × m2/s2
• =3.2 J

7. 15.1 Energy and Its Forms
• 2. Potential Energy (PE) – is energy that
is stored as a result of position or shape.
• It is basically energy with the potential to do
work.
• Ex. Holding a book, a rock on a cliff
• 2 forms of PE
• 1. Gravitational PE
• 2. Elastic PE

8. 15.1 Energy and Its Forms
• 1. Gravitational PE – potential energy that
depends on an objects height.
• It increases when a object is raised to a
higher level
• Calculating Gravitational PE
• Formula: PE = mgh
• Remember from chapter 12 Weight = mg
• m = mass and g= acceleration due to
gravity.

9. 15.1 Energy and Its Forms
• So often the formula for gravitational
potential energy is written using weight and
not with the mg.
• Potential energy general formula:
• PE = wt x ht Weight x height.
• PE units = Joules (J)
• Weight = Newtons (N)
• Height = meters (m)

10. 15.1 Energy and Its Forms
• Sample Problem 1(using PE = mgh) :
• A diver has a mass of 50.0 kg standing at
the top of a 10.0 m diving platform.
Calculate the PE relative to the ground.
• PE = mgh
• PE = (50.0 kg)(9.8 m/s2)(10.0 m)
• PE = 4900 kg• m2/s2
• PE = 4900 J

11. 15.1 Energy and Its Forms
• Sample Problem 2 (using PE = wt • ht):
• What is the potential energy of a 10 newton
book that is placed on a shelf that is 2.5
meters high?
• PE = wt • ht
• PE = (10 N)(2.5 m)
• PE = 25 N • m, remember a N • m is= to a J
• PE = 25 J

12. 15.1 Energy and Its Forms
• 2. Elastic PE- the potential energy of an
object that is stretched or compressed.
• An object is elastic if it springs back to its
original shape after it is stretched or
compressed.
• Ex: rubber band, slinky
• Elastic PE can be stored in objects that are
compressed like springs.
• Balls have compressed air in them.

13. 15.1 Energy and Its Forms
Know the forms of energy.
• Mechanical energy
• Thermal energy
• Chemical energy
• Electrical energy
• Electromagnetic energy
• Nuclear energy
• (make sure you write down each form in
your notes and give an example of each)