1. Chapter 13: Work and Energy
Section 3: What is energy?

2. Energy and work
Whenever work is done, energy is transformed or is transferred from one system to another system
Definition of energy: The ability to do work
Energy comes in many forms:
Nuclear
Chemical
Mechanical
Heat
Sound
Energy is measured in Joules (J)… just like work!
The ones we are talking about in physical science.

3. Types of Mechanical Energy
POTENTIAL ENERGY
Kinetic energy
The energy that an object has because of the position, shape, or condition of the object.
Two types:
Elastic potential energy
Gravitational potential energy
The energy that an object has due to the object’s motion
𝐾𝐸= 1 2 𝑚 𝑣 2
𝑃𝐸 𝑔 =𝑚𝑔ℎ
Total mechanical energy = PE + KE

4. More about Potential Energy
Sometimes this type of energy is referred to as Stored energy
Elastic potential energy depends on how stretched or compressed the object is
Gravitational potential energy depends on
The mass of the object
The relative height
Relative to where the reference point is defined

5. More about kinetic energy
Kinetic energy depends on
The mass of the object
How fast the object is moving
Because velocity is squared, KE depends on speed more than mass
Atoms and molecules have kinetic energy, because they are always moving.

6. Other forms of energy Chemical reactions involve potential energy
Photosynthesis is the process that turns energy from the sun into chemical energy that is stored in sugars and other molecules in cells
When you eat, you are eating stored energy… potential energy
The sun gets energy from nuclear reactions, called nuclear fusion
Energy can be stored in fields
Earth’s gravitational field stores gravitational potential energy
Electric fields store electrical energy