Chemists divide energy into two classes. Kinetic energy is energy possessed by an object in motion. The earth revolving around the sun, you walking down the street, and molecules moving in space all have kinetic energy. Kinetic energy is directly proportional to the mass of the object and to the square of its velocity: K.E. = 1/2 m v2. If the mass has units of kilograms and the velocity of meters per second, the kinetic energy has units of kilograms-meters squared per second squared. Kinetic energy is usually measured in units of Joules (J); one Joule is equal to 1 kg m2 / s2.

1. Unit 2 Lesson 2 Kinetic and Potential Energy
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2. On the Move
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What is kinetic energy?
• Energy is the ability to cause change. There are
different forms of energy. One form is kinetic
energy, the energy of motion.
• Every moving object has kinetic energy. The
faster an object moves, the more kinetic energy it
has. If two objects move at the same speed, the
object that has more mass will have more kinetic
energy.
Unit 2 Lesson 2 Kinetic and Potential Energy

3. How is the kinetic energy of an object
calculated?
• The kinetic energy of an object equals one-half
the object’s mass (m) times the square of its
volume (v).
• Kinetic energy = mv2
• When mass is expressed in kilograms (kg) and
speed in meters per second (m/s), kinetic energy
is expressed in joules (J).
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Unit 2 Lesson 2 Kinetic and Potential Energy
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4. It Could Change
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What determines the potential energy
of an object?
• An object that is not moving can still have energy.
Potential energy is the energy an object has
because of its position, condition, or chemical
composition.
• An object has elastic potential energy when it has
been stretched or compressed. Elastic potential
energy is stored in a stretched spring or a rubber
band.
Unit 2 Lesson 2 Kinetic and Potential Energy

5. What determines the potential energy
of an object?
• An object has gravitational potential energy due to
its position above the ground. An object held
above the ground has the potential to fall. The
higher the object is above the ground, the greater
its gravitational potential energy.
• Potential energy that depends on an object’s
position is referred to as mechanical potential
energy.
• A substance stores chemical potential energy as a
result of its chemical bonds. Some of that energy
can be released during chemical reactions.
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Unit 2 Lesson 2 Kinetic and Potential Energy

6. How is the gravitational potential
energy of an object calculated?
• The gravitational potential energy of an object
equals its mass (m) times its height above the
ground (h) times the acceleration due to Earth’s
gravity (g).
• Gravitational potential energy = mgh
• An object’s mass is expressed in kilograms. An
object’s height above the ground is expressed in
meters. The acceleration due to Earth’s gravity is
9.8 m/s2
.
• Potential energy is expressed in units of joules.
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Unit 2 Lesson 2 Kinetic and Potential Energy

7. How is the gravitational potential
energy of an object calculated?
• When does the bouncing ball have zero
gravitational potential energy?
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Unit 2 Lesson 2 Kinetic and Potential Energy

8. It All Adds Up!
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How is the mechanical energy of an
object calculated?
• A moving object can have both kinetic and
potential energy. Mechanical energy is the
energy possessed by an object due to its motion
and position.
• The sum of an object’s kinetic energy (KE) and
mechanical potential energy (PE) is its mechanical
energy (ME).
• ME = KE + PE
Unit 2 Lesson 2 Kinetic and Potential Energy

9. How is the mechanical energy of an
object calculated?
• If the object’s only potential energy is
gravitational potential energy, you can use the
following equation to find mechanical energy.
• ME = mv2
+ mgh
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Unit 2 Lesson 2 Kinetic and Potential Energy
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10. How is the mechanical energy of an
object calculated?
• As the basketball falls to the ground, its kinetic
energy increases and its gravitational potential
energy decreases. However, its mechanical energy
remains constant.
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Unit 2 Lesson 2 Kinetic and Potential Energy