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Chapter 4
Section 1
Energy
• Energy just like mass can neither be created nor
destroyed, it can only change form.
• Energy is the capacity of a system to do WORK.
• Energy exits in several forms such as:
– Heat (thermal)
– Mechanical
– Kinetic/Potential
– Light
– Electrical
– Chemical
Where does
the energy to
power this
player come
from?
Think of energy as money
• Money can exist in different forms: cash,
change, numbers in a bank account, silver,
gold…
• It takes energy (money) to perform different
acts. The energy is transferred around the
system .
• Ex: Coal
Energy
TV
Heat
Kinetic Energy
• This is the energy an object has in motion
because of its motion. It depends on an
objects mass and speed. It is measured in
Joules (J)
• KE (J)=1/2mass(kg) X speed(m/s)2
• KE=(0.5)mv2 or KE=⅟2mv2
• Kinetic energy will increase if:
____ Velocity increases
____ Mass increases
____ Height increases
KE Practice Problems
1. A jogger with a mass of 60 kg is moving at a
speed of 2 m/s. What is the jogger’s kinetic
energy?
2. A ball with a mass of 2 kg is moving at a speed of
3 m/s. What is the balls kinetic energy?
3. An object has a mass of 5 kg and a kinetic
energy 22.5 J. What is the object’s speed?
Potential Energy
• Energy stored within a motionless object
• There are 3 types of PE:
• Elastic PE—energy stored by something that
can stretch (spring or rubber band)
• Chemical PE—energy stored within chemical
bonds
Gravitational PE (GPE)
• The energy stored in anything that can fall.
• GPE (Joules) = mass (kg) x acceleration due to
gravity (9.8 m/s 2) x height (m)
• Acceleration due to gravity is a constant,
meaning the number will never change. It is
represented by a lower case g in physic
equations.
• GPE=mgh
GPE Practice Problems
1. What is the GPE of a book that has a mass of 1
kg and is sitting on a shelf 2 meters above the
ground?
2. How high above the ground is a ball with a mass
of 2 kg and a GPE of 70 J?
3. A rock climber 200 m above the ground has a
GPE of 10,000 J. What is the mass of the
climber?
• Can an object have kinetic energy and
potential energy at the same time?
• Two objects are sitting on the same table.
Object A has a mass of 3 kg and object B has a
mass of 5 kg. Which object has a higher GPE?
• How does speed and mass work together to
create KE?