Energy: Physics Concepts
Kinetic and Potential Energy
Part 1: Information
Key terms to know by the end of this session:
Kinetic energy
Gravitational
potential
energy
Elastic
potential
energy
Conservation
of energy
Work
Why do you need to know these concepts?
Concepts such as energy and work, together with the law of conservation of energy aid the understanding of
motion. There are many forms of energy; here we focus on kinetic and gravitation and elastic potential
energy.
What you need to know:
Types of Energy
Kinetic energy is energy of motion. The faster an object moves, the more kinetic energy it has.
Potential energy comes in various forms.
Gravitational potential energy is the energy an object has when at a height above the floor. As it
falls, it looses potential energy.
Elastic potential energy is energy stored in a spring or another flexible object. You know when you
release an object which is compressing a spring the object will shoot away from the spring. This is
the elastic potential energy changing to kinetic energy.
Conservation of energy
The Law states that energy is nether created or destroyed, it only changes form. This means that
when an ball is thrown in the air, it slows down (looses kinetic energy) as it gains height (gains
potential energy). Energy is transformed from kinetic to potential energy.
Work
Work, in a physics context, is a description of the amount of energy transformed in a process. For
example, the work done by gravity on a falling object is equal to the amount of energy transformed
from gravitational potential energy to kinetic energy. Work can be done in the direction of motion
(as in the previous example), but work can also be done opposite to the direction of motion.
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FORCES: Physics Concepts
Kinetic and Potential Energy
Part 2: Questions
Question 1:
Explain (in your own words) the difference between kinetic and potential energy
Question 2:
You throw a baseball straight up in the air, it moves vertically upwards, becomes stationary and then
falls back to your hand at the same height as it left it. Which of the following statements are true
(circle as many as apply).
(a) The kinetic energy is maximum at the top of the ball’s trajectory
(b) Ignoring air resistance, all of the kinetic energy you give the ball turns into potential energy
by the time the ball reaches its maximum height
(c) Potential energy increases, becomes zero at the top, then decreases as the ball falls
(d) According to conservation of energy the ball’s speed leaving you hand will be exactly the
same as the speed when it returns to your hand.
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FORCES: Physics Concepts
Kinetic and Potential Energy
Question 3:
Solve the following problem: For a roller coaster to make it
around a vertical loop (see diagram) it must be going at a
minimum speed based on the loop. If the loop is a circle with
radius 15m, how fast must the roller coaster car be going at the
bottom of the loop to make it around the whole loop?
Please explain your method in solving the problem as you go,
even if you are not sure how to solve it:
Image used with permission from freeimages.com
Part 3: Reflection
For each of the following questions, circle the response that best answers the question for you
Reflection 1:
How well do you think you know the concepts of Energy and Work?
Not at all
Not very
well
Average
Well
Very well
Reflection 2:
How helpful was this information for your study of physics this year?
Not at all
Not very
helpful
Partly
helpful
Page 3 of 3
Helpful
Very
helpful