Download Getting to Know: Kinetic Energy

Getting to Know: Kinetic Energy
The motion of a rollercoaster thrills riders as they fly
down hills, twist around corners, and even wind up
topsy-turvy as they pass through loops of track. You
may have noticed that rollercoaster cars are pulled
up the first hill by a motor and chain, but once they
reach the top, the cars roll through the remainder
of the ride without any help from outside forces. It’s
easy to imagine that gravity pulls the cars down the
hill, but how do they get up the next hill or through
the loops? The answer is in the energy of the cars as
they roll through the ride.
What is energy?
People use the words “energy” and “work” in a
lot of different ways, but in science, energy is the
ability to do work and work is moving a mass over
a distance. Energy comes in many forms and can
change from one form to another. Kinetic energy
is the energy that a moving object has as a result
of its mass and its motion. The kinetic energy of
an object is equal to one-half of its mass times the
square of its velocity. Velocity is a measurement
that accounts for both speed and direction. The
A rollercoaster works because energy
rollercoaster cars have kinetic energy as they move
continually changes form between potential
and kinetic energy.
along the track. The cars also have potential energy,
which is stored energy that can be released to
do work. Potential energy increases with height above Earth’s surface because the force of
gravity will move an object downward once the object is released from its position. During
the ride, the energy of the rollercoaster cars continually changes between potential and
kinetic.
Misconception 1: Isn’t energy the same thing as force?
No, energy and force are two different things. A force is a push or a pull. For example,
a chain exerts force on the rollercoaster cars when it pulls them up to the top of the
first hill. The force of gravity pulls the rollercoaster cars down the tracks. However, the
rollercoaster cars have energy—the ability to do work. In this case, the work is moving
the mass of the cars and the riders over the distance of the track.
Concept: Kinetic Energy
Getting to Know
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How does energy change forms?
On the rollercoaster ride, energy changes forms between potential and kinetic every time the
cars move up or down. At the top of the first hill, the cars have a lot of potential energy. As
the cars move down the hill, some of that potential energy changes to kinetic energy. A car’s
kinetic energy carries it up the next hill, and kinetic energy changes to potential energy as
the car moves upward. As a car crests the hill and starts moving downward again, some of its
potential energy changes back to kinetic energy. These changes continue throughout the ride.
Misconception 2: Some energy is destroyed as it changes from one form to another.
That’s why the rollercoaster slows on each hill and eventually comes to a stop.
Actually, energy can never be created or destroyed; it can only change form. The
rollercoaster cars slow as they lose kinetic energy, but that kinetic energy isn’t destroyed;
it simply changes to another form of energy.
The rollercoaster slows as some of its kinetic energy changes to heat energy as a result
of friction. Friction is the force caused by objects rubbing together. Friction causes
objects that rub together to heat up.
Can kinetic energy transfer from one
object to another?
It can! Remember that energy is the ability to do
work or to move a mass over a distance. When
one moving object comes into contact with
another object, it applies a force that can move
that object. When the second object moves, it
gains kinetic energy from the first object—energy
transfer has occurred.
Think about hitting a ball with a bat. The swinging
bat has kinetic energy. When the bat hits the
ball, it applies force that moves the ball in the
direction of the swing. Some of the bat’s kinetic
energy has transferred to the ball.
Now that you know a little more about kinetic energy, let’s get started with our lesson!
When the batter hits the ball, the kinetic
energy of the swinging bat transfers to the
ball and the ball flies through the air.
Concept: Kinetic Energy
Getting to Know
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© Discovery Education. All rights reserved.
Discovery Education is a subsidiary
of Discovery Communications, LLC.