Transcript Kinetic Energy

ACTIVITY #3: Passing Energy Along
As you walk into the Delaware State Fair,
you hear from a loudspeaker,
“Car #41 is speeding across the track and
…slams into car #56. Folks, I don’t know if either of
them is going to be able to continue!”
“What is going on?” you ask someone. The response … a
demolition derby!
A demolition derby is an event where contestants transform
ordinary cars into wrecking machines. The objective of the derby
is to be the last car running at the end of the event. So how do
you accomplish this task? You smash your car into the other cars
in the derby in an attempt to disable the other person’s car. A
good demolition derby driver knows where to hit another driver’s
car, how to hit the opponent’s car, and at the same time how to
protect
their own car from being destroyed. All of these
impacts deal with a transfer of energy.
•What happens to a car’s energy when it impacts another car?
•What affect does the speed of the car have on the severity of the
collision?
Where does the energy go after the collision?
In this investigation, you will roll a ball down the ramp (the ruler)
and allow it to roll into and collide with a Styrofoam cup that has
been cut in half. The cup and the ball slide along the tabletop until
they slow down and stop. It will not be as dramatic as two
demolition derby cars colliding, but the same energy principles will
apply for both examples.
GOALS: In this lab activity, you will …

Recognize that energy can be transferred from one
object to another. When this transfer of energy takes place,
the motion of both objects involved usually changes.

Recognize that there are other forms of energy besides
kinetic energy, and that energy can be easily transformed from
one form to another form.

Be introduced to process whereby the kinetic energy of
objects can be transferred to the tiny particles that make up
objects.
MAIN IDEAS: The important concepts and skills
covered in this activity are …

The kinetic energy of an object determines the amount of
change it can produce in the motion of other objects.

The kinetic energy of an object can be transferred to other
objects.

Objects can have stored energy that is called potential
energy. A common form of potential energy is due to the
Earth’s gravity. It is called the gravitational potential energy
and depends on the object’s mass and how high it is above the
ground.

Energy Transformation occurs whenever energy
changes from one form to another form.

The kinetic energy of objects can be transferred to the
tiny particles that make up the objects. When this happens, the
kinetic energy becomes disorganized and does not contribute
to the motion of the objects. Collectively, this random kinetic
energy is called heat energy.
Activity Overview: A synopsis of this lesson is as follows…
A ball is released from the top of a ramp. It rolls down the ramp
onto a horizontal surface. The ball rolls into a partial cup, and
pushes the cup a distance along the level surface that is
measured and recorded. The height of the ramp is then increased
and the exercise is repeated. As was the case in Activities #1 and
#2, students will need to take multiple measurements and
calculate average values throughout the experiment. Links are
made between how far the cup is pushed, how fast the ball was
moving at the bottom of the ramp, and the release height of the
ball. These observable quantities are used to describe the
transfer
ofwe
energy,
andthat
how
is transformed from one
In
Activity 1,
established
theenergy
higher the
ramp,to
theanother.
faster the ball. In Activity 2, the
form
kinetic energy of an object depends on its speed,
and mass. In this activity, the transfer of kinetic
energy from the ball to the cup and the
transformation of energy from one form to other
forms. Heat energy is one of these forms, and is
described using the Particle Model.
In summary, two important forms of energy are:
Kinetic Energy (KE), the energy an object has because of its
motion, which is determined by the object’s mass and speed.
Gravitational PE, the stored energy an object has because it was
lifted to some height. This potential energy is determined by the
object’s mass and its height above the ground.
Two important properties of energy are:
Energy transfer is the passing of energy from one object
to another.
Energy transformation is the changing of energy from
one form to another.
Let’s Investigate …
Part A – The Energy of a Solid Golf Ball
1.Gather the blocks and ruler needed to replicate the experimental
setup of the previous investigations. We will again use the
average speed results from the Let’s get the ball rolling activity
(Activity 1).
2.Gather a large Styrofoam cup and cut it in
half as shown in the diagram to the right.
3.Place the open end of the half cup at the bottom of the ramp so
that the ball enters the cup as soon as it leaves the ramp. The
ball will then travel a few centimeters before striking the back of
the cup and pushing it forward.
4.Release the solid ball from the top of the
ramp and record the distance that the cup
slides after impact
5.Repeat this task 4 more times at that height
and then calculate the average distance
traveled by the cup for this height. Record
your results in the data table.
6. Increase the height of the ramp by adding another
wooden block and then repeat steps 3, 4 and 5 of this
experiment.
7.After you have determined the average sliding distance for five
different ‘block’ heights, you are ready to prepare a graph. Plot
the distance traveled by the cup against the speed of the ball
(Note:
The speed of the ball for each ramp release height was determined and recorded
in Activity #1).
Question #1: Is the height of the ramp or the length of
the ramp more important in determining the speed the
ball when it reaches the bottom of the ramp? What
evidence do you have to support your claim?
8. Prepare a second graph. This time plot the distance the cup
travels against the height of the ramp.
Question #2: Using your graph, how far would you
predict
the cup would slide if you raised the height of
the ramp by one more block?
Question #3: Compare your two graphs. Where does
the golf ball have its greatest gravitational potential
energy? What evidence are you using to support your
decision
REMEMBER:
Gravitational PE, the stored energy an object has because it
was lifted to some height.
Part B - The Energy of a Hollow Golf Ball
Repeat Steps 3-6 in Part A, this time using a hollow golf ball, and answer
the following question in your journal or notebook.
Question #4: For the same ramp height, which has more
gravitational potential energy, the solid golf ball or the hollow
golf ball? What evidence is there to support your decision?”
Part C – Where Did the Energy Go?
Talk to your lab partners and describe what happens to the
energy that you gave the golf ball when you lifted it to the top
of the ramp. Trace what became of this energy as the ball
was placed on the ramp, released and finally rolled to rest with
the cup.
Record your discussion
Draw an energy chain
In this event the energy given to the ball was delivered to the ball
by the student lifting the ball. Without providing any details, we
state that this energy comes from the food eaten by the student.
The students muscles transfer this ‘food energy’ to the ball where
it is transformed into stored gravitational potential energy. When
the ball was released, this stored energy was transformed into the
energy of motion, kinetic energy. The
ball transfers its
kinetic energy
to the cup, and
they both
slide to rest.
Law of the Conservation of
Energy
Summary of Activity …
In your journal or notebook, write a concise summary of this activity.
Be sure to address the following questions and use your data to support
your responses.
1.What are the differences between the energy of motion (kinetic energy),
stored energy (potential energy) and how does energy transformation
connect these two energy forms?
2.How is energy transfer different from energy transformation, and what
examples are there of energy transfer in this activity?
3.What are the differences between the kinetic energy of an object and
the random kinetic energy of the particles that make up the object (heat
energy)?
Applying what you have learned …
1. A stream of water starts high in the foothills,
flows down through the hills and into the flatlands
at the base of the foothills. If the same water
made the trip
from the top of the foothills through a large
smooth pipe, it would be moving much faster
when it reached the flatlands than the stream
water
does.
Use
the
concepts
of
energy
•
transformation and energy transfer to explain how
the water in a stream can move downhill without
speeding up.
Investigating Further …
Friction is a force that can be helpful in some cases or not so helpful in other
situations. In this activity, we saw that friction was a significant force in the
transformation of energy process. It was the force responsible for transforming
the kinetic energy of the cup to thermal energy of the surface and surroundings.
But what is friction?
A true understanding of friction is not yet known, but scientists who study
friction (called tribologists) can describe how it operates. Friction is a force that
always tries to prevent two surfaces from slipping past one another. If the
object is already slipping (we call this sliding) friction will act prevent it.
Suppose there is a 50 pound box sitting on the floor. You push on it just a little
and realize that it is going to take much more than just a small push to get it
moving. What is keeping it stationary? The force of friction between the bottom
of the box and the floor attempts to counteract your pushing to prevent slipping.
Likewise, if you are pushing a box across the floor and then let go, it will slide to
a stop. It is the force of friction that has stopped the box.
Friction primarily depends upon two factors. The first factor is simply
how rough or smooth the actual surfaces are. The second factor is how hard
the two surfaces are pushed together. On level surfaces the weight of the
object is equal to how hard the two surfaces are pushed together, so scientists
sometimes say that the amount of friction is dependent upon the weight of the
--Gymnasts use a rosin dust to improve grip on some equipment.
--Violinists rosin their bows to increase the ‘grabbing effect’
produced by friction on the violin strings.
--Some ballpoint pens have numerous tiny dents in the tip to
prevent ink from acting like a lubricant.
--A human arm and socket have as little friction as a lubricated
ball bearing
What type of energy do you see?