Download Conservation of Energy_Pendulum Lab

Conservation of Energy Lab: The Pendulum
Introduction:
The work done to elevate the pendulum to its initial height (force times the distance)
becomes stored as potential energy with respect to the bottom of the swing. At the top of
the swing, all the energy of the pendulum is in the form of potential energy. At the bottom
of the swing, all the energy of the pendulum is in the form of kinetic energy.
The total energy of a system is the sum (Σ) of its kinetic and potential energies. If energy
is conserved, the sum of the kinetic energy and potential energy at one moment will equal
their sum at any other moment. For a pendulum, the kinetic energy is zero at the top, and
the potential energy is zero at the bottom. Thus, if the energy of a pendulum is
conserved, the potential energy at the top must equal the kinetic energy at the bottom. In
this experiment, you will measure kinetic and potential energy and see if their sum is
conserved.
!Materials:
(1)
(1)
(1)
(1)
(1)
(1)
!
!
Ring stand
Timer
Piece of string
Meter stick
Pendulum bob
Digital balance
Possible Equations
Needed:
W = Fd
PE = mgh
KE = 1/2mv2
ΣPE = ΣKE
!
Symbols:
W: Work (W)
PE: Potential Energy (J)
KE: Kinetic Energy (J)
m: mass (kg)
g: acceleration due to gravity
(m/s2)
h: height (m)
v: velocity (m/s)
Σ: sum/total
Procedures:
1. Attach a pendulum clamp to the top of a ring stand.
2. Find the mass (g) of the pendulum bob using the digital scale at the front of the room.
3. Convert the mass from grams (g) to kilograms (kg). Record mass in your notebook.
4. Cut a length of string and attach the pendulum bob to a piece of string. BE SURE the
string is not so long that when it swings it hits the ground. Record the string’s length
in meters (m) in your notebook.
5. Attach the string with bob to the pendulum clamp on the ring stand.
6. Predict what height the ball will reach when the ball is released from a perpendicular
(90o) position relative to the ring stand. Record your prediction in your notebook.
a. The ball will go higher than the release height.
b. The ball will go just as high as the release height.
c. The ball will not go as high as the release height.
7. Release the pendulum bob. Record, in your notebook, whether you observe situation
a,b, or c.
Conservation of Energy Lab: The Pendulum
8. Calculate the work done (W) in joules (J) to raise the pendulum bob to its release
position (a.k.a. release height). Record in your notebook.
9. Calculate the potential energy (PE) in joules (J) of the pendulum bob at its release
position. Record in your notebook.
10.Calculate the kinetic energy (KE) in joules (J) of the pendulum bob at the lowest
position of its swing.
NOTE: When calculating the velocity of the pendulum bob use the release height
minus the height of the lowest position of its swing as the distance it traveled.
!
Application Questions
Please write responses in COMPLETE SENTENCES. Fully explain your thinking as if I have
no idea what you have done in this lab and I need you to explain all the details to me.
1. Include a diagram of your pendulum set-up and label it with all the components (ring
stand, string, bob, etc.) and quantities, such as the height from which the bob is
released, string length, potential energy, kinetic energy, work done, velocity, etc.
2. Explain, using your results, why the work done on and the potential energy of the
pendulum bob are the same amount of joules (J).
3. Describe what happens to the potential energy (PE) and the kinetic energy (KE) of the
pendulum bob as it swings from the release position (a.k.a. release height) to the
lowest position.
4. Describe what happens to the total energy (ΣE) of the pendulum bob as it swings from
the release position through the lowest position to the top of its swing and back to its
release position (a.k.a. the entire journey).
5. Calculate the percent of energy that is conserved using the following equation:
% Energy Difference = PE - KE x 100
PE
Based on your calculations, does the total energy of the pendulum bob remain the
same throughout the swing? If not, what caused the difference?
6. Explain how you could increase the potential, and thereby, the kinetic energy of the
pendulum bob.
!
!
!
!
!
!
!
!
!
!
!
!
!
!
The gold star is placed next to the section that will be turned in for grading.