PHYS 1111 - Introductory Physics Laboratory I
Laboratory
Advanced Sheet
Collisions
1. Objectives. The objectives of this laboratory are to confirm the conservation of linear momentum in elastic and perfectly inelastic collisions, and to investigate the change in kinetic energy in the same types of collisions.
2. Theory.
a. General. If no net external forces act in a collision, linear momentum is conserved, and
Kinetic energy is also conserved in elastic collisions,
Kinetic energy is not conserved in inelastic collisions due to work done by nonconservative forces,
b. Elastic collision. In a one-dimensional elastic collision between two masses, one of which is initially at rest, conservation of linear momentum leads to
If linear momentum is conserved,
Conservation of kinetic energy leads to
If kinetic energy is conserved,
b. Perfectly inelastic collision. In a one-dimensional, perfectly inelastic collision between two masses, one of which is initially at rest, conservation of linear momentum leads to
If linear momentum is conserved,
leading to
resulting in
3. Apparatus and experimental procedures.
a. Equipment.
1) Air track with blower.
2) Carts for air track.
3) Two photogates with computer interface.
4) Vernier calipers
5) Mass balance
b. Experimental setup. The experimental setup is shown in Figure 1 (to be provided by the student).
c. Capabilities. To be provided by the student.
d. Procedures. Detailed instructions are provided in paragraph 4b below.
4. Requirements.
a. In the laboratory.
1) Your instructor will introduce you to the equipment to be used in the experiment.
2) With the available equipment, design and execute an experiment to test conservation of linear momentum and kinetic energy in an elastic collision. Before conducting your experiment, discuss your plan with your instructor.
3) With the available equipment, design and execute an experiment to test conservation of linear momentum a perfectly inelastic collision and to compare predicted and measured final kinetic energies. Before conducting your experiment, discuss your plan with your instructor.
b. After the laboratory. The items listed on below will be turned in at the beginning of the next laboratory period. A complete laboratory report is not required for this laboratory. Use a spreadsheet program to make your calculations. Annex B provides a sample format for your calculations in the spreadsheet.
Para 3. Apparatus and experimental procedures.
1) Provide a figure for the experimental setup (para 3b).
2) Describe the capabilities of the equipment used in the experiment (para 3c).
Para. 4. Data.
1) Data from your measurements.
2) The following calculations:
a) Speeds, linear momenta and kinetic energies necessary to make your tests.
b) In the elastic collision, the value of Dp and DKE.
c) To assess the accuracy of the law of conservation of linear momentum, calculate the following:
d) To assess the accuracy of conservation of kinetic energy, calculate the following:
e) In the perfectly inelastic collision, calculate the value of Dp, and the predicted and measured values of KEf.
f) Use the formula in c) above to assess the accuracy of conservation of linear momentum.
g) Calculate the percent discrepancy between the measured and predicted values of KEf.
Para. 5. Results and Conclusions.
a. Results.
1) Provide a statement of the percent discrepancies in your results for the two conservation of linear momentum experiments.
2) Provide a statement of the percent discrepancies in your results for the two sets of kinetic energy measurements.
b. Conclusions.
1) Provide a statement of your conclusions on the validity of conservation of linear momentum in an elastic collision.
2) Provide a statement of your conclusions on the validity of conservation of kinetic energy in an elastic collision.
3) Provide a statement of your conclusions on the validity of conservation of linear momentum in a perfectly inelastic collision.
4) Provide a statement concerning the validity of the predicted value of the final kinetic energy of the combined masses in a perfectly inelastic collision.
5) Describe sources of random and systematic error in both of the experiments.
Annex A
Measurements
1 Elastic collision.
a. Masses of carts.
m1 = __________________ kg
m2 = __________________ kg
b. Lengths of carts.
L1 = __________________ m
L2 = __________________ m
c. Photogate times.
| trial | t1 (s) | t2 (s) | t3 (s) |
| 1 | |||
| 2 | |||
| 3 |
2. Perfectly inelastic collision.
a. Masses of carts.
m1 = __________________ kg
m2 = __________________ kg
b. Lengths of carts.
L1 = __________________ m
L2 = __________________ m
c. Photogate times.
trial |
t1 (s) |
t2 (s) |
1 |
||
2 |
||
3 |
Annex B
Calculations
1. Elastic collision.
a. Velocity calculations.
trial |
v1 |
v2 |
v3 |
1 |
|||
2 |
|||
3 |
b. Linear momentum calculations.
trial |
p1i |
p1f |
p2f |
pi,tot |
pf,tot |
Dp |
"% Disc" |
1 |
|||||||
2 |
|||||||
3 |
c. Kinetic energy calculations.
trial |
K1i (J) |
K1f (J) |
K2f (J) |
Ki,tot (J) |
Kf,tot (J) |
DK (J) |
"% Disc" |
1 |
|||||||
2 |
|||||||
3 |
2. Perfectly inelastic collision.
a. Velocity calculations.
trial
v1
(m/s)v2
(m/s)1
2
3
b. Linear momentum calculations.
trial
p1i
(kg m/s)pf
(kg m/s)Dp
(kg m/s)"% Disc"
1
2
3
c. Kinetic energy calculations.
trial
K1i (J)
Kf (J)
Kf,pred (J)
% Disc
1
2
3
Last update: July 02, 2007