LAB CONSERVATION OF MOMENTUM
PURPOSE:
To demonstrate the laws of conservation of momentum in elastic and
inelastic collisions.
Materials
1.
2.
3.
4.
5.
6.
aluminum ramp
steel balls
glass ball
wood ball drilled
plumb line and bob
C- clamp
7. meter stick
8. sheets of carbon paper (4)
9. sheets of paper
10. protractor
11. tape
Discussion:
In this experiment we will investigate what happens when two bodies collide and
move off in different directions. To do this we will use two steel balls of equal mass,
one of which will roll down an incline and make a glancing collision with the second
ball at rest on the support. As long as the air resistance can be neglected, objects
projected with different velocities will strike the ground at the same time. If either
ball has a vertical component of velocity this statement is no longer true. With this
in mind, it is essential that the target ball be positioned at the same
height as the ball leaving the end of the track.
The momentum of each ball can be determined from its mass and velocity. The
relative velocity of each ball can be found by measuring the distance from the point
on the floor directly below the target ball’s support post to the place where the ball
first strikes the floor. Multiplying the velocity by the mass gives the relative
momentum of that ball which can be drawn as a vector having the same direction as
the velocity. All momentum vectors must be drawn to the same scale and fit on the
assembled paper. It is useful to catch the ball on the first bounce to
avoid confusing records.
PROCEDURE:
Assembly: Use a C-clamp to fasten the flat plate of the launching ramp to the table top. The
flat base must extend over the edge of the table far enough to allow the plumb bob to reach
the paper on the foor.
Elastic collisions: SAME MASS
1. Place one of the ½” steel balls in the depression at the top of the set screw. This
will be the target support post. The set screw must be adjusted to the correct
height so that when the second ball is released and collides with the first steel ball
at an angle a single click is heard when the hit the floor. (Be sure the second ball
does not make contact with the set screw.
2. Construct a plumb line by tying one end of the thread to the bottom of the set
screw. Attach the other end of the thread to the eye of the screw and adjust the
height so that the tip of the screw is just a few millimeters above the floor.
3. Tape 4 pieces of paper together. (do not over lap the edges) Place the paper on the
floor so that the short end is just under the plumb line. Tape the paper to the
floor.
4. DATA COLLECTION (Record all info neatly on a separate sheet of paper)
a. Determine the height that the balls fall
b. Measure the mass of each ball
c. Set the ramp at an angle so that the second ball hits the first at an angle.
(Both balls must land on the paper) After you get your angle set be sure
not to bump the apparatus.
d. Lay the 4 sheets of carbon paper on top of your paper on the floor. Now
you are ready to gather your information on where the projectiles land.
e. Release the second ball from the same height and gather information for at
least 10 collisions at the same angle. Your results should look like the
picture below. (This info will give the momentum after the collision)
f. It is necessary to find the location where the ball strikes the floor when
there is no collision. With the set screw all the way down release the ball
from the top of the ramp at least 10 times to determine the location of
impact. ( This will give you the momentum before the collision)
According to the following diagrams you need to prove that momentum before the
collision is equal to the momentum after the collision. Remember momentum is a vector
quantity. The direction of the momentum is in the same direction as velocity.
Momentum = mass * velocity
Velocity = distance / time
Time =
2 * distance
9.8
SHOW MOMENTUM VECTORS ON THE DATA PAPER.
ELASTIC COLLISIONS: DIFFERENT MASSES
1. REPEAT ALL OF THE STEPS ABOVE USING TWO BALLS OF DIFFERENT
MASSES. Data may be recorded on the same 4 sheets of paper but be careful to
label all data according to the experiment performed.
INELASTIC COLLISIONS
In this experiment you will perform a perfectly inelastic collision in which the colliding
objects become on unit after the collision. You will use the same basic set up as the
previous collision experiments. The only difference will be the target. Place the hollow
ball on the screw at the end of the track. Adjust the set screw so that the center of the
hollow ball is in line with the center of the steel ball. Try a practice run. The steel ball
should stick inside the hollow ball. It can be assisted by putting a piece of masking tape
in the hole of the wooden ball. Adjust the height of the wooden ball as necessary. You
will need to prove the that momentum before the collision is equal to the momentum after
the collision. Be sure to record information for the momentum before the collision like
was done above.