CONSERVATION OF MOMENTUM
p = mV. So the greater the mass, the greater the ________ . If 2 objects collide and if we neglect friction forces
the total momentum of the system is_________ . When an object is in motion and collide into another object at rest, it
will share its momentum with it. We will find out what role mass plays in determining the momentum of an object?
MATERIALS: track, marbles, steel balls,basket ball, ping pong ball
PROCEDURE
PART1: DRAW THE OUTCOMES
Make a track for the balls using the material given by your instructor (probably insulating pipes cut in half)see picture below. Use a book or a block under one end of the track to give a vertical height of about 2cm. Using tape, make sure the track does not move.
2) GEt 2 ball of the same mass (2 steel ball or 2 marbles)
Place one marble on the inclined track and one on the flat part. RElease the upper marble and, carefully observe the marbles prior to, and following the collision. What happened ?
Since both marbles have the same mass, momentum is __________ from one marble to the other.
3) Now place 1 marble on the incline and two marbles, touching, on the flat track. Release the upper marble and record the number of marble that move after the collision. Is this consistent with the conservation of momentum?
4) Same thing with 3 marbles at rest on the flat track. Record observations:
PART 2: collision 2 balls.
DRAW THE OUTCOMES
1) Place a small ball on the incline and a large ball on the flat part. Suppose the motion is initially @ right.
observe the velocities of balls before and immediately after collision.
velocity of the small ball is less than before collision ? more than before collision ? same or opposite direction (bouncing)?
velocity of the large sphere is small after collision? large ? direction is @ right or @ left ?
How is it consistent with conservation of momentum ? (think)
2) repeat but his time the large sphere is on the incline and the small one on the flat one. Observe velocities immediately after collision.
velocity of the large ball is less than before collision ? more than before collision ? same or opposite direction (bouncing)?
velocity of the small sphere is small after collision? large ? direction is @ right or @ left ?
How is it consistent with conservation of momentum ? (think)
3) both small spheres are on the flat part. They are a distance a part. Roll them toward each other at the same speed.
Observe velocities before and immediately after collision. Describe what happened and how it is consistent with the conservation of momentum.
(like you did for 1 and 2)
4) Roll a large and a small one toward each other. Record observations and explain in terms of momentum conservation.
(what happens to the magnitude of the velocities after collision compared to before ? what happens to the direction
of the velocities ? draw to show ).
PART3: crazy ping pong ball. You need a basket ball and a ping pong ball.
INTRODUCTION - Fill the blanks FOR FULL CREDITS
don't do the experiment. first do the computations.
First you should know how to compute relative speed. If a truck, moving at 30mph, is colliding with a
car at rest (0 speed), the relative speed is 30mph. But if both vehicles are moving at 30mph and then collide,
the damages are worse. This is because, the relative speed is now __________.
If 2 objects are moving toward each other, to find the relative speed, you need to ________ the speeds.
If a car and a truck are moving in the same direction, with the same speed (30mph) but a distance a part,
the relative speed is ___________. (that's why if 2 trains ride side to side, at about the same speed,
and if you sit in 1 train, the other train seems at rest, from your point of view.)
If a track is moving at 60mph followed by a truck moving at 30mph, their relative speed is ____________.
They move in the same direction, you need to ____________ the speeds to find the relative speed.
You are going to drop a ping pong ball on top on a basket ball. From a height of about d = 50cm = 0.5m.
Observe the picture below. If we neglect air resistance, the balls are falling at the same r ________, they are
in free-fall. Their acceleration is ______m/s/s. We can neglect air resistance because the basket ball is very ______
and it shields the ping pong ball from air resistance. The basketball bounces off the ground (without losing energy)
and collides with the ping pong ball. (1st image and 2nd image). At that point they both have about the same speed.
Then the ping pong collides with the basketball and bounces off.
The momentum is conserved and if energy is conserved (no energy loss after the basketball bounces the ground )
the relative speed of the balls before and after the collision is the same. This is true only for elastic
collision, when there is no energy loss.
Suppose the speed of the each ball before collision is 3m/s (remember they have the same speed, free fall)
Their relative speed before collision is therefore ____________ . (they move toward each other, add).
After collision the basket ball is still moving at 3m/s. (although it feels the same force, the change in speed is small for the
basketball because it has a large ___________.) After collision the balls are moving in the same direction
and their relative speed is still ___________. ( see what you got before).
Find the speed of the small speed if the relative speed is the same as before. (the number you just got)
(hint: they move in the same direction so relative speed = speed of small - speed of big, you have the speed of the big (3)
you have the relative speed (6) , you are solving for speed of the small).
speed of the small ball = ____________. Conclusion: the speed of the ping pong is ________ times greater
the speed it had before collision.
The speed is multiplied by ________ but the kinetic energy (energy of motion) is multiplied by ________ (square of speed)
So the ball will reach a height (if no air resistance) ________ times larger than the initial height.
NOW CHECK IF THIS IS TRUE. DO THE EXPERIMENT and
TRY TO EVALUATE THE RATIO BETWEEN INITIAL HEIGHT AND FINAL HEIGHT.
TRY if an egg instead of a ping pong !!! (let's go outside)
observations:
NOW TRY TO DROP THE PAIR (egg + basketball )FROM A LARGER HEIGHT. CLIMB STAIRS
observations