heavy rod base
long steel rod
rotary motion sensor
2 photogates with cords
projectile loading ramrod
safety glasses (one pair per person)
weigh boat to hold projectile on balance
photogate mounting bracket
laptop with capstone software
The ballistic pendulum is an interesting experiment in that it combines multiple physics
principles. A spring launches a ball at the pendulum, which catches and holds it. After the
projectile is fired, the pendulum swings upward through an arc. In the collision between
the projectile and the pendulum, momentum is conserved. After the pendulum catches the
projectile, energy is conserved when kinetic energy is converted into potential energy as the
pendulum swings upwards.
The goal of this lab is to calculate the speed of the projectile as it leaves the launcher. To do
this, you will need to do a number of calculations and use two different conservation laws,
namely the conservation of momentum (during collision) and the conservation of energy
(after the collision).
Conservation of momentum relates the velocity of the ball before the collision with the
velocity of the ball plus the pendulum after the collision using
mb v0 =(mb +mp )vf
Conservation of energy relates the initial (kinetic) energy of the pendulum to the
final (potential) energy using
1⁄ (m +m )v2 =(m +m )gh
2 b p f
where h is the maximum height reached by the center of mass of the pendulum.
Using these two relations, we can determine the velocity, v0, of the ball as it is being shot
from the projectile launcher.
1. Clamp the projectile launcher to the table near the edge. Make sure that the launcher is
perfectly horizontal, and that you do not over tighten the clamp (it needs only be snug
to hold the launcher in place). This step may have been done for you.
2. Slide the rotary motion sensor onto the rod so that the cord on the sensor faces towards
the projectile launcher, and the axle for the pulley faces you. Bring the sensor down the
rod to a comfortable height to work with it (about the middle of the rod) and secure it
to the rod. See the picture below for additional help on how to orient the sensor on the
3. Secure the end of the rod into the lower hole at the point of the heavy base. To do this,
loosen the large screw in the base so the rod will slide into the hole. Make sure the rod
slides all the way into the base (you should hear the thud of the rod hitting the table)
then tighten the screw to secure the rod.
4. Look at the 3-tier plastic pulley that is either on or with the rotary motion sensor. You
want the large side of the pulley to face out. If the pulley needs to be flipped or put
onto the motion sensor, look in the center hole of the pulley and find the raised line.
Make sure the raised line is lined up with the groove in the axle on the rotary motion
sensor, then push the pulley onto the axle. If the pulley won’t slide on easily, ask your
professor for assistance.
5. Find the two raised “notches” on the pulley, this is where the arm/rod of the ballistic
pendulum should sit. Once the arm is lined up you can secure it to the rotary motion
sensor with the screw that is...
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