PASCO ME-6831 Ballistic Pendulum_Projectile Launcher - Manual (Page 41)

®
M o d e l N o . M E - 6 8 3 0 E x p . 8 : P r o j e c t i l e V e l o c i t y — A p p r o x i m a t e M e t h o d
0 1 2 - 0 5 3 7 5 C 37
Exp. 8: Projectile Velocity—Approximate Method
Equipment Needed
Purpose
The muzzle velocity of the projectile launcher is determined by launching the ball into the ballistic pendulum and
observing the angle to which the pendulum swings.
As derived earlier in the manual, the equation for the velocity of the ball is approximately:
where M is the mass of the pendulum and ball combined, m is the mass of the ball, g is the acceleration due to
gravity, R
cm
is the distance from the pivot point to the center of mass of the pendulum, and
 is the angle reached
by the pendulum after the collision.
Setup
1. Put the Projectile Launcher on the Ballistic Pendulum upright at the level of the ball catcher (the low posi-
tion). Make sure that the pendulum can hang vertically without touching the launcher.
2. Clamp the Ballistic Pendulum base to a sturdy table. Make sure that the clamp does not interfere with the pen-
dulum swing.
Procedure
1. Latch the pendulum at 90° so it is out of the way temporarily, and then load the projectile launcher with the
steel ball. Allow the pendulum to hang freely, and move the angle indicator to zero degrees.
2. Fire the launcher and record the angle reached. If you want to do the experiment with a lower or higher angle,
add to or remove mass from the pendulum. Repeat these test measurements until you are satisfied with the
mass of the pendulum.
3. Once you have chosen the mass to use for your experiments, remove the pendulum from the upright by
unscrewing and removing the axle. Use a mass balance to find the mass of the pendulum and ball together.
Record this value as M in Table 8.1.
4. Measure the mass of the ball alone and record this as m.
• Tie a loop in a piece of string, and hang the pendulum horizontally from the loop. (See Figure 8.1.) With the
ball latched in position in the ball catcher, adjust the position of the pendulum in the loop until the pendulum
balances. Measure the distance from the pivot point to this balance point, and record the distance as R
cm
..
Item Item
Ballistic Pendulum/Projectile Launcher Steel ball
C-clamp Mass balance
String
v
b
M
m
----- 2gR
cm
1

cos –
 
=
String loop
R
cm
Figure 8.1: Setup