Teacher's guide, Experiment 1: ballistic pendulum – PASCO ME-6815 PROJECTILE CATCHER ACCESSORY User Manual

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Projectile Catcher Accessory

Teacher's Guide

Experiment 1: Ballistic Pendulum

Part I

Generally, determining the velocity of the ball
by the “horizontal-shot” method is more
accurate than using the photogate method, but
the photogate method is quicker and easier.

If you use the photogate method, make sure
that the photogates are parallel.

If you use the horizontal-shot method, make
sure that the gun is perfectly horizontal. Use a
spirit level for best results.

Part II

Setup: Ensure that the string is very loose in
the Velcro assembly. There should be just
enough friction so that that weight of the
string does not pull the string through.

Procedure: It is helpful to anchor the string in
place with a piece of tape (close to the velcro,
on the opposite side from the pendulum) after
firing but before measuring the height reached
by the pendulum.

Notes on Analysis:

The difference between all measured veloci-
ties (by horizontal-shot, photogate, or ballistic
pendulum measurement) should be less than 5%.

Answers to Questions:

1. The theoretical loss is:

For our trials, the theoretical loss was 74.25%.
The actual loss measured was 76.25%. The
excess loss is most likely due to energy lost by
rotational motion of the pendulum. (The motion
of the pendulum is not entirely in the plane of the
pendulum. There is some twisting, which
requires energy.)

2. If the collision is perfectly elastic instead of

perfectly inelastic, the height of the pendulum

increases by a factor of

. It is difficult to

experimentally verify this because the colli-
sion is not perfectly elastic.

Experiment 2: Conservation of Momentum in an Inelastic Collision

Notes on Setup:

1. If you are using the 6500 and gate-pulse mode,

position the Photogate so that it is blocked by the
entire length of the catcher, rather than shining
through the slots.

Notes on Procedure:

2. Make sure that the cart is far enough from the third

photogate that the ball comes to rest relative to the cart
before the cart begins to interrupt the photogate. (5
cm at least.)

3. The computer will give you more numbers than

you need. Motion timer mode (with the 4-1
adapter) will give you four times.

For example:

0.0204 Time for the ball to go between the two Pho-

togates (Use this to calculate ball velocity.)

0.1605 Time between when the ball interrupts the

second Photogate and when the cart inter-
rupts the third. (Ignore this number, it is
meaningless.)

0.1186 Time between leading edge of first cart

segment and leading edge of second cart
segment. (Use this to calculate cart veloc-
ity.)

0.1198 Time between leading edge of second cart

segment and leading edge of third cart
segment. (Can also be used to calculate
cart velocity.)

% lost = 1 –

+ m

x 100%