012-06379B
Photogate Timer
9
®
Experiment 3: Speed of a Projectile
Figure 3.1: Equipment Setup
Ramp
Mark with pencil
Photogate
LED comes ON
LED goes OFF
Figure 3.2: Measuring
Δ
Δ
Δ
Δ
Δ
d
Accessory
Photogate
Ramp
Ball
EQUIPMENT NEEDED:
-Photogate Timer, with Accessory Photogate
-Ball and ramp
-Meter stick
-Plumb bob
-Carbon paper
Introduction
Projectile motion adds a new dimension, literally, to experiments in linear accelera-
tion. Once a projectile is in motion, its acceleration is constant and in one direction
only—down. But unless the projectile is fired straight up or down, it will have an
initial velocity with a component perpendicular to the direction of acceleration. This
component of its velocity, since it is perpendicular to the applied force of gravity,
remains unchanged. Projectile motion is therefore a superposition of two relatively
simple types of motion: constant acceleration in one direction, and constant velocity
in an orthogonal direction.
In this experiment you will determine the initial velocity of a projectile directly,
using the Photogate Timer, and compare that with a value calculated by examining
the motion of the projectile.
Procedure
c
Set up the apparatus as in figure 3.1, so the
ball rolls down the ramp onto the table, then
passes through the photogate, interrupting
the beam.
d
Tape a piece of paper to the table, under the
Accessory Photogate. Use the ramp to push
the ball slowly through the Accessory
Photogate, as shown in Figure 3.2. Deter-
mine the point at which the ball first triggers
the Photogate Timer—this is the first point at
which the LED turns ON—and mark it on
the paper. Then determine the point at which
the ball last triggers the timer, and mark this
point also. Measure the distance between
these marks and record this distance as
Δ
Δ
Δ
Δ
Δ
d
.
Replace the ramp as in Figure 3.1.
e
Use a plumb bob to determine the point
directly below where the ball will leave the
edge of the table after rolling down the ramp.
Measure the distance from the floor to the
top of the table at the point where the ball
leaves the table and record this value as
d
y
.
f
To measure the position where the ball will
strike the floor after rolling down the ramp,
tape a piece of plain paper onto the floor with a piece of carbon paper on top. The
impact of the ball will leave a clear mark for measuring purposes.
Ramp
