250 3-1
EXPERIMENT 3
PROJECTILE MOTION
I. THEORY
The purpose of this experiment is to measure the initial velocity of a ball that is fired
from a projectile launcher (spring gun) by measuring its horizontal and vertical
displacement. You will use the equations of motion for projectile motion to calculate the
initial velocity.
II. LABORATORY PROCEDURE
Note: You must wear safety glasses for this lab.
1. Clamp the Projectile Launcher at the end of one of the fixed lab stations. Your instructor
will demonstrate how.
2. Set the Projectile Launcher to an angle of 30.0°.
3. There is a picture of the ball near the end of the launcher. We will consider this picture to
coincide with the initial position of the ball when it begins its free fall motion. Measure
the distance from the bottom of the ball pictured on the side of the launcher to the floor of
the lab room. Make sure your meterstick is vertical! This will be the starting height of the
projectile.
4. For measuring the horizontal displacement of the ball, it is useful to place a small piece
of blue painter’s tape on the floor with a dot marking the point directly below the bottom
of the ball pictured on the side of the launcher.
5. Use the rod provided with the projectile launcher to push the plastic ball into the
projectile launcher. For the entire experiment the short range on the projectile launcher
will be used for all runs. Be sure the indicator bar is in the appropriate position. NOTE:
The projectile launcher will sometimes launch the ball unexpectedly. Never look into the
barrel of the loaded projectile launcher or have your face close to it. After loading, check
that the angle is still set to 30.0°. You should perform this check each time you load the
ball.
6. Place a two-meter stick on the floor with its zero centimeter mark on the dot on your blue
tape. Launch the ball. If your meterstick is well aligned with the path of the ball, the ball
will strike it or very near to it. Adjust the meterstick so that the ball hits the ground very
near to it. (You may have to reload and fire the projectile several times.)
7. Now you will make 3 measurements of the horizontal displacement. Load the ball and
fire as before. One group member should watch for where the ball strikes the ground and
estimate the reading on the meterstick to the nearest 1 cm. Your 3 measurements should
be within about 5 cm of each other. If they are not, consult your instructor.
8. Repeat steps 2 through 7 for an angle of 60.0°.
