The Cannon Lab
10
Half-projectiles can be studied to analyze an important factor in projectile motion, the firing
velocity. Using horizontally launched projectile, we can measure the height and the horizontal
range to calculate the time of flight and then working to find the firing speed. This speed can
then be useful if the firing device begins to fire at an angle; thus allowing physicists to predict
heights, ranges and times of flight.
Learning Targets:


Students will study the path of the horizontal projectile for the purpose of
predicting the speed of the cannon.
Students will then extrapolate from that speed, the ranges if the cannon were
fired from multiple angles.
Procedure
A. Finding Initial Velocity
Table 10-1
Height
Time
Horiz. Dist.
Initial Velocity
(m)
(s)
(m)
(m/s)
Class Average
B. The Full Projectile
1. Prior to attempting this part of the lab, use the Vi from Procedure A’s Class Average, and
calculate the “predicted” range for the angle your group is responsible for. Record in
Table 10-2.
2. Using the Vi from Procedure A’s Class Average, calculate the values Vx, Vy, tup, ttotal, and
ymax for your respective angle. Record in Table 10-2 and on the board.
3. Now with the cannon along the counter on the side of the room, adjust the cannon to
the angle your group is responsible for. Place some cardboard at that point you
predicted, load the cannon to the second click and fire. Wherever the marble strikes the
cardboard paper there should be a mark.
4. Circle that mark with a marker and label it with the angle your group fired at.
5. Measure the horizontal range, X, and record in Table 10-2 and on the board.
6. Calculate the % Difference between the ranges using the measured value as the
accepted.
Table 10-2
Angle
Predicted
Range
Measured
Range
(m)
(m)
% Diff
Vx
Vy
tup
ttotal
ymax
(m/s)
(m/s)
(s)
(s)
(m)
10°
20°
30°
40°
45°
50°
60°
70°
80°
7. Draw and label all the above variables on a diagram representing your respective angle.
Interpretation Questions
1. In Procedure A, if you were to change the height of the cannon, would the horizontal
VELOCITY change? Explain.
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2. In Procedure A, if you were to change the height of the cannon, would the horizontal
DISTANCE change? Why or why not?
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3. Based on Procedure B, at what angle will a projectile travel its furthest possible range,
assuming the launching velocity remains constant?
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4. Even though we fired at numerous angles, do any of the distances look similar? If so,
which ones?
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5. What conclusions can be made about the horizontal range and the angles it is fired at?
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6. Explain how a projectile launched at 10° and one launched at 80° have the potential to
land in the same place. If you were to visualize their trajectories, what major differences
would there be (refer to your data if need be)?
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Extension