Cunningham, Mary M. Resurrection High School

OBJECTIVES To measure muzzle velocity of a projectile device. To predict maximum range of a projectile device at various angles. To measure range of device at various angles. APPARATUS NEEDED Calculator, Tape measure, stopwatch, projectile device, projectiles. (This demonstration used a "Lobster," a device used in training tennis players.) RECOMMENDED STRATEGY 1. Throw a ball or frisbee out to groups of students. Ask students to toss the ball back and forth. Have students jot down their observations and and a description of the motion of the ball. 2. Introductory discussion: What name could we give to this category of objects? (PROJECTILES) Can you think of some other projectiles? What are some of the characteristics of projectiles in motion? (List all suggestions on board or overhead. If necessary elicit the following terms: velocity, acceleration, time, horizontal motion, and vertical motion. 3. Explanation: In order to analyze projectile motion with all the listed characteristics, we would need a NASA computer. We are going to ignore all factors except velocity, acceleration and time. If necessary review horizontal velocity and vertical velocity. 4. Presentation of activity: a. Work in lab groups. b. Explain use of the projectile device. The muzzle velocity can be determined by aiming the muzzle straight up. Record the time required for the projectile to leave the muzzle and return to the ground. Do 5-10 trials, find the average round trip time. c. Choose 2-3 angles. Predict the range using vector analysis and trig calculations. (See Math Notes) Use the projectile device, measure the range of the projectiles. Compare projected range with actual range. What are the sources of error? (Consider using complementary angles) 5. Post activity discussion: Explain why there were differences between predicted and experimental value of range. What were the variables? How could variables be controlled? What conditions would optimize experimental values? How could experiment be improved? What other ways could projectile motion be tested? NOTES 1. Non-Math oriented classes: This activity can be modified for use with students who are not in high school physics. Students could be asked to predict which angle will make the ball go further. They can begin with actually testing the device and could graph the angle vs. distance shot. 2. Math Notes Muzzle Velocity V(muz) = A * T Where A is the acceleration of gravity and
T is half the round trip time for a ball
shot directly upward.

Range Calculations The muzzle velocity does not change as the angle is changed. It
can be resolved into a vertical and horizontal component.
Consider the angle with the horizontal to be Theta then
V(ver) = V (muz) * sin Theta and
V(hor) = V (muz) * cos Theta The time of flight can be calculated using the formula, V(ver) = A * Tup and solving for Tup.
Time of flight is 2 * Tup.
Since the V(hor) is not accelerated,
Range = V(hor) * time of flight
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