CONCEPTUAL PHYSICS Experiment
Projectile and Satellite Motion: Projectile Motion
A Projectile Puzzle You Can Solve
Bull's Eye
Purpose
To predict the landing point of a projectile
Apparatus
1/2" (or larger) steel ball
table
empty can
meterstick
stopwatch
means of projecting the steel ball horizontally at a known velocity
Discussion
Figures 10.3 and 10.4 in Conceptual Physics show how projectiles move with constant speed in the horizontal direction while undergoing free-fall acceleration in the vertical direction. Figure 1 at the right shows the same for a ball tossed horizontally. The horizontal and vertical motions are independent of each other!
Instead of tossing a ball from a cliff, you'll fire a steel ball off the edge of a table and into a can on the floor below—all without a trial shot!
When engineers build bridges or skyscrapers, they do not do so by trial and error. For the sake of safety and economy, the effort must be right the first time. Your goal in this experiment is to predict where a steel ball will land when projected horizontally from the edge of a table. The final test of your measurements and computations will be to position an empty can so that the ball lands in the can on the first attempt.
Procedure
Step 1: Your instructor will provide you a means of projecting the steel ball at a known horizontal velocity (it may be a spring gun, a ramp, or some other device). Position the ball projector at the edge of a table so the ball will land downrange on the floor. Do not make any practice shots (the fun of this experiment is to predict where the ball will land without seeing a trial). Figure 2 shows the quantities involved in this experiment.
v is the horizontal launch speed of the ball
y is the vertical distance that the ball falls during its flight—from the table to the top of the can
x is the horizontal distance the ball travels during its flight