On Target
Purpose: To investigate the independence of horizontal and vertical components of motion and to predict the landing point of a projectile.
Equipment:
Ramp or Track
Steel ball
Empty soup can or container
Meter stick
Plumb line
Stopwatch or Photo gates timers
Discussion: The equation for distance traveled when motion is uniform is x = vt.
The equation for speed horizontally is v = x / t
The equation for vertical distance, y, fallen after any time t is y = ½ g t2.
The falling speed v after any time t is v = g t
Procedure:
1. Assemble your ramp. Make it sturdy so the steel ball rolls smoothly and reproducibly. The ramp should not sway or bend. The ball must leave the table horizontally. Make the horizontal part of the ramp at LEAST 50 cm long. The vertical height of the ramp should be at least 30 cm.
2. Use a stopwatch or photo gates to measure the time it takes the ball to travel, from the first moment it reaches the level of the tabletop to the time it leaves the tabletop. Divide this time interval by the horizontal distance on the ramp to find the horizontal speed. Release the ball from the same point on the ramp for each of 3 trial runs.
3. Do NOT permit the ball to strike the floor. Record the average horizontal speed from the 3 runs.
4. Using a plumb line and a string, measure the vertical distance, h, the ball must drop from the bottom end of the ramp in order to land in an empty soup can on the floor.
5. Using the appropriate equation from the discussion, find the time t it takes the ball to fall from the bottom end of the ramp and land in the can. Write the equation that relates h and t.
6. The range is the horizontal distance of travel for a projectile. PREDICT the range of the ball. Write the equation you used and your predicted range.
7. Place the can on the floor where you predict it will catch the ball.
8. Test your prediction making certain to release the ball from the same height as in your previous trials.
Analysis:
1. Should the height of the can be taken into account when measuring the vertical distance, h? If so, make your measurements accordingly.
2. Compare the actual range of the ball with your predicted range. Compute the percentage error.
3. What may cause the ball to miss the target?
4. You probably noticed that the range of the ball increased in direct proportion to the speed at which it left the ramp. The speed depends on the release point of the ball on the ramp. What role do you think air resistance had in this experiment?
Data:
Horizontal Distance: ______m
Horizontal Time: ______s, ______s, ______s
Horizontal speed: ______, ______, ______
Average horizontal speed vx = ______
Vertical distance, h = ______
Equation for vertical distance relating h and t; t = ______
Equation for range: ______
Predicted range, R = ______Signed ______
Actual Range: ______
Calculate Percentage Error: ______
Conclusion: