PhysicsLAB: Video LAB: Ball Re-Bounding From a Wall

Background and Purpose

This lab is based on the video entitled Ball re-bound from the Direct Measurement Video Project hosted at Science Education Research Center at Carleton College (SERC). The copyright for these videos belongs to School District 197 in Mendota Heights, Minnesota. The project is partially funded by a National Science Foundation Grant #1245268 awarded in September 2013.

The following lab implementation was designed for use in my Honors Physics I class and only represents one method of analyzing the data provided in the video. Before taking any measurements, view the video several times to acquaint yourself with its scenario.

Our data collection and analysis is based on three phases of the ball's motion in the video.

the motion of the ball before it contacts the wall
the ball's impact with the wall
the motion of the ball after it leaves the wall

Our purpose is to calculate the impulse delivered to the ball by the wall.

Procedure

Restart the video and open the horizontal ruler tool. Please the value of 24 cm on the edge of the wall. Then step through the video so that the left edge of the ball's diameter is as close as possible to the 0-position of the ruler. When everything has been aligned, add the stopwatch and reset it to 0.00000 seconds - this will also set the frame to 0.

Record your information in the following table.

starting position	frame number	position of left edge of ball	position of right edge of ball	time
(cm)		(cm)	(cm)	(sec)
	0	0		0.00000

Now slowly progress the video forward until the right edge of the ball just makes contact with the wall. Record your data in the chart below.

touches wall	frame number	position of left edge of ball	position of right edge of ball	time
(cm)		(cm)	(cm)	(sec)
			24

Now slowly step the video forward through the entire impact of the ball with the wall stopping when the right edge of the ball just loses contact with the wall. Record your data in the chart below.

after impact	frame number	position of left edge of ball	position of right edge of ball	time
(cm)		(cm)	(cm)	(sec)
			24

The last set of data occurs when the left edge of the ball returns to the 0-position on the ruler.

returns to start	frame number	position of left edge of ball	position of right edge of ball	time
(cm)		(cm)	(cm)	(sec)
		0

Analysis

Refer to the following information for the next five questions.

Before proceeding further, we are going to verify that you have correctly recorded your times for each completed phase. The video was recorded at 960 frames/sec.

Calculate how many seconds pass between each successive frame on this video.

Since you reset the stop watch to zero at the beginning of your data collection, you can now verify the time on the stop watch. You will do this for the third data chart which represents when the ball first lost contact with the wall right after impact.

(a) What was the frame number?

(b) What was the stop watch's value for the time?

Do these two values agree? If not, return to the video and recollect data.

yesno

Refer to the following information for the next six questions.

Since the video was filmed in slow motion, it is reasonably safe to assume that the velocity of the ball before impact and the velocity of the ball after impact do not represent an interval of accelerated motion. Therefore we can calculate these velocities using the constant velocity equation of s = vt. Remember that both velocities can not be positive since in one instance the ball is moving towards the right and in the other the ball is moving towards the left.

How many seconds passed between the ball's starting position on the video (when you zeroed the stop watch) and when the ball initially made contact with the wall? Express your answer in seconds to 5 decimal places.

How far did the left edge of the ball move to the right during that time? Express your answer in meters to three decimal places.

What was the ball's initial velocity (in m/sec) before it touched the wall?

How many seconds passed between the ball losing contact with the wall and when it returned to its initial starting position? Express your answer in seconds to 5 decimal places.

How far did the left edge of the ball move to the left during that time? Express your answer in meters to three decimal places.

What was the ball's final velocity (in m/sec) after it bounced off the wall?

Refer to the following information for the next six questions.

We are now going to calculate the values for the ball's initial and final momentums. That information will then allow you to determine the impulse that the wall delivered to the ball during impact.

What is the formula to calculate an object's momentum?

Is momentum a scalar or vector property?

scalarvector

What was the ball's mass in kg?

What was the ball's initial momentum before impacting the wall?

What was the ball's momentum after it rebounded from the wall?

What impulse did the wall deliver to the ball while they were in contact?

Refer to the following information for the next three questions.

We are almost done with our analysis. We now need to calculate the average force that the wall exerted on the ball and the ball's acceleration during its contact with the wall.

How much time did the ball remain in contact with the wall? Express your answer to 5 decimal places.

What was the average force that the wall exerted on the ball while they were in contact?

What was the ball's average acceleration while it was in contact with the wall?

Refer to the following information for the next six questions.

The work done on an object is defined by the change in the object's kinetic energy, KE = ½mv². We are now going to determine if any work was done on the ball by the wall.

What was the ball's original KE before hitting the wall?

What was the ball's final KE after it rebounded off the wall?

Did the ball's KE change?

yesno

Did the wall do any work on the ball during their collision?

yesno

If you answer above is yes, calculate how much work was done on the ball.

Based on the ball's compression while in contact with the wall, is your previous answer regarding work done on the ball by the wall what you expected? Explain.