PhysicsLAB: Video Lab: Ball Bouncing Across a Stage

This lab is based on a Direct Measurement Video called Ball Bouncing Across a Stage released on the Science Education Research Center (SERC) website. The copyright for this video belongs to Independent School District 197 in Mendota Heights MN. The project is partially funded by a National Science Foundation Grant (#1245268) awarded in September 2013.

The following lab directions were designed for use in my Honors Physics I class and only represent one method of analyzing the data provided in the video.

Note that this video was filmed at _____ frames per second. Since there is no stopwatch feature, you will have to use the frame rate to determine time differences.

NOTE: when projectiles are moving both forward (horizontally) and up/down (vertically) the values of their velocities are NOT RELATED. That is, the projectile’s horizontal speed does NOT influence, in any way, the instantaneous values of any of its vertical velocities.

Part I. Horizontal Motion

When the video opens, it is on frame:+0. Press play and view the entire scenario. Note the following special frames:

On frame:+64, the ball is centered on the right vertical post.
On frame:+170, the ball is center on the left vertical post.

(a) Determine the amount of time in seconds that passes between frame:+64 and frame:+170. Show your calculations on your paper.

(b) Calculate the horizontal speed of the ball (in m/sec) as it travelled between the poles. Show your calculations on your paper.

Refer to the following information for the next two questions.

After initially scaling your screen, do not make any changes to its size during this section.

(c) Use a ruler to measure the length of the distance between the poles, labelled in magenta as 3 meters. Record your answer to the nearest 10th of a centimeter

Calculate the conversion factor between your centimeter measurement and an actual meter on the physical stage. Show your work on your paper.

Part II. Vertical Motion

(d) Now, using the same ruler step to frame+64 and measure the distance between the base of the yellow (right) pole and the base of the green ball to the nearest 10th of a centimeter.

Convert your vertical measurement from centimeters to meters.

(e) Now, using the same ruler step to frame+170 and measure the distance between the base of the beige (left) pole and the base of the green ball to the nearest 10th of a centimeter.

Convert your vertical measurement from centimeters to meters.

You are now going to use the kinematics equations for uniformly accelerated motion to calculate the ball's vertical displacement, the ball's initial vertical velocity, and the ball's final vertical velocity.

At this junction in the lab you have the measured and calculated the following data.

a = -9.8 m/sec²
t = (answer to part a - in seconds)
h_o = (answer to part d - in meters)
h_f = (answer to part e - in meters)

Refer to the following information for the next five questions.

Analysis

(f) What was the ball's net vertical displacement between frame+64 and frame+170.

(g) Determine the green ball’s initial vertical velocity in m/sec as it passed in front of the yellow (right) pole. Show your calculations on your paper.

(h) Determine the green ball’s final vertical velocity in m/sec as it passed in front of the beige (left) pole. Show your calculations on your paper.

(i) Step through the video between frame:+64 and frame:+170 and determine the frame number when the ball reached its apex.

Is the frame number in (i) half way between frame:+64 and frame:+170?

yesno

Refer to the following information for the next question.

Conclusion: You are now going to discuss the inter-relationships between your answers obtained during the Analysis section of the lab.

Based on your answers to the questions f through I, explain why v_o and v_f should NOT be equal.