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Projectile Motion Movie - Prelab

This activity is in preparation for movie making. Imagine tossing a ball, underhand, to a friend, at about a 300 to 400 angle. The friend catches it at the same height as your throw. Assume the origin is your hand and sketch your prediction for the following:

X (horizontal position) vs. t

X

0

Time (s)

Y(vertical position) vs. t

Y

0

Time (s)

x-velocity vs. time

[pic]

Time (s)

y-velocity vs time

[pic]

Time (s)

Draw a motion diagram of the ball, from when it leaves your hand (origin) to just before it hits the floor. Each dot represents a frame in the film (6-8 dots). Label horizontal and vertical axes and add acceleration vectors

[pic]

Projectile Motion Movie

Equipment: Computer, Logger Pro software, Webcam, meter stick, balls, printer cable mouse for computer.

Part 1 - Making the movie

Directions for webcam setup:

Plug the Webcam into either USB port of the computer and bring up Logger Pro.

JUST SAY NO if computer prompts for RightLight.

Insert Video Capture

Under Options, confirm that Picture with standard Analysis is chosen

Under Camera Setting, go to Advanced and:

• disengage AGC

• choose an exposure of 1/100th

• set the gain to about 5000 (about half-way)

1. Make a movie of a ball being tossed. Use a meter stick to set the scale. The meter stick must be at the exact same distance from the camera as the object of interest or it won’t work. Your movie should cover the time from the ball leaving the hand until the ball reaches approximately the same level

2. Choose the 1st point of your motion diagram in the movie as the instant the ball leaves the hand, and set the origin at that point.

3. Add the rest of the points in the motion.

4. Find the time after the movie started when the ball is at the position origin: t = ______s.

5. Make this time t = 0s by making a new calculated column, named tosstime, and use that as the time axis.

Part 2 - Analysis

Print each graph listed below. Each printed graph should include:

• Appropriate title

• Data columns for axes visible (hide unnecessary data columns)

• 1st data point visible at t=0s

• Analysis boxes visible and not covering data

1. Y velocity vs tosstime

Use an appropriate analysis to find values for acceleration and initial Y-velocity. If the last 1 or 2 data points are obviously not good, do not select them for the fit. If the first value is not good, remake the movie. A good toss should show an acceleration magnitude of between 8 and 11 m/s2. If the acceleration is not within these limits, remake the movie.

Find the percent difference between v0y , found in the calculated columns to the left, and the value of the intercept. Use this formula for the comparison:

[|intercept – v0y| / intercept] x 100%

If the value is more than 15% , If not, remake the movie.

Show your work here:

2. X velocity vs. tosstime

Use the appropriate analysis to find the average X-velocity. You may wish to discard the last few data points if they don’t agree with the rest of the data

Find the percent difference between v0x , found in the calculated columns to the left, and the average value. Use this formula for the comparison:

[|average – v0x| / average] x 100%

If the value is more than 15% , remake the movie.

Show your work here:

3. Y vs X graph.

Use the appropriate analysis to find the best-fit equation for this graph. What type of graph is this (eg linear, exponential …..)? Does this agree with the shape of the trajectory shown by your motion diagram in the prelab? If not, explain the discrepancy:

.

4. X position vs. tosstime

Use the appropriate analysis to find the average X-velocity. It shouldn’t be the same as #2. You may wish to discard the last few data points if they don’t agree with the rest of the data. Your value should be reasonably close to the value found in #2.

5. Y position vs tosstime

a. Use the appropriate analysis to find the equation for the height of your ball relative to your hand, at any time. Write this below:

___________________________________________________________

b. What are the physical meanings of the coefficients A, B, C in the equation? Include subscript (x, y)

A:

B:

C:

c. Find the initial speed at which you threw the ball, using your graphs and analysis. Show your work:

v0 =

d Calculate the initial angle at which you threw the ball, using your graphs and analysis. Show your work:

θ =

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