Projectile motion is motion in two dimensions under the influence of a constant force.
It is hard to get detailed information about its motion without using external
measuring instruments. In this experiment the instrument is a video
camera. You will analyze a video clip. The clip shows a person
throwing a ball. You will determine the position of the ball in two
dimensions as a function of time by stepping through the video clip
frame-by-frame and by reading the time and the position coordinates of the ball
off each frame. You will construct a spreadsheet with columns for time and
position and use this spreadsheet to find the x and y component of the velocity
as a function of time.
To play the video clip or to step through it frame-by-frame click the "Begin" button. The "Video Analysis" web page will open. Choose one of the throw_x.avi video clips.
- "Play" the video clip. When finished, "Step up" to frame 0
- In the setup window choose to track both coordinate of the object.
- Click "Calibrate". Click "Calibrate X". Calibrate the x-axis as in lab 1. Then click "Calibrate Y". Calibrate the y-axis as in lab 2.
- Click the button "Click when done calibrating". A spreadsheet will open up. Click "Start taking data".
- Start tracking the ball. Position the cursor over the ball. When you click the left mouse button, the time and the x- and y-coordinates of the ball will be entered into the spreadsheet. You will automatically step to the next frame of the video clip. When done, click "Stop Taking Data".
- Your table will have 3 columns, time (s), x( m), and y (m).
- Open Microsoft Excel, and paste the table into an Excel spreadsheet.
Produce graphs of the x and y components of position versus time. Label the axes.
- Describe the graphs? Does one of the graphs resemble a straight line? If yes, what does this tell you?
- Right-click your data in the x(m) versus time graph and choose "Add Trendline". Choose "Type, Linear" and "Options, Display equation on chart". An equation y = ax + b will appear on your graph, where the number a is the slope and the number b is the y-intercept. What is the physical meaning of the slope of this graph?
- Right-click the data in your y(m) versus time graph and choose "Add Trendline". Choose Polynomial, Order 2 and under options click "Display equation on chart". An equation of the form y = b1x2 + b2 x + b3 will be displayed where b1, b2, and b3 are numbers. What do the coefficients b1 and b2 tell you?
- We can view the motion of a projectile as a superposition of two independent motions. Describe those two motions.
Paste your graphs with trendlines into your log.