Relative Velocity Lab Directions:

You will be using a pre-made video to explore relative velocity with the video analysis tools in logger-pro. Using the tools in logger-pro you will plot the motion of the car and the board and analyze these motions with respect to each other and with respect to the ground. Logger-pro will plot the motions of the objects with respect to the ground. It will be up to you to figure out how to find the motion of the car with respect to the board. Have fun!!!

Go to my website and download the video: Click on the link for honors physics, right click on the link that says “relative velocity video,” select “save target as,” and save it on your computer.

Open Logger-Pro and insert the video.

You will analyze the videos using the same basic methods that you used in the 2D lab with the video camera and tennis ball. There is one additional button that will be needed for this lab, which allows you to plot the motion of a second object in the picture. This button is circled in yellow below. Plot the motion of the first object and then click on the button circled and select “add point series.” This will give you a different color dot to use for the other object.

There is no need to set an origin because the automatic setting works for this lab. You do need to set the scale using the meter stick in the frame. Use the 4th button from the top to do this.

Activity 1 - Analyze frames 1658 – 1701 of the video. There is an arrow on the picture above pointing to the place the frame number is shown. In this activity we are looking at the motion in the x-direction and neglecting the motion in the y-direction.

1.Plot the motion of the car and the board using the method described above.

2.Double click on the top of each column of position data and name it properly.

3.The graph should show the x-direction position of the board and the x-direction position of the car. To select what data is shown on the graph click on the y-axis label. Select “more….” Check the boxes for the x-direction position of the board and the x-direction position of the car.

4.Now make a calculated column with the position of the car with respect to the board. When we find the position of the car with respect to the moving board we want to know how far apart the dot on the board and the car are at every time interval.

5.Click on the y-axis labels and check the box of your new calculated column so that you have three lines on the same graph.

6.Do linear fits on all of the graphs. Your page should look like this:

7.Answer the following questions:

a.What is the board’s velocity relative to the ground?

b.In what direction is the board traveling?

c.What is the car’s velocity with respect to the ground?

d.In what direction is the car traveling?

e.What is the car’s velocity relative to the board?

Save this file but do not print. You will print it after Ms. Meyer approves it.

Activity 2: Use the directions above to analyze the frames 2778-2806. In this activity we are neglecting the motion in the y-direction. We only care about the motion in the x-direction. Be sure to answer the questions listed above for this activity as well.

Save this file but do not print. You will print it after Ms. Meyer approves it.

Activity 3: For this activity you will analyze frames 299-333. We are now dealing with velocity in both the x and y directions. This situation is similar to problems in which a boat crosses a river.

  1. Use the directions above to analyze the video.
  2. Make a position vs. time graph containing the x-direction motion of the car and the board. This graph should have two lines.
  3. Make a position vs. time graph containing the y-direction motion of the car and the board. This graph should have two lines.
  4. Answer the following questions.
  5. What is the car’s velocity relative to the board?
  6. What is the board’s velocity relative to the ground?
  7. What is the car’s velocity relative to the ground?

Save this file but do not print. You will print it after Ms. Meyer approves it.

Activity 4: In this activity you will be analyzing frames 299-344 the old fashioned way.

  1. Open a new logger-pro file.
  2. Insert the video.
  3. Tape an overhead to the screen of the computer so that it covers the video on the screen. Do not place the tape on the actual screen of the computer. Use the tape on the plastic rim of the screen only.
  4. Draw a line on the meter stick in the picture. You will use this to set the scale.
  5. At frame 299 use a blue marker and place a dot on the car. Use a red marker and place a dot on the board dot.
  6. Advance the video 5 frames.
  7. Repeat steps 4 and 5 until you get to frame 344.
  8. Take the overhead off of the screen and obtain a ruler.
  9. Measure the distance between the first blue dot and the first red dot. This is the distance between the car and the board dot at time t=0. Record these values in a data table.
  10. Measure the distance between the second blue dot and the second red dot. This is the distance between the car and the board at t = (the time for 5 frames, which you can figure out). Record these values in a data table.
  11. Continue measuring the distance between the red dots and the blue dots as instructed in steps 7 and 8. Record the values in a data table.
  12. Use Logger-Pro to make a graph of the distance between the car and the board dot vs. time to find the velocity of the car with respect to the board.

Save this file but do not print. You will print it after Ms. Meyer approves it.

Activity 5: Find the percent difference between the velocity of the car relative to the board for activities 3 and 4.

- % difference = (difference of values)/(average of the two values)