G Pandemic COM Lab

Introduction:

When a moving airtrack glider strikes and sticks to a stationary one, the velocity predictably goes down, because the total momentum must remain constant, but the mass increases, so therefore the velocity must decrease:

(small mass)(big velocity) = (big mass)(small velocity) or something like that.

So in this lab we are testing whether momentum is actually conserved. We will do this by calculating the momentum before and after a collision on a frictionless track. Of course when we take data in a laboratory setting, there will be small (or large) errors in our data, so our momentum before and after will not be exactly the same, so we must calculate what the range of momentum was before, and calculate what the range of momentum was after, and see if they overlap.

Rationale for the Lab:

For this lab, you must turn in:

• A data table with the masses and velocities of the gliders before and after. Your velocities should be expressed as an average, a maximum, and a minimum.

• Your calculations of the range of possible momentums before, and after (There will be 6 total calculations)

• A conclusion where you make a mathematical argument (Citing data specifically) as to whether the momentum before and after could have overlapped or not

My suggestion is to make a Google Doc, but insert photos of your calculations on a sheet of paper. You could do the whole thing as a Google Doc.

Directions:

1. Use the Vernier Video Analysis app to analyze one of the collision videos at the bottom of this page. (See video, and separate directions)

2. Put all your data in a nice, neat data table that has units. Your data table should have the masses of the gliders in your video, as well as the min, mean, and max velocity of the first glider before the collision, as well as the same for both gliders after the collision.

3. Calculate the minimum, average, and maximum momentum before the collision. (The mass of the first glider times its velocity)

4. Calculate the minimum, average, and maximum momentum after the collision. (The mass of the both gliders times their velocity)

5. Make a mathematical argument citing data as to whether the momentum before overlaps the momentum after.

There are help videos at the bottom of the page

Mass Data for Pandemic: (The letters should be clearly visible in the videos)

Glider A: 300.0 +/- 0.05 g

Glider B: 291.2 +/- 0.05 g

Glider C: 143.4 +/- 0.05 g

(We will neglect the uncertainty of the masses because it is so small)

Video Analysis Directions (For Chromebook)

1. Pick a movie from the bottom of this page. AB movies are two red carts of equal size, BC is a big red glider running into a small yellow glider, and CB videos are a small yellow glider running into a big red glider.

2. Download the movie file to your Drive by clicking the download link below. Save it to your Google Drive. (should do that automatically on a Chromebook)

3. Go to this document <Here> and go to the link. This will run the Vernier Video Analysis web App. (You must be signed into your ttsdstudents.org account)

4. Click where is says "CHOOSE FILE" and go to where you stored it on your Google Drive and you should see a lovely video of the collision you chose.

5. On the left side of the video, click the little "1.0 SCALE" button. It will bring up a tool. Drag the tool so that the black scale line goes from the left to the right side of the Meter stick that is below the airtrack. Type that this distance is 1.00 m in the two boxes. (1.00 in the first box, m in the second)

6. Now click on the gear button on the lower right side of the video screen, and set it to advance 5 frames for every data point. (This is so we don't have 10 billion data points, only about 60.) Close the settings dialog box.

7. Now choose the "ADD" button on the top left side. The cursor will become a crosshairs when is is over the video. Make sure the movie is at the beginning, and now we are ready to take data. The app will record in the data table the position x and y, as well as the time for every click you make, and then advance the video for you. It also will place a little dot on the video that becomes less and less helpful as the dots get closer together (i.e. you can't see through the dots - spoiler alert) So what I do is I line up the bottom of the crosshairs above a little white nut that is on the side of the glider.

8. Play the movie and figure out when I release the glider, and back it up to that point. Now we are ready to take data!!

9. Put the bottom of the crosshairs on the left side of the moving glider and click. The movie will advance 5 frames. Click again, and repeat until the two gliders stuck together hit the end of the track. Stop clicking before it strikes the end.

10. When you are done clicking, make the graph as big as possible by choosing the layout icon, and selecting only the graph. Change the axes to X velocity vs. time (Click on the y axis label) and select the velocity range before the collision. Click on the graph icon on the bottom left of the graph, and choose "View Statistics". This will pop up a little window that has your mean (average), maximum and minimum values. Write these down, or screen shot them. Do the same thing for the velocity range after. Be sure to avoid the region where the velocity is changing.

Help Videos:

1. Doing Video Analysis:

2. Making a neat data table:

3. Calculating the momentums:

4. Making a mathematical argument as to whether the momentum before and after overlap: