IB Conservation of Momentum Lab

The Lab Handout: Lab-ConservationOfMomentum.pdf

When a moving glider strikes a glider at rest on an air track the velocity will go down, but momentum will be conserved. Here you will test this. We will determine the velocity before and after the collision using an ultrasonic range finder.

Directions:

1. You will need one lab partner, (Work in groups of 2 – if you have a group of 3 then you must analyze two different collisions), an air track, two gliders, and a computer with Logger Pro on it.

2. Mass the two gliders and record this. Level the air track. Practice the collision (Not too fast, not too slow) – it sometimes helps to hold the stationary glider still with a finger until just before the collision. For the calculations, you will need to gather the mass of both gliders, and the velocity of the gliders before and after, and the uncertainty of everything you measure.

3. Run the momentum lab on the desktop. You will need to adjust the rangefinder until you get a nice graph of the collision on your velocity graph. When you get the graph you want, you can use “Analyze” > “Statistics” and it will pop up a neat balloon on your graph that has the information you need. (Including uncertainty!)

4. With the statistics showing, you can print your graph from the computer. You only need one copy, as the two of you can turn in one lab.

5. Make a nice neat data table, and calculate the momentum and the uncertainty of momentum before and after the collision.

6. Write an appropriate IB conclusion.

Here's what you turn in:

1. A printout of your collision graph with the statistics balloons showing.

2. A nice data table that has the information you used in your calculations. (units and uncertainties)

3. 3. Your calculations of the momentum before the collision, and after the collision and the uncertainty of those momenta.

4. An appropriate conclusion and evaluation of the experiment as per IB criteria.

   1. Use the numbers to make an argument as to whether the data you have disproves conservation of momentum. You will need to intelligently use the uncertainties, as well as the calculated momenta before and after.

   2. Discuss the sources of error present, and what effect those source might have had on the investigation

   3. Suggest ways to improve the procedure to eliminate the sources you mentioned

Watch this these if you have questions about how to analyze the data and write up the lab:

Old stuff:

Pandemic 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 uncertainty of momentum was before, and calculate what the uncertainty of momentum was after, and see if they overlap.

1. 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, an uncertainty

• Your calculations of the momentum before, and after.

• Your calculations of the uncertainty of the momentum before and after. (There will be two different uncertainties)

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

• Identify three sources of error in the lab.

• Suggest (for each source of error) specifically how you would correct for or reduce that source of error. Do not invent robots at this point please.

You can either do it on paper neatly (pen or pencil), or use a google doc. If you are using Google Docs, make your calculations look nice by using the equation editor.

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 and their uncertainties of the gliders in your video, as well as the mean velocity and the uncertainty of the velocity of the first glider before the collision, as well as the same for both gliders after the collision.

3. Calculate the momentum and uncertainty of the momentum before the collision. (The mass of the first glider times its velocity)

4. Calculate the momentum and uncertainty of the 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.

6. Write the bit about error and improvements. (above)

7. Submit it neatly with pen or pencil, or as a pdf of a Google doc.

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

(The uncertainty of the masses is half the smallest division on the triple beam balance I used to measure them)

Movie Files (It doesn't matter which one you pick)

• • AB1.mp4

  • AB2.mp4

  • AB3.mp4

  • BC1.mp4

  • BC2.mp4

  • BC3.mp4

  • CB1.mp4

  • CB2.mp4

  • CB3.mp4

The naming system here is that AB1 means the first trial of A hitting B, where A and B are the gliders labeled in the video, and 1 is the trial number. (You only have to do one of the trials)

Video Analysis Directions (For Chromebook)

1. Pick a movie from the above. 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. They all should be fine.

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 "System" then 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. Click the Origin tool and make the airtrack parallel to the x axis. (We are gong to use velocity, so the position is not important)

7. 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.

8. 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.

9. Play the movie and figure out by going forwards and backwards 5 frames at a time when I release the glider, and back it up to that point. Now we are ready to take data!!

10. 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. You want as many clicks and dots after the collision as there were before, so usually you can stop when this happens.

11. 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. Be careful to select only the dots before the collision. Avoid the dots that are during the collision or after. 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 careful to select only the dots after the collision. Avoid the dots that are during the collision or before. Be sure to avoid the region where the velocity is changing.

Help Videos:

2. Doing Video Analysis:

3. Making a neat data table:

4. Calculating the momentums:

5. Calculating the Uncertainty:

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

7. Making the Equations in Google Docs: (you don't have to use Google docs, but if you do...)