Let's graph with probes
How do graphs represent motion?

In this activity you will use a motion probe to help you make a graph of Vijay's trip between the Library and the Cinema.

To begin, lay out a "street" in masking tape in a clear area on the floor.

The street should be about 2 meters long and start in front a table or other surface where the probe can be placed as in the picture.


Your teacher's demonstration
Watch your teacher's motion and the shape of the graph produced by the probe and answer the question below.









What did your teacher do and what did you see on the graph?
Draw a prediction graph
The probe graphs motion by plotting "position" as it changes over time. Position is a distance measured from a reference point. The reference point could be any location that we choose, but once we choose it, it is fixed. We will call this reference point position 0 and give it the special name of "origin."

Now, on the graph below draw a line that you think predicts how Vijay's position changes over as he takes his trip from the Library to the Cinema and back. Click on the pencil tool at the right to draw your prediction line. Click on the label tool to add labels about where Vijay is when.
Here is what you need to know to get started: 

• The Library is located at the origin, position 0.
• The distance between the Library and Cinema is 7200 meters.
• Vijay travels from the Library to the Cinema. 
• He takes a few minutes to buy a movie ticket and then returns to the Library.
• The whole trip takes 20 minutes

Click Submit when you are done.

Discuss classmates' prediction graphs
If you clicked Submit on the previous page, you will see some of your classmates' graphs below when your teacher releases them. If the graphs are not yet visible, click the Refresh button. If they still aren't visible, move on to "Defining the reference point" and check back later for results.


What is the difference between your prediction graph and your peers' prediction graphs? What would you change in your prediction graph after discussing your peers' graphs? Explain why. If you would keep your graph the same, explain why.
Thinking about your prediction graph









Your prediction questions results
You will see some of your classmates' submitted answers from the previous page below when your teacher releases them. If they are not yet visible, click the Refresh button. If they still aren't visible, move on to the next step and check back later for results.







Defining the reference point
As you have seen, in order to plot position you need a reference point . For this activity, the reference point is position 0, the origin .

Let's say that the Library is located at the origin.

Vijay starts his trip at the Library then moves to the Cinema, so you also will need to know the Cinema’s position and the direction in which position increases.

For our version of Vijay’s motion we define: 

• The Cinema is 1 meter from the Library. 
• Position increases as we move from the origin toward the probe.

In the next step, you will walk on your masking tape "street" using the motion probe and graph to find the origin.

The origin is at a pre-set distance from the probe, and your task is to find that distance .


Use a reference point to find the library
How will you find the origin on your street? (Recall that the origin is a pre-set distance from the probe.) Try this:

1. Set up your motion probe at the end of a desk or table just in front of the masking tape "street."

2. While watching the graph, start the probe and walk along the street in front of the motion probe until you think you've found position 0, stopping and clearing the graph as needed.

3. Write the word "Library" on a Post-It note and place the note on the "street" at the position of the origin.

4. Then measure or estimate the distance from the origin to the probe, and submit your answer to the question below.

After you submit your answer, you'll be able to see some of the class' answers on the next page after your teacher releases them for viewing.








About how far is the Library from the motion probe? 0 meters .25 to .5 meter .5 to 1 meter 1 to 1.5 meters 1.5 to 2 meters 2 to 2.5 meters 2.5 to 3 meters
Library location results
Your classes' answers for the previous question should appear below. If they are not visible yet, click the Refresh button.



What do you see on the graph when standing at the Library? Nothing changes. Lines and dots jump around on the screen. A line appears on the screen at the end of the movement. A line is slowly drawn across the screen from left to right. 4. A line is slowly drawn across the screen from left to right What do you see when standing at the Cinema?
What do you see when moving back and forth?
How is the graph different when moving more rapidly vs. more slowly?
Walk to the library
Now:
1. Write "Cinema" on a second Post-It note.
2. Find the location of the Cinema and label it. (Remember that the Cinema is 1 meter closer to the probe than the Library.)

3. Then walk Vijay’s trip: In 20 seconds he travels from the Library to the Cinema, buys a movie ticket, and returns to the Library. Walk the trip several times, each time clearing the previous graph and creating a new one. (There's no need to stop the graph. It will automatically stop after 20 seconds.)

Try travelling at different speeds, watching the graph to see how different motions are graphed. Then answer the four questions below and click Submit after answering each.







Graph the trip to the cinema
Now plan and make a final graph of your trip to the Cinema as Vijay did: 
• Vijay starts at the Library and goes to the Cinema. 
• He buys a movie ticket and returns to the Library. 
• The whole trip takes 20 seconds.

Try walking the trip several times, clearing to erase previous graphs, until you have a graph that matches Vijay's trip. Then click Submit to share your graph anonymously with your class.


Discuss classmates' cinema graphs
If you clicked Submit on the previous page, you will see some of your classmates' graphs below when your teacher releases them. If the graphs are not yet visible, click the Refresh button. If they still aren't visible, go on to the next page.


Evaluate classmates' graphs
Have a look at the class' graphs projected in front of your classroom or on the Results page before this page. Please answer and discuss the following questions. You may change your answers after the discussion.


1. Are the graphs all the same? Yes No 2. What is similar about the graphs? 3. What is different about the graphs? 4. If you want everyone's graphs to match, what does everyone have to change or agree on?
Discussing graph results
After you have submitted your answers to the questions on the previous page, you will see some of your classmates' responses below after your teacher releases them. If the answers are not visible, click the Refresh button.


What can a graph tell you about motion?









What was the difference between your graph and your peers' graphs of Vijay's motion? What would you change in your graph of Vijay's trip after discussing your peer's graphs? Explain why. If you would keep your graph the same, explain why.
Results of your motion graph questions
When your teacher releases them, some of your classmates' answers to the previous questions will appear below. If they are not yet visible, click the Refresh button.








The End
Motion Probe Demonstration Page