Background:

The change in velocity of an object is often described as its acceleration. Recall that the change in position of an object from moment to moment is expressed as velocity (metres per second). The change in velocity of an object from moment to moment is expressed as acceleration. Describing the acceleration of an object is easier if you are able to reliably record the velocity of the object is at regular intervals. This can be accomplished with a motion sensor:

A motion sensor sends position data to a computer, which then plots data points on a velocity-time graph, representing the object velocity of the object at each time interval. Depending on the shape of the graph, conclusions can be drawn regarding the object's motion.

So how do you interpret the shape of a velocity-time graph? For this activity, YOU will be the object in motion. You will use a motion sensor to measure your position as you move in a straight line at different speeds.

The Question:

What is the relationship between the motion of an object – YOU – and a graph of velocity and time for your motion?

Variables:

Identify the type of data you will collect to support your hypothesis and state the manipulated, responding and controlled variables in this investigation.

Materials:

• motion sensor
• USB Link
• base and support rod

Procedure:

Step 1:

Step 2:

Upon opening the DataStudio file, you will be presented with a velocity-time graph that looks something like this:

The red line on the graph represents data that has already been entered. Note that the graph begins at zero m/s, so you should be standing still in front of the sensor when the trial begins.

Step 3:

Mount the motion sensor on a support rod so that it is aimed at your midsection when you are standing in front of the sensor. Clear the area behind you so that you can move at least 2 meters away from the motion sensor:

Position the computer monitor so you can see the screen while you move away from the motion sensor.

Step 4:

Before you begin moving in front of the sensor and collecting data, study the velocity versus time graph in order to determine the following:

• Which direction (positive or negative) should you go at the beginning?
• What is the maximum speed (positive or negative) you must achieve?
• How long should your motion last?

When you are ready, stand in front of the motion sensor. Have a classmate start data recording by pressing the "start" button. Data recording will begin almost immediately.

Watch the plot of your motion on the graph and try to move so the plot of your motion matches the velocity versus time plot already there.

Step 6:

Repeat the data recording process a second and a third time. Try to improve the match between the plot of your motion and the plot already on the graph.

Analyzing and Interpreting:

1.	Note the shape of the graph of your motion. What is the description of this motion? (Example: "Constant speed for 2 seconds followed by no motion for 3 seconds, etc.")
2.	What sections of the graph were indicative of acceleration away from the sensor (what did the line on the graph look like)? How would you describe the acceleration in these sections to differentiate them from other sections where you were accelerating toward the sensor?
3.	What would be the physical meaning of a steeper slope on the graph?

Forming Conclusions:

Based on the data you have collected, write a summary statement for the following question:

4.	What is the relationship between the motion of an object – YOU – and a graph of velocity and time for your motion?

Extending:

• Consider repeating this experiment, but instead of trying to match pre-made data, try to match the graph of motion made by a classmate. Take turns trying to match each other's motion! Once you done so, answer Analyzing and Interpreting question #1 as it applies to the graphs of your motion.