In this two-part lesson students investigate acceleration and combinations of signature motions using an accelerometer. They explore more complex motions and how to represent and compare them. This lesson also introduces students to vectors.
Their goals are as follows:
This article (Cork Accelerometer) explains how the accelerometer works and describes how to construct it. Note that I fill mine with vegetable oil instead of water.
I begin this lesson by going over the goals. The focus is on understanding the meaning of acceleration (speeding up, slowing down, or changing direction) and gaining a sense of the amount of acceleration involved in different motions.
To do this students will use a simple tool, the accelerometer. These are very easy to construct. However, you do need to gather some materials ahead of time in preparation. Refer back to the Getting Started section of this lesson for a detailed list of materials and instructions on building the accelerometers.
I begin by asking my students how they can tell if an object is accelerating. Give them the following scenario:
“Imagine that you are sitting in the back of a bus you cannot see out the windows nor can you hear the engine. How would you know if the bus was accelerating or going at a constant velocity?”
Give students time to think and chat with their neighbors. as they are talking I circulate around the room listening in on conversations for a few minutes then call on students to give their ideas. I facilitate a discussion with the entire class asking for people's ideas to responses until we get more of a clear understanding as a class where are ideas are
Begin by showing students the accelerometer. Explain to them how the accelerometer works and what its component parts are.
A note about safety: Be sure to let students know to handle these carefully as I have had accidents where students have dropped them or unscrewed the lid resulting in oil spilling all over lab table or on the floor. I've had my accelerometers for around seven years, so the oil in them is fairly rancid at this point. Trust me, you do not want this spill to occur in the lab.
Explain the question they are investigating: How does the accelerometer indicate changes in velocity?
You want to introduce the language for this unit in context, as the learning experiences roll out. So far the terms speed and acceleration have come up, and now velocity is added. I add these words to our word wall and help my students to define them. Velocity is speed in a given direction, acceleration is change in velocity or change in speed in a given direction, and speed is the rate of change in position.
Using the accelerometers, students should explore how the accelerometer indicates a change in velocity (for example, speeding up, slowing down, or change in direction) causing the cork to move. They will observe that the cork always leans in the direction of acceleration. The more it leans, the greater the acceleration.
Have them explore what happens when they move the accelerometer in various ways. They should turn the jar upside down so that the lid is on the table. Demonstrate this by sliding the accelerometer across the surface (start, stop, speed up, slow down, crash, move back and forth, and start-stop-start-stop).
Model how to record their observations in their journals. Draw the image of a cork on a string and how to record its change in position.
They should explore around 10 motions and record each, including the four signature motions (speeding up, slowing down, constant, and crashing). If students are struggling for ideas for the 10 motions let them know they can do fast acceleration, slow acceleration, fast constant, slow constant, etc.
In this part of the lesson students explore the accelerometer while its attached to the cart. Begin by showing students an image of a complex motion story with the accelerometer image added to the various components of the story.
Ask students to predict two different scenarios. For the first scenario, the cart always moves left to right, but starts then stops and starts and stops. Have them draw this prediction graph on an individual whiteboard or in their journal and then share their ideas to the class.
For the second scenario the cart starts slowly then stops quickly, reverses direction, and slowly speeds up to a constant speed right to left, then coasts to a stop.
Once they have predicted both scenarios, they should observe these scenarios with the accelerometer and carts. Have them record their observations in their journal noting any patterns they see and what they notice about using the accelerometer.
To get more practice interpreting complex motions with the accelerometer, return to the graphs of Complex Motion Stories they drew in an earlier lesson. For each, label the sections of the graphs with the signature motion they represent, predict how the accelerometer would behave during the motion, and label the sections of the graph with the accelerometer reading you predict will happen. Then act out the motions with the accelerometer. Compare their observations with their predictions.
This lesson is a great application of Science Practices 2 and 4 which I highlight in the video below: