Exploring Acceleration (Part 2)
Objective
Big Idea
Getting Started
In second part of a 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:
- Understand that acceleration means to speed up, slow down, or change direction.
- Gain a relative sense of the amount of acceleration involved in differing motions.
- Learn how to analyze complex motions by finding their component building blocks.
- Begin to think how motion can be represented in terms of vectors.
Materials
- A 16 oz plastic jar with lid
- A small cork with a hole in it
- 20 cm of heavy thread or lightweight string (preferably a dark color)
- 16 ozs of cooking oil or water
- A needle
- Paper towels
- A toothpick or cotton swab
- Overhead transparencies
- Transparency pens
This article (Cork Accelerometer.pdf) explains how the accelerometer works and describes how to construct it. Note that I fill mine with vegetable oil instead of water.
Engage
I administer the following science probe to elicit my students' ideas of the words speed, velocity, and acceleration.
I give them time to think and write then have students turn to their neighbors and talk about their ideas. Once all the tables have had enough time to chat, I bring the class back together and call on table reps to share the group thinking, recording these ideas on chart paper and not correcting any misconceptions as I can revisit their ideas as they complete the investigations and revise the class ideas.
Keeley, Page, and Rand Harrington. Uncovering Student Ideas in Physical Science: 45 New Force and Motion Assessment Probes. Vol. 1. Arlington, VA: NSTA, 2010. pp 55-56
Explore
In order to slow things down so that your students can note the subtle behavior of the cork and string, they will observe videos of the accelerometer. Their focus is on the relationship between the position of the court in the frame and how that relates to the acceleration of the cart.
As they study each video, they use an overhead transparency and marker to record the position of the cork in each frame, creating a film strip of the frames and look for patterns.
They then draw sketches in their journal, noting where the cork is in each frame and what is happening to the accelerometer at that point.
When they have finished collecting data, they sketch a velocity over time graph for each entire video including all the signature motions that they noted in the video, using the accelerometer data to inform the process.
The video below highlights how this lessons uses Science Practice 5: Mathematical and Computational Thinking.
Explain
To wrap up this lesson and tie together worked on previous lessons on graphing students will observe a complex motion video video, then analyze the motion of the cart. Next they generate a strobe picture and draw a sequence of sketches that show the position of the cork in the accelerometer for each frame.
Using the strobe and accelerometer information they create a velocity over time graph of the motion with PowerPoint or other similar software and label each segment of the graph with the signature motion (e.g., speeding up, slowing down) it represents, the direction of acceleration taking place, and what the accelerometer reads.
Once they finish their graphs, they can share them at their table and discuss and discrepancies, similarities and things that puzzled them during the process. I find it helpful to post my own graph and share my interpretation as there are a number of ways to interpret and create a graph for this motion.
The goal is to focus more on the interpretation of data and communication of ideas.
Here is a sample student graph created using Powerpoint.
