In this activity, you will explore the built-in accelerometers in a cell phone to sense changes in speed by utilizing Google’s Science Journal app. Grades: 8. Duration: 30 – 45 minutes.
What Factors Make a Car Faster or Slower?
The force generated from a car’s engine can propel the vehicle along any plane, but what about a toy car with no engine? What other factors affect its acceleration? A car (or any object) in motion, tends to stay in motion. But when that car is still, it has a tendency to stay still. This tendency to stay in its current state is called inertia and is Newton’s first law of motion: An object continues in its state of motion or rest unless acted upon by an unbalanced force.
Acceleration is what happens when the above “unbalanced force” is introduced. When you say a car is accelerating, that means its speed is changing. It can go faster, slower, or change direction. You can measure a car’s acceleration based on how many meters it moves per second squared (m/s2).
Can You Control a Toy Car’s Acceleration?
What can you do to control a toy car’s acceleration? For this exploration, let’s see how the surface of the plane the car travels on, and the angle of that plane, affect its acceleration. We’ll be able to see how far the toy car goes, but we can also directly measure its acceleration.
The Google Science Journal app uses the built-in accelerometers in a cell phone to sense changes in speed. This allows the phone to switch its display mode between portrait and landscape depending on how the phone is held.
Open the Google Science Journal app on your device. Your screen should look like this:
The blue area tells you which sensors data is being displayed, and lists all the sensors available to you including light, sound, X, Y and Z acceleration, and barometric pressure. If you do not see available sensors listed, just click on the arrow circled in red on the left (see image below). The active sensor currently displaying data will have a yellow line underneath it:
It’s interesting to note that when using the Google Science Journal app to measure acceleration on the Z axis, you will notice a persistent fluctuation even when the phone is completely still on a stationary surface.
This is due to the acceleration created by the gravitational force of the Earth which is approximately 9.8 m/s2.
Create Your Own Test Course
Gather the following materials:
- 1 long strip of cardboard (at least 24 inches in length)
- 1 toy car
- Felt or carpet fabric (enough to cover one side of the cardboard)
- Sandpaper (enough to cover one side of the cardboard)
- Tape (enough to tape the sandpaper to the cardboard)
- 2 paper binders (to clamp the felt to the cardboard)
- 10 cups
- 1 protractor
- 1 cell phone (or tablet) with the Google Science Journal app installed
Tape sandpaper to one side of your cardboard strip. Try to cover as much surface area as possible. This will serve as one side of the ramp that the toy car will roll down.
Traditionally, vehicle acceleration is tested on drag strips. These are straight tracks usually a ¼ mile long. Using standard sized 81/2” x 11” copy paper, you’ll need to tape together at least eight pieces.
Place a distance marker every inch along your drag strip so that you can later measure how far the car travels under various conditions.
Rest one end of your cardboard on two cups and lay out your paper drag strip in front of the opposite end of your cardboard.
Your entire setup should look similar to the one in the picture below.
Next, measure the angle of the cardboard from the base, where it meets the drag strip. Make sure to write down all your observations. So far, this includes the number of cups used and the angle of the cardboard.
You’re almost ready to run your first trial, but first, you will need to attach your device to your toy car. How you do this will depend on your device as well as your car’s shape and size. See the image below for a sample.
Now it’s time to run your first trial. Press the “record” button located on the bottom of the Google Science Journal app interface (see image below). Point the car towards the drag strip and let it roll. When your car stops rolling, note how many inches it has rolled, stop the recording, and note the maximum acceleration.
If you prefer to see your acceleration results in graph form, just click on the graph icon.
You can also record in this graph mode:
Your notes should now include the type of surface used for this trial, the angle of the cardboard, number of cups used, and the maximum acceleration/distance traveled by the toy car. You’ll find the provided graph conveniently accommodates documenting these results.
Now that you have documented your first trial, you can change one variable and run a second trial. What are your variables? Which ones will you change? The variables that are directly under your control are:
- Type of surface (cardboard, sandpaper or felt) to increase or decrease friction.
- Number of cups used to increase or decrease the height or angle of the cardboard ramp.
For your second trial, as well as all following trials, it’s important to change only one variable and keep everything else you do the same. This way you can be sure that the results you observe later are only due to the changes you have made.
Do you think the toy car will accelerate faster on the felt, cardboard or sandpaper surface? What about the angle of the cardboard? Does a greater angle = greater acceleration? Make a prediction before you continue to see if you are right. Continue running trials.
Results – What Happened?
Did you try all surfaces? Did you try at least two different angles? Under which conditions did the toy car travel the farthest? Which conditions lead to the most acceleration? You may have noticed that the different surfaces had different effects on the toy car’s acceleration. These different surfaces introduced varying amounts of force into the equation depending on the type of surface. The force created by these surfaces runs against the acceleration, thereby causing a decrease in acceleration. Were you able to determine which surface slowed the car down the most? Now that you know the results, do you think you can control how far/fast the toy car goes?
Ready for an Extra Challenge?
Challenge 1: You may find it easy to get the car to go very far, or even slow it down enough that it barely travels past the ramp, but can you control just how much it travels? Get the toy car to go 46 inches down the paper drag strip. (Anything above or below this amount does not count. Strategy and control are very important to accomplish this challenge.)
Challenge 2: Spoiler Alert! The highest angle (though under 90 degrees) you place the ramp in while using the smoothest surface will give you the greatest acceleration. But can you control the conditions enough to reach a target acceleration? Reach a peak acceleration of 18 m/s2 manipulating only ramp angle and surface type.
More on Motion
We hope you have enjoyed exploring Newton’s first law of motion through your acceleration experiments. If you are inspired to learn more, then you are in luck! Whether you want to continue exploring acceleration through making a bobsled or are interested in learning about the forces of flight through creating a human-powered flying machine, there are more hands-on activities for you to explore on our learnXdesign website.
0 – 60 mph: An Exploration of Acceleration activity is made possible with support from Making & Science, an initiative of Google.