Getting Started with Motion
Use the accelerometers to investigate movement.
1. Open the Accelerometer X by finding the X icon in the sensor drawer and press to open.
2. Place the phone flat on a table or level surface. Put the phone in graph mode. Try the following experiments, repeating each motion a few times while you watch the graph.
Slide the phone to the left and right.
Slide the phone toward and away from you.
Lift the phone straight up off the table and then place it back down.
For which motion do you get the highest value?
3. Touch the Y icon to open the Accelerometer Y card. Repeat the motions in Step 2. Which motion gave you the highest value?
4. Touch the Z icon to open the Accelerometer Z card. Again, repeat the motions in Step 2. Which motion gave you the highest value? What do you notice?
5. Experiment with using multiple sensors at once, repeating the motions from Step 2. What do you notice when you view Accelerometer X versus Accelerometer Y? Accelerometer X versus Y and Z?
6. Continue to explore by experimenting with moving your phone in different ways. Place the phone flat on a table and drum on or shake the table. Drop the phone, from a safe distance, into your hand or into something soft. Place the phone inside a long sock and swing it around your head. Which accelerometer worked best for recording your motions?
What’s Going On?
Objects have a tendency to stay put, or to keep moving if they’re moving—we call this tendency inertia. Newton’s First Law expresses this idea formally: An object continues in its state of motion or rest unless acted on by an unbalanced force.
When an unbalanced force does cause an object to budge, we say the object accelerates: its velocity, or speed, changes—either by speeding up, slowing down, or changing direction. Acceleration is measured as a change of velocity (meters per second) in time, or meters per second squared (m/s2).
Your phone has a device to measure these changes in motion—an accelerometer. Inside an accelerometer, small suspended masses are free to move. Changes in motion cause these masses to shift, much as your own head tends to flop forward when you’re in a car that stops suddenly. Measuring these subtle inertial shifts, an accelerometer in a phone can detect changes in motion and orientation, useful for switching the screen from landscape to portrait mode, for playing games on your phone, and more.
You probably noticed a persistent acceleration in the Z axis, even with the phone sitting still on a table. This is the acceleration we experience here at the Earth’s surface due to the pull of gravity, approximately 9.8 m/s2.
Use the accelerometers to study your motions throughout the day. How do the sensor cards or graphs change as you walk up and down stairs, skip, swing on a swing set, play soccer, or ride the bus? Compare with a friend.
Experiment by attaching your phone to various other moving things—a skateboard, a bicycle, your dog. What patterns of acceleration can you detect?
Take your accelerometer tool to an amusement park. Some roller coasters put your body through accelerations of up to 3 or 4 gs, that is, three or four times the normal acceleration due to gravity. How many gs do you (and your phone) experience on your favorite ride?