Science with a smartphone: accelerometer

Key concepts

physics
Move
position
speed
acceleration
Measurement

introduction

Have you ever played a video game with a controller that uses motion controls? Have you ever wondered how a smartphone sometimes seems to “know” if you are moving? How do these electronic devices measure movement? Try this activity to find out!

background

You probably know the units we use to measure distance and speed. In the US, someone could be said to be 5 feet 11 inches tall (measuring distance) or that we are traveling 55 miles per hour on the freeway (measuring speed, which is a unit of distance over a period of time). Scientists use the metric system, which measures distance in meters (m) and speed in meters per second (m / s).

To reach a certain speed, an object often needs to be accelerated or decelerated. You can use the word “accelerate” to describe something that is accelerating (e.g. a car accelerating after a red light) or “slow down” to describe something that is slowing down (e.g. a car that applies the brakes). We can explore these ideas further. While speed measures how quickly the distance changes, acceleration measures how quickly the speed changes. That makes the units of acceleration a bit strange: meters per second per second – or “meters per second squared” (m / s2). When something has a constant speed, e.g. B. a car with cruise control on the highway, its acceleration is zero. If the speed changes at all, the acceleration is not zero. For example, when a car is stopped at a traffic light, it has a speed of 0 m / s.If it accelerates and two seconds later it has a speed of 10 m / s, its acceleration was 5 m / s2. Roller coaster riders can experience accelerations of up to approx. 60 m / s2, and fighter jet pilots can experience accelerations of up to 90 m / s2 for a short time! If this all sounds confusing, don’t worry – you can just imagine speeding up as how fast something is speeding up or slowing down (if it is slowing down, the number is negative).

What does all of this have to do with smartphones and video game controllers? Acceleration can be measured with a small electronic device called an accelerometer. Most smartphones these days have built-in accelerometers and can run apps that display the accelerometer readings. So if you want to explore the movement in the world around you, all you need is a smartphone!

materials

  • Smartphone or tablet with internet access and authorization to download and install an app
  • Soft surface such as a pillow, bed or couch
  • Adult (to check and download the app)
  • Access to a playground (optional)
  • Velcro (or other method) to attach the phone to your arm or leg (optional)
  • Vehicle for driving or retraction, e.g. B. Bicycle, car, bus, etc. (optional)

preparation

  • Have an adult help you find and download an “accelerometer” app on a smartphone or tablet. There are many free options, but some apps may have ads or in-app purchases enabled.
  • Get to know your accelerometer app. Some apps only display a number on the screen while others display a counter or graph. An app that lets you record data and automatically find minimum and maximum values ​​is best for this project.
  • Most accelerometer apps display three acceleration values ​​with labels like “X”, “Y”, and “Z”. These correspond to the movement of your phone in three-dimensional space.
  • Typically, when you lay your phone flat on a table with the screen up, the “X” acceleration is moving from left to right, the “Y” acceleration is moving toward the top or bottom of the device, and “Z “Acceleration would be any movement up and down (above or below the table surface).
  • Some apps may allow you to combine readings from all three directions and show the combined or total acceleration.
  • Make sure the app works: move your phone and you should see the numbers change.

Procedure

  • Measure the acceleration of “typical” movements you make during your day. Hold the phone in your hand or pocket it as you walk around, sit / stand up, go up and down stairs and so on. How big are the accelerations that you are measuring?
  • Now measure the accelerations of “faster” movements. Try jumping, running, twisting, or waving your arms around (don’t drop the phone!). How big are these accelerations?
  • Let the phone fall briefly on a soft surface such as a pillow, bed, or couch. What is the acceleration when the phone hits the ground? Do you think the acceleration would be greater if the phone were dropped from a higher place or landed on a hard surface? (Don’t test this!)
  • How difficult is it to move at a constant speed? Place the phone on a table and try to push it in the X or Y direction. Can you set the corresponding acceleration value to zero?
  • Extra: Tilt the phone without moving it. Do the acceleration values ​​change depending on how you tilt the phone?
  • Extra: Take acceleration measurements in a playground. What happens when you go down a slide, swing on a swing, or climb the climbing poles? Where do you experience the greatest acceleration?
  • extra: Take acceleration measurements in different parts of your body. You can use Velcro (or other tape) to attach the phone to your arm or leg. Which part of your body experiences the greatest acceleration when you run? The smallest?
  • Extra: Take measurements in a vehicle. What are the accelerations when riding a bike (don’t look at the phone while driving!) Or driving in the car or bus?

Observations and results

You should be able to easily measure accelerations up to about 10 m / s2 while making regular movements while holding a phone. Smartphones, fitness trackers, and pedometers can track changes in these accelerations to keep track of how many steps a person takes during the day.

The accelerations can be a bit higher if you put the phone in your pocket instead of holding it because it bounces around more. Faster movements, such as A vibrating phone, for example, can lead to accelerations of more than 50 m / s2 – almost the same accelerations that someone feels when riding a roller coaster. Some electronic devices, such as B. Laptops have a “fall detector” and switch off automatically to avoid damage if they detect excessive acceleration. (Again, don’t test this one!)

You might be confused when you find that the acceleration value can change when you tilt your phone. After all, the phone doesn’t move – its speed is zero. So shouldn’t the acceleration be zero too? This is because accelerometers also sense acceleration due to gravity, which is 9.8 m / s2. When you tilt your phone, the direction of gravity changes relative to the body of the phone. Even when the phone is stationary, the acceleration values ​​for X, Y, and Z differ depending on which is facing down. This is how motion controls work in video games (e.g., tilting the controller to steer in a racing game).

More to discover

Science Buddies accelerometer technical note
Speedy Science: How does acceleration affect distance? by Scientific American
Show Science: Observing Objects in Free Fall by Scientific American
STEM activities for children from Science Buddies

This activity was offered to you in collaboration with Science Buddies

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