What they look like

How the sensor works

A Motion Sensor is a sonar device that emits ultrasonic pulses, which reflect off an object.

A datalogging system will process data collected by the motion sensor. The raw data relates to how long it takes for the ultrasonic waves to make the trip from the Motion Sensor to the object and back. Using this time and the value for the speed of sound in air (known), the distance to the nearest object can be determined.

Once distance and time are known, the datalogging software may be used to calculate the speed and acceleration of the object.

Students will be aware of a similar example in nature, where a bat can navigate by sending out waves and "listening" for the echo.
The information is then decoded and processed, in the brain of the bat.

For practical reasons, a motion sensor will send out a wave in a particular direction. This resembles the cone of light from the headlamp of a car. 

As in the case of an echo, the reflector of the sound must be a certain minimum distance away from the source of sound (Motion sensor) for the system to be able to process the data. Normally the object must be at least 40cm away. At long distances, stray objects can become a problem.

Where it can be used

• Walking toward and away from the Sensor
• Graph matching
• Measuring velocity
• Measuring acceleration
• Momentum investigations
• Movement of bodies on a ramp or gliders on an air-track
• A bouncing ball
• Newtons 2nd Law of Motion
• Simple harmonic motion