THE MOTION DETECTOR: A MOTIVATING TEACHING TOOL
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motion clip (DIVX decoder is required, click here to download it)
The ultrasonic motion detector records the distance of an object and,
if it is connected to a computer with a specific graphing program,
the computer can draw a line graph that tells the "story" of
what happens during the time of the motion.
We worked with the whole class, making the graphs visible to everyone
by using a projector and a large screen.
The introductory lesson aimed to introduce the basic concepts about motion, i.e. what the variables involved are, trajectory, speed, frame of reference (I'm moving or I'm still in respect of ....).
First of all, pupils made their own walk along a straight trajectory and analysed it:
- by measuring the distance walked, the time taken for walking along the whole distance, the time taken for walking along single distance fractions
- by calculating the speed
- by making the distance/time graph with Excel.
Then the class had a brief conversation about motion
detectors, recalling the situations where this kind of tools in general
and ultrasonic
detectors in particular are used in the real life (to open doors,
to measure
if a car is exceeding the speed limits, radars which follow the plane
flights, way used by bats to detect obstacles...).
The following step
was the expalation of how it is possible to determinate the position
of an object by means
of
ultrasonic detectors.
Eventually the activity with the detector began.
- Pupils were invited to move freely in front of the motion detector. They just had to do it within a certain distance from the tool, due to its detection range.They soon discovered that how one moves affects the shape of the line that the computer draws.
- Pupils had to guess how to move in front of the motion detector to generate a given graph. In other words they had to decide to move forward, backwards or stay still, to move fast or slow, depending on what kind of line they wanted to make.The comparison between the given line and the graph generated while moving is possible because as one moves, the graph describing his/her motion is generated alongside the already existing graph.
Quite easily they find out that:
- to make the computer draw a horizontal line, the walker should stand still (keep the same distance from the detector); lower the line is, closer to the detector they should stand
- to make the computer draw a steeper line, the walker should speed up
- to make the computer draw a flattening line, the walker should slow down
- to make the computer draw a line that changes direction (from up to down or down to up), the walker should change direction
- to make the computer draw a wavy line, the walker should move back and forth many times
Pupils often interpret a distance–time graph
as being a picture of the movement in a vertical plane, rather than
a relationship between two variables,
in other words they confuse the trajectory with the "story" of
the motion. In order to let they overcome this misconcept, they were
challenged with questions like 'Is it possible to produce a vertical
line?'
After some trails (jumping, moving as fast as they could, moving together......),
they realized for themselves that it is impossible to stand in different
positions at the same time.
The main advantages of this teaching environment are:
- the immediate connection between the physical phenomenon (movement) and its mathematical representation (graph)
- the possibility of trial and improvement
- the opportunity to work toghether, helping and encouraging each other
- the possibility to be direct involved in the experience and to have fun while learning.
This
activity is relevant in the sense of being personally meaningful
and is highly motivating. Pupils have the opportunity to watch each
other, to
share what they have observed and discovered. They are
able to teach themselves: they have
discussions, ask questions, find out the answers together. Pupils
are eager to discover answers for themselves, rather than just get
the
answers from the teacher.
Besides, while they try to understand and
reproduce distance–time
graphs, pupils have the opportunity to develop their
inquire
skills.
They make
observations and predictions, find out relationships between variables,
interpret results...
Teacher: S. Turra
