Hi. I'm Fran.
This is our Go Direct Motion Detector.
The Go Direct Motion Detector works using ultrasound.
The sensor sends out pulses of ultrasound, which echo off the closest object,
and that echo is detected by the motion detector.
The ultrasound is not straight, laser-like in nature.
Instead, it comes out of the motion detector, kind of, in a cone shape that's,
sort of , three-dimensional.
So when you set it up, you want to make sure that you don't have
objects that are going to be in the way of that cone and generate echoes that are not
echoes of the object you're trying to measure.
One of the most common activities that people do with this is they measure people
walking towards and away from the motion detector.
So let's give that a try.
First, I need to turn it on by pressing the power button.
And then the blinking red light indicates that is ready to connect.
I'm going to need the ID number on the label to find the motion detector that I
want to connect to on my list in Graphical Analysis.
So let's see.
Looks like there is… Once I connect, I'm ready to take some measurements.
So I'm going to go ahead and move away from and then towards the motion detector.
All right. So there's my graph.
It's pretty good, and there's kind of a glitch at the beginning.
And one way to improve what you see on a position-versus-time graph with the motion
detector is to use some sort of large, flat object to reflect
the ultrasound back.
So I've got a piece of foamcore, which I'm going to use to reflect the
ultrasound back at the motion detector.
And you can already see, that gives me a
much nicer, smoother graph.
Another common use for the motion detector is to use it with a cart on a track.
So let's set that up as well.
First, I'm going to put the motion detector on my motion detector bracket,
which comes with the cart and track system.
And then I'm just going to slide it into the top groove on the track.
The other thing I have to do is change the channel.
While the default Motion channel is very good for most activities that you would do
with the motion detector, we're actually going to use the Motion
cart channel for cart on a track.
So I'm going to start a new experiment.
Graphical Analysis will reconnect to the same motion detector,
but I'm going to take the opportunity to use the Sensor menu down in the bottom
right and change that channel from the Motion channel to Motion cart.
Changing the channel to Motion cart actually changes the response
of the motion detector.
So it is less likely to see extraneous echoes when dealing with the small cart.
In addition, I've added magnet tabs to this cart, so I can attach the
motion detector flag.
And that also provides an additional surface for the ultrasound
to bounce off of.
I'd like to have this cart go up and down the track, but as we saw from the
first experiment, if the cart is moving towards the motion detector,
just like when I was moving towards the motion detector, that's actually going
to give me a graph that goes downward.
I'd like that graph, for position versus time to go upward,
so it'll give me a positive velocity.
So I'm going to do two things.
First, I'm going to bring this down to the lower end of the track and Zero the
sensor there.
And the second thing I'm going to do is reverse the direction
of the motion detector.
Now, I'm ready to collect data.
I'm looking for motion of a cart up and down a ramp.
And there it is.
With graphs like this, it's often very instructive to look at the
velocity and acceleration graphs as well.
So as the position data is collected, the Graphical Analysis software
automatically creates calculated columns for velocity and acceleration,
which can then be graph versus time.
I simply changed the view to two or three graphs, in this case, three,
in order to see those extra graphs.
What I'd like to do is compare the slope of the velocity graph,
which I can find by doing a curve fit on my velocity graph to the average
acceleration that was calculated.
So I'm just going to select my acceleration graph, and this time,
I'm going to choose View Statistics.
The statistics show that the average is - 0.526, whereas the slope of my
velocity-versus-time graph is -0.527.
Hmm… Pretty good agreement there.
Excellent data.
The Go Direct Motion Detector can be used in any of the motion detector experiments
in our experiment manuals.
You can find these on our website.