"Linked" objects on separate paths

[rexboggs5]

Some time ago I saw a flipchart that allowed me to move one wee dot along a path (a straight line) and simultaneously another wee dot moved along a different path (a horizontal line).

In particular I want to move a dot around a circle and have the related dot move up and down a line. The purpose is to show the link between uniform circular motion and simple harmonic motion.

So far I can get the 2nd dot to move, but it doesn't stay 'lined up' horizontally with the 1st dot. Which rather defeats the purpose.

Is this possible? If so, how?

I have attached what I have so far.

Cheers

Rex

[Westlake]

Had a go using a different strategy altogether - flipchart attached. Not totally satisfactory for a number of reasons.
You have to keep the pen on the dot, otherwise the accompanying square can shift up or down. I don't really understand WHY that happens as the dot and eraser object are Grouped..
I would have expected that they would simply move together as long as any part of the grouped object was selected.
However: IT DOES WORK!
Looking forward to the solution to this! :confused:
Hilary

[saha]

I had a go at it too but failed.

This has to got to do with the amount of incremental movement along the circle and the straight line. You may be able to get he two points to align horizontally all the time using a lot of trial and error.

The length of your vertical line is 15 cm.
This should translate to a diameter of about 4.8 cm for the circle to keep the path traversed the same for both dots.
Now if both dots did move by same increment and both started at exactly the same point, then you could achieve what you are trying to do.

[saha]

Hi Rex,
Here is an updated flipchart. Hope this help you teach the concept to your students.

Bear in mind this was not made with Activstudio.

First you can click on each individual dot to show the motion independently.
Then you can click the reset button to reset the page.
Then click on the text "Start Simple Harmonic Motion".

You should now see ideal Simple Harmonic Motion.

Reset the Page again to start all over again.

[rexboggs5]

Thanks folks for the replies, and in particular thanks for the flps that folks have submitted.

As Hilary noted, the 'linked dot' follows the mouse's y-coordinate and not the y-coordinate of the red dot on the circle. So for this to work, I had to keep the mouse on the red dot while moving it around the circle. Using a mouse on a monitor, this was really hard to do!

But in class today, using the pen on the ActivBoard, it was easy! I was able to keep the pen on the red dot as I moved it about the circle with uniform motion, and the SHM of the linked dot was spot-on. The students were able to correctly answer questions about velocity and acceleration for different dot positions, so the activity achieved its goal.
Thanks again for the replies - great forum! [clap]

Rex

[cmansell]

Perhaps we could have a function that locks the coordinates of one shape to another individually - just lock the y's for example, so when one object moves, the other does too. This should be aside from the mouse pointer, eh?