Relative Motion


Scene: A person riding in an elevator with glass walls tosses an apple in the air while the elevator is moving. How does the toss look from the point of view of people riding in the elevator? How does it look to someone standing still outside the elevator?
These two pairs of clips (int2 & ext2, and int3 & ext3) show the same throw/series of throws from 2 different cameras. The int files are the views from the camera inside the elvator, while the ext files are the views from the camera across the hotel.

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The int/ext2 pair covers five tosses of the apple, and the two clips are lined up approximately 1-2 frames apart. The ext view allows you to see the motion of the elevator far more clearly then the int view, showing that the first toss occurs at a constant upward velocity, the next 3 while slowing down, and the final toss at about the time the elevator comes to rest (ie, constant 0 velocity).
The int/ext3 pair covers only one toss of the apple, but lined up to less than 1 frame of difference. Because the clip is so short, it may be difficult to see the motion of the elevator clearly even in the ext view, but this toss occurs just as the elevator is beginning to accelerate upwards from rest.

Technical Details

It is possible that pair 3 may be off by one extra frame because of the way the landscape blocked the reference points, but we believe it is correct the way it is.

Recommended Software

Primary Author and Contributors

  • Primary Author: Graham (RIT student)


The files available for download on this page are licensed under a Creative Commons Attribution No-Derivative-Works Non-Commercial 3.0 License. You may distribute these materials to your students or use them for educational purposes in your classes, but other uses may require permission from the author(s).