Physics Stack Exchange is a question and answer site for active researchers, academics and students of physics. Join them; it only takes a minute:

Sign up
Here's how it works:
  1. Anybody can ask a question
  2. Anybody can answer
  3. The best answers are voted up and rise to the top

I wish to find an everyday situation that illustrates the following:

A rod is moving in a direction perpendicular to its axis. One end "gets caught" and the rod starts rotating around this end. THE SPEED OF THE OTHER END OF THE ROD WILL THEN INCREASE BY A FACTOR SQRT(3).

Here is an illustration.

Can someone please think of a simple situation in everyday life that illustrates this transition from translation to rotation. Of course it is not needed to see the increase in speed, but just a situation where you could ask a student what speed the rotating object will have. (Just rods flying through the air is not what you see every day.)

If the situation is free of gravity (moving horizontally), it would be a better illustration, I believe.

(A related situation, but too complex and different is if you sit on the top of a telegraph pole. If the pole breaks at the bottom you will suffer less injury (theoretically) if you jump off the pole immediately rather than going down with it. (Speed less by a factor sqrt(1.5) I believe.))

A pair of ice skaters meeting with speed and taking each others hands and starting to rotate together would resemble the situation a little. But the mass of the skaters is concentrated to their bodies and the only thing accelerating would be their hands if they held them out.

(The classical illustration of a skater making a pirouette by pulling in the arms will not help here, of course.)


share|cite|improve this question
What's wrong with visualizing a rod as you describe? Why do you think it's important to have some so-called "real world" example? If you must, consider a line of figure skaters, perhaps with a stiff rod keeping them parallel, and the skater at one end of the line grabs a fixed post. But I think you do your students a disservice by thinking they can't visualize a rod in space. – Carl Witthoft Jun 18 '14 at 17:01
Falling off a ladder? – John Rennie Jun 18 '14 at 17:23
Aha :-), following up on @JohnRennie's comment: Daredevil jumping into free space, then grabbing a horizontal flagpole or streetlight and swinging around same. – Carl Witthoft Jun 19 '14 at 11:35
Thanks for the comments. I'm still on this track :) I just got multibody simulation running. I now realize the ice skating example is not so good. If the ice skaters grip hands at shoulder height, they may possibly both fall on their behinds, since they grip quite a bit above the bodies Center Of Gravity. And gripping low, at the level of COG, is very hard, large forces involved. 50 cm from center at 2 m/s would mean a force of 8 times body weight!!! Any further suggestions appreciated. (I am sure most people could imagine rods flying in space. I just look for an example from reality.) – ycc_swe Jul 18 at 8:17

Your Answer


By posting your answer, you agree to the privacy policy and terms of service.

Browse other questions tagged or ask your own question.