If I consider a man sitting on an office chair that reclines backwards iff you lean backwards.

What could be done to prevent hin from falling? a) raising his legs till they are parallel to ground. b) bring the feet closer to himself(as close as possible) and press them down on the ground.

Please don't suggest any other way. I want to compare these two. Ie, which is better.

Argument in favor of a)

The center of mass moves away from the rear end of the chair towards the forward end of the chair so torque of weight will restore the chair. (This works if you are in an armchair, and are rocking to and fro). However, intuition says contrary to this. I feel scared of falling If I do this.

Argument in favour of b)

Intuition favours this. Normally when we talk about balancing our body, what "feels right" is better for the safety. So, I can not say what is right. Please explain what your views are in this case. Again, the purpose of this question is not to ask what should be done, only what is better to do out of these two choices.

  • $\begingroup$ why is this being voted to close? $\endgroup$ – Saurabh Raje Jun 28 '14 at 8:58

This sounds to me like an experimental question (but be careful not to hurt yourself!).

Note that since you want the chair to rotate forwards towards the ground, you'll want to consider the direction of the angular momentum your motion introduces. If you kick your legs out rapidly, not only does the weight of your feet tilt the chair forward, but the angular momentum of your legs moving upwards in front of the chair will tend to be balanced by an upward motion of the back of the chair. However, if you're tilted too far backwards before you kick out your legs, you'll get a second and opposite angular momentum kick once your knees are straight, which might send you over backwards.

This is why the best approach is to stick out your legs and pinwheel your arms.

  • $\begingroup$ Ok, is it still true if the legs are moved slowly? $\endgroup$ – Saurabh Raje Jun 28 '14 at 1:00
  • $\begingroup$ Then there is less angular momentum. $\endgroup$ – rob Jun 28 '14 at 3:33
  • $\begingroup$ shouldnt we consider the torque of weight $\endgroup$ – Saurabh Raje Jun 28 '14 at 9:00
  • $\begingroup$ Clearly the torque of the weight and the location of the center of gravity are the main effects, and the angular momentum of kicking legs / pinwheeling arms is a second-order consideration. $\endgroup$ – rob Jun 28 '14 at 14:40

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