Will this stick spin if it has no pivot?

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In summary, the conversation discusses a scenario where a one-dimensional rod is struck at one end, causing it to move translationally. The question arises whether it will also spin, and the possibility of this is explored using the concept of torque. It is concluded that the rod will indeed spin as it moves off.
  • #1
Albertgauss
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Hi all,

Here is what I am trying to understand qualitatively. It is NOT a homework problem:

A long, one-dimensional rod of mass M and length L is in free space. There is no gravity, no forces, and no pivot. Its just a rod sitting there, floating, with nothing else around. Let's say its L=0 end is at the origin (y=0), and its L=L end at a positive y=L. Suppose I strike the y=L end of the stick in the +X direction. By Newton's Inertial Law, the stick should move translationally as I transferred momentum to it. But will it spin? I can't figure that out.

I thought perhaps that it might. I tried to think of the stick as comprised of many atoms attached to each other by springs. I made some simplifying assumptions. The atoms at the y=L of the stick that receive the WHACK will experience a force via an impulse in the pure positive X direction as long as I am in contact (however brief) with the y=L end. The atoms at the y=L end will also experience a restoring force due to their neighboring atoms trying to pull them back. That restoring force would point towards the third quadrant. The restoring force and my impulse force would produce a net force pointing towards the fourth quadrant, and hence I would have a clockwise torque. Thus, I would conclude the rod will indeed spin as it moves off.

How am I doing?
 
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  • #2
It will spin.

The force applied is at a non-zero distance from the centre of mass.
 

FAQ: Will this stick spin if it has no pivot?

1. Will a stick spin if it has no pivot?

Yes, a stick can spin without a pivot if it is given enough force and has a smooth surface to rotate on.

2. How does a stick spin without a pivot?

A stick can spin without a pivot if it is given an initial force or torque, causing it to rotate around its center of mass. The stick's smooth surface also allows it to rotate without friction or resistance.

3. What is a pivot and why is it important for spinning?

A pivot is a point or axis around which an object can rotate. It is important for spinning because it provides a fixed point for the object to rotate around, allowing for controlled and consistent motion.

4. Can a stick spin indefinitely without a pivot?

No, a stick cannot spin indefinitely without a pivot. Eventually, the stick will lose momentum and come to a stop due to friction and other external forces acting upon it.

5. Are there any other factors that may affect a stick's spinning without a pivot?

Yes, other factors such as the stick's shape, weight distribution, and the surface it is rotating on can also affect its spinning without a pivot. For example, a heavier or more asymmetrical stick may be more difficult to spin without a pivot compared to a lighter and symmetrical one.

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