Yahoo Answers is shutting down on May 4th, 2021 (Eastern Time) and beginning April 20th, 2021 (Eastern Time) the Yahoo Answers website will be in read-only mode. There will be no changes to other Yahoo properties or services, or your Yahoo account. You can find more information about the Yahoo Answers shutdown and how to download your data on this help page.
Trending News
In space, can you get a pencil spinning with a single touch?
You're in space, zero gravity, and a pencil is floating in front of you. If you tap the end of the pencil with your finger, my sense is that it should float away from you and also start spinning.
1. Is this right?
2. If this is right - I've learned that producing a moment on an object requires a force couple. Your finger on the pencil is one force; where is the other one coming from? (Do I need to think of the pencil as a chain of mass elements, or something? Would the answer to 1. be different if the pencil were infinitely rigid?)
(Okay - so the other force is the reaction force, and it acts through the pencil's center of mass even though that isn't where your finger touched it?)
2 Answers
- WilvinLv 69 years agoFavorite Answer
I'm pretty sure creating a moment does not require a couple force. It just requires that the net force is not applied directly at through the centroid of the object or in equilibrium negating each other. Creating only a moment without a resultant force or "translational" motion is when a force couple is necessary.
So, I think if you tap the end of a pencil in space and the force vector does not go through the center of mass of the object, it should rotate and translate.
- 9 years ago
The pencil will spin around its center of mass, so there's your other force couple.
Also called CG or Center of Gravity.
Source(s): A report I read on model rocket stability when I was a kid.
