Torque, force and rotational acceleration

AI Thread Summary
When moving a mass from distance d to 2d on a massless ruler, the force required to maintain stability depends on the rotational inertia. The initial confusion arises from the relationship between torque and distance, where torque is calculated as the product of distance and force. While the force due to gravity remains constant, the rotational inertia increases with the square of the distance, leading to a requirement for quadrupling the force to maintain stability. The discussion highlights the distinction between static and dynamic scenarios, suggesting different calculations may apply based on the system's state. Understanding these principles clarifies the mechanics involved in maintaining equilibrium with changing distances.
The_Journey
Messages
19
Reaction score
0
This isn't a homework question.

I'm really confused at this, say you're holding a massless ruler / stick and there is a mass (m) on it at a distance d from your hand. If you move the mass to 2d from your hand, would you have to apply twice the force as before, or quadruple to keep it stable?

I know torque = r cross F. F is constant (mg), so the force you would have to apply should be twice if you move it to 2d. But my teacher said it is quadruple because the rotational inertia of the stick would be m(2d)^2 which is 4 times the rotational inertia as before.

Can anybody explain to me if the force would have to be twice or 4 times as before?

Again NOT a homework problem, I just thought of this.

Some equations and math would be nice too.
 
Physics news on Phys.org
Nvm I'll just put this in the homework section.
 
NVM...you have two different situations, one static, one dynamic, hence two different answers...if you know the formula for rotational inertia you can work out that result using
v = wr
 
Naty1 said:
NVM...you have two different situations, one static, one dynamic, hence two different answers...if you know the formula for rotational inertia you can work out that result using
v = wr

Can you explain what you mean by static and dynamic? The stick is always stable.
 

Thread 'Is calling fictitious forces "not real" just about terminology?'

Hi there, im studying nanoscience at the university in Basel. Today I looked at the topic of intertial and non-inertial reference frames and the existence of fictitious forces. I understand that you call forces real in physics if they appear in interplay. Meaning that a force is real when there is the "actio" partner to the "reactio" partner. If this condition is not satisfied the force is not real. I also understand that if you specifically look at non-inertial reference frames you can...
View full post »

Thread 'Inclined treadmills and Galilean Invariance'

This has been discussed many times on PF, and will likely come up again, so the video might come handy. Previous threads: https://www.physicsforums.com/threads/is-a-treadmill-incline-just-a-marketing-gimmick.937725/ https://www.physicsforums.com/threads/work-done-running-on-an-inclined-treadmill.927825/ https://www.physicsforums.com/threads/how-do-we-calculate-the-energy-we-used-to-do-something.1052162/
View full post »

Thread 'Derivation of Hamilton's Principle: Questions'

I have recently been really interested in the derivation of Hamiltons Principle. On my research I found that with the term ##m \cdot \frac{d}{dt} (\frac{dr}{dt} \cdot \delta r) = 0## (1) one may derivate ##\delta \int (T - V) dt = 0## (2). The derivation itself I understood quiet good, but what I don't understand is where the equation (1) came from, because in my research it was just given and not derived from anywhere. Does anybody know where (1) comes from or why from it the...
View full post »

Similar threads

I Effects of External Torques on the Angular Momentum of Asymmetric Bodies
Replies
3
Views
2K
B The physics of flywheel launchers (like tennis ball shooters)
2
Replies
60
Views
4K
I Why does a free rigid body rotate only about its COM when F(ext) is applied?
Replies
7
Views
2K
Torque and Moment of Inertia of a Lever Arm
Replies
2
Views
3K
I Does a rotating accelerometer moving linearly measure linear velocity?
Replies
47
Views
4K
Moment of inertia where mass and torque are at a different positions
2
Replies
69
Views
5K
About torque and moment of inertia
Replies
30
Views
7K
B Non-physicist needs your help torquing a nut!
Replies
9
Views
1K
Wheel moving in rotation and translation
Replies
15
Views
2K
I Is it possible to create linear acceleration using nothing but different moments of inertia beteen a wheel and axle?
Replies
5
Views
1K

Hot Threads

Recent Insights

Back
Top