- #1
dl447342
- 28
- 5
- Homework Statement
- Find the angular and linear accelerations of the ruler in the diagram below.
- Relevant Equations
- Torque = moment of inertia * angular acceleration = lever arm of force * force magnitude.
Thanks for offering that hint. I said gravitational force is one, and I think it acts about the center of mass. But what about the others? That's the whole point of asking my question.haruspex said:When released, what forces act on the ruler and where?
What are their torques about mass centre?
What are those other forces?dl447342 said:But what about the others?
If gravity were truly the only force acting on the ruler, it would be in free fall towards the center of the Earth, no?dl447342 said:After the system is released from rest, isn't the only force the gravitational force about the center of mass?
Yes. Where is that force exerted?dl447342 said:Well of course there's the normal force exerted by the pivot
You're assuming that there is a torque. What are you basing that on? You said in the OP that you "think" there is a torque; what makes you think that?dl447342 said:but what force creates the torque?
I'm assuming there is a torque because that seems to be implied by the question. If there is no torque, then since the angular velocity was initially zero, it should remain that way; that is, the ruler should remain at rest and not rotate.PeterDonis said:Yes. Where is that force exerted?You're assuming that there is a torque. What are you basing that on? You said in the OP that you "think" there is a torque; what makes you think that?
As @hutchphd has pointed out, this is a very bad way to try to answer physics questions.dl447342 said:I'm assuming there is a torque because that seems to be implied by the question.
Yes, that's correct. So is there a torque, or isn't there? Don't try to guess what you think whoever wrote the question is trying to imply. Just think about the physics. All of the necessary physics has already been stated in this thread.dl447342 said:If there is no torque, then since the angular velocity was initially zero, it should remain that way; that is, the ruler should remain at rest and not rotate.
Torque about pivot on ruler is a measure of the force that causes an object to rotate around a fixed point, known as the pivot, on a ruler. It is also known as moment of force.
Torque about pivot on ruler is calculated by multiplying the force applied to the object by the distance between the pivot and the point where the force is applied. The unit of torque is Newton-meters (Nm) or foot-pounds (ft-lb).
Torque and force are directly proportional to each other. This means that the greater the force applied to an object, the greater the torque and the greater the distance between the pivot and the point of force, the greater the torque.
The position of the pivot affects the torque about pivot on ruler as it determines the lever arm, which is the distance between the pivot and the point where the force is applied. The longer the lever arm, the greater the torque.
Torque about pivot on ruler is used in many everyday objects, such as wrenches, door handles, and seesaws. It is also used in more complex machines, such as car engines and bicycles, to create rotational motion and perform work.