Moment of force ? some clarifications needed.

In summary, the book states that the line of action of a force is a line that passes through the point of application of the force and is perpendicular to the force. The direction of the turning tendency of the force is indicated by an arrow that points in the anticlockwise direction.
  • #1
logearav
338
0

Homework Statement



Regarding the moment of force, this is the definition given in the book
The tendency of rotation is called turning effect of a force or moment of the force about the given axis. The magnitude of the moment of force F about a point is defined as the product of the magnitude of force and the perpendicular distance of the point from the line of action of the force

Homework Equations



Please refer my attachment ( fig 1) which has been given in the book to illustrate this example.
Now my doubts are 1) is PO line of action of force?
2) what that arrow pointing in the anticlockwise direction represent?
Thanks in advance, revered members.

The Attempt at a Solution


 

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  • #2
logearav said:
Now my doubts are 1) is PO line of action of force?
No. The 'line of action' of the force is a line parallel with the force and passing through the point of application.
2) what that arrow pointing in the anticlockwise direction represent?
The direction in which that force would cause the object to rotate. Torque, at least in these simple situations, can be clockwise or counterclockwise. In this case it's counterclockwise.
 
  • #3
is it PF then? pls help because i could not understand the concept of line of action of force
 
  • #4
logearav said:
is it PF then? pls help because i could not understand the concept of line of action of force
"F" stands for the force vector, not a point. The line AP extended is the line of action of the force.
 
  • #5
Thanks a lot sir. But its been mentioned " perpendicular distance of the point from the line of the action of force"
Here the point is P and the line AP is line of action of force. Then How OA qualifies as perpendicular distance, because OA is perpendicular distance to A from the axis of rotation.
 
  • #6
logearav said:
But its been mentioned " perpendicular distance of the point from the line of the action of force"
"The point" is the point about which you are finding the moment of some force.
Here the point is P and the line AP is line of action of force.
No. P is the point of application of the force; the point about which you are computing the moment is point O, not P.
 
  • #7
The arrow for F (extended both ways to infinity) is the line of action of force F. I can't see any right angles marked in, but it looks like OP is not the perpendicular distance to O. Maybe it's OA that is the perpendicular distance from 0 to the line of action of F? You need to mark it clearly. So the moment of F about O is OA * F and the turning tendency is approximately anticlockwise. (Providing I'm correct that F is almost parallel to the y-axis marked "AXIS", is it?)

I wouldn't refer to an axis of rotation, since nothing is rotating (that I know of). I'd rather see a circular arrow drawn about 0, rather than stuck in mid-air near the end of F, to indicate the direction of the turning tendency of the force F about point O.

If F were to cause rotation about 0, then the axis of rotation would be out of the page directly towards you, i.e., perpendicular to the page. *

* Your hand-sketched diagram is not clear; I may be interpreting it differently to how it should be. I'm saying F is almost parallel to AXIS, but it could be viewed as being almost perpendicular to it, too. Only you know what it should be. :confused:
 
Last edited:
  • #8
Thanks a lot Nascent Oxygen and Doc Al for your detailed explanations
 

What is moment of force?

Moment of force, also known as torque, is a measure of the tendency of a force to cause an object to rotate about an axis or pivot point. It is a vector quantity, meaning it has both magnitude and direction.

What is the formula for calculating moment of force?

The formula for calculating moment of force is M = F x d x sinθ, where M is the moment of force, F is the applied force, d is the perpendicular distance from the pivot point to the line of action of the force, and θ is the angle between the force and the lever arm.

How does moment of force differ from force?

Force is a push or pull applied to an object, while moment of force is a measure of the rotational effect of a force. They are related, as a force can cause an object to rotate and thus create a moment of force.

What factors affect moment of force?

The magnitude of the applied force, the distance from the pivot point to the line of action of the force, and the angle between the force and the lever arm all affect the moment of force. Additionally, the direction of the force also plays a role in determining the direction of the moment of force.

Why is it important to understand moment of force in physics and engineering?

Moment of force is crucial in understanding how objects rotate and move in response to applied forces. It is essential in designing structures and machines, as well as in analyzing the stability and safety of structures. It also has applications in fields such as biomechanics and robotics.

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