# Moments using force and distance.

• weedannycool
In summary, the conversation discusses finding the moment of a 4-kN force applied at point A about point O. Two methods are suggested: breaking the force into its x and y components and algebraically summing the moments, or using the equation M=rFsintheta with the position vector between O and A. The latter method is seen as simpler, but it is important to watch for plus/minus signs.

## Homework Statement

The 4-kN force F is applied at point A. Compute the
moment of F about point 0, expressing it both as a
scalar and as a vector quantity. Determine the coordinates
of the points on the x- and y-axes about which
the moment of F is zero

m=fd

## The Attempt at a Solution

i think that i need to find the distance from F to the origin that is perpendicular. since the moment is always perpendicular to the line of action.

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Yes, I think the easiest way is to break F into its x and y components, then solve for the moment about O by algebraically summing the moments produced by these component forces. Moments can be computed this way (force times perpendicular distance), but that is not the only way. Watch plus/minus signs!

is there a simpler way to do this. i can't get my head round it. thanks

weedannycool said:
is there a simpler way to do this. i can't get my head round it. thanks
You can use M=rFsintheta, where r is the magnitude of the position vector between O and A, F stars as itself, and theta is the included angle in between F and the position vector. I find it easier to break F into its x and y components, and then M_o = F_x(y) + F_y(x)

I agree with your approach to finding the moment of force. To calculate the moment of a force, we need to know the magnitude of the force and the distance from the force to the point where the moment is being calculated. In this case, we are given the magnitude of the force (4 kN) and the point at which it is being applied (point A). To determine the distance from the force to the origin, we can use trigonometry to find the perpendicular distance. Once we have the distance, we can use the equation m=fd to calculate the moment as both a scalar and a vector quantity.

To determine the coordinates of the points on the x- and y-axes where the moment of F is zero, we need to find the points where the distance from the force to the point of calculation is zero. This means that the force must be applied directly on the x- or y-axis. So, the coordinates of the points where the moment of F is zero would be (0, A) for the x-axis and (A, 0) for the y-axis, where A is the distance from the origin to point A.

## 1. What is a moment in terms of physics?

In physics, a moment is a measure of the tendency of a force to cause an object to rotate about a specific point or axis. It is calculated by multiplying the magnitude of the force by the perpendicular distance from the point or axis of rotation.

## 2. How is moment different from force?

Moment and force are related but different concepts. Force is a push or pull applied to an object, while moment is a measure of the rotational effect of that force. Force is a vector quantity, meaning it has both magnitude and direction, while moment is a scalar quantity, only having magnitude.

## 3. What is the equation for calculating moment?

The equation for calculating moment is M = F x d, where M is the moment, F is the force applied, and d is the perpendicular distance from the point or axis of rotation to the line of action of the force.

## 4. How does distance affect the moment of a force?

The farther the distance from the point or axis of rotation to the line of action of the force, the greater the moment will be. This means that the same force applied at a greater distance will have a larger moment than if it were applied at a closer distance.

## 5. What are some real-life examples of moments using force and distance?

Some real-life examples of moments using force and distance include using a wrench to turn a bolt, opening a door by pushing on the handle, using a lever to lift a heavy object, and swinging a baseball bat to hit a ball. All of these actions involve applying a force at a certain distance from a point or axis of rotation, resulting in a moment that causes the desired movement or rotation.