# Calculating Net Torque on a Circle with Multiple Forces

• physicsCU
In summary, the conversation was discussing how to calculate net torque for a circle with multiple forces applied. The unit of torque was determined to be N*m or Joules, and the concept of torque being measured in units of Joules was discussed. The final conclusion was that torque is not energy and should always be written in N*m instead of J.

#### physicsCU

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I have -0.94, provided the z axis points outward the computer screen.

By the way, what is the unit of torque?

$$\vec{\tau} = \vec{r}\times \vec{F}$$

So it's N*m = J !

I realize that the N*m of torque is not the same kind of N*m as that the one involved in work, for exemple. The first speaks of Force exerted AT a distance, the second of a force exerted ON a distance. But the units remain N*m, and that's Joules! I'm thrown down my chair.

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Torque is in N*m

But N*m is Joules. Don't you find that strange? I find that troubling. :grumpy:

I simply calculated all the torques and added them together:

-.10*30 + .5*30*sin(45°) + .5*20

I have accepted it, no worries.

But what about that force that is off the circle in the third quadrant? Do you ignore that, or what?

That last vector isn't doing any work to turn the circle, so its got no effect. Remember Torque is a cross prodcut between Force and Radius, the force is parallel to the radius, in which case sin(0)=0 and the vector applies no torque.

Quasar makes an interesting point however--- the concept of torque being measured in units of Nm ---> Joules? Energy?

It's best to keep your units of moments around a point in Nm, just as when one calculates the complex power for ckt elements under an sinusoidal steady state voltage or current... the real power (avg power) is measured in Watts, whereas the imaginary reactive power stays as VA (volt amps), rather than watts.

I read an article about that. I don't remember what the explanation was, but they said it made sense.

you might be correct.

Anyway just to clarify, Torque is the turning effect, although it has the same units as Joules it's not energy, so it msut never be written in J, but N m.

## 1. How is net torque calculated on a circle with multiple forces?

The net torque on a circle with multiple forces is calculated by multiplying the magnitude of each force by its lever arm (distance from the center of the circle) and finding the sum of these individual torques. This can be represented by the equation T = F x r, where T is the net torque, F is the force, and r is the lever arm.

## 2. What is the direction of net torque on a circle with multiple forces?

The direction of net torque on a circle with multiple forces can be determined by using the right-hand rule. If the forces are clockwise, the torque will be in the direction of your fingers curling towards the center of the circle. If the forces are counterclockwise, the torque will be in the direction of your fingers curling away from the center of the circle.

## 3. Can the net torque on a circle be zero with multiple forces?

Yes, it is possible for the net torque on a circle with multiple forces to be zero. This can happen if the clockwise and counterclockwise torques balance each other out, or if the forces are applied at equal distances from the center of the circle.

## 4. How does the angle of application affect the net torque on a circle with multiple forces?

The angle of application can affect the net torque on a circle with multiple forces. If the forces are applied at an angle to the radius of the circle, the lever arm will be shorter and the torque will be smaller. If the forces are applied perpendicular to the radius, the lever arm will be longer and the torque will be greater.

## 5. Is the net torque on a circle affected by the number of forces acting on it?

Yes, the net torque on a circle can be affected by the number of forces acting on it. If the forces are all acting in the same direction, the net torque will be larger. If the forces are acting in opposite directions, the net torque will be smaller or even zero if they are equal in magnitude.