What exactly is a Torque?

Answer 1

For equilibrium, the horizontal components of the forces acting on an object must cancel one another, and so must the vertical components. This condition is necessary for equilibrium, but not sufficient. For example, if a person stands a book on a table and pushes the book equally hard with one hand in one direction and with the other hand in the other direction, the book will remain motionless if the person's hands are opposite
each other. (The net result is that the book is being squeezed.) If, however, one hand is near the top of the book and the other hand near the bottom, a torque, or turning force, is produced, and the book will fall on its side. For equilibrium to exist it is also necessary that the sum of the torques about any axis be zero.

A torque, or moment of a force, is the product of the force and the perpendicular distance to an axis of rotation. When a force is applied to a heavy door to open it, the force is exerted perpendicularly to the door and at the greatest distance from the hinges. Thus, a maximum torque is created. If the door were shoved with the same force at a point halfway between handle and hinge, the torque would be only half of its previous magnitude. If the force were applied parallel to the door (that is, edge on), the torque would be zero. For an object to be in equilibrium, the clockwise torques about any axis must be cancelled by the anti-clockwise torques about that axis. It can be proved that if the torques cancel for any particular axis, they cancel for all axes.

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A force applied to a body that causes it to rotate creates torque. Similar to force, torque acts to angularly accelerate a spinning object (in other words, make it spin faster). The equation for torque (expressed as G here, but other textbooks may use t) looks very much like your good ol' F = ma:

G = Ia

Instead of mass, we have rotational inertia. Instead of linear acceleration, we have angular acceleration.

Now, if a force is applied linearly to make an object move, its torque is defined as:

G = F × r

r is defined as the distance from the axis of rotation at which the force was applied. The line from the axis of rotation to the place where the force is applied is called the moment arm. Notice how this is a cross product. So, if the force was acting in line with the moment arm (either 0° or 180°), there would be no torque, and you would be moving the object only translationally.
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Rotational Energy
The work that a rotating body does is also similar to the definition of translational work. Instead of force, we use torque. Instead of displacement, we use angular displacement. Thus:


(Equation 5-12)


And since power is the rate of work, we have:

P = Gw

Note also how similar this is to power for linear motion, P = Fv.

Now, we can also extend the analogy for kinetic energy as well. Remember we used kinetic energy to derive the concept of moment of inertia in the first place? Here is the equation again:


(Equation 5-7)


Now that we have this, let's make an example to put all our knowledge together. We have a hoop, a disk, and a sphere that will roll down a ramp with an angle (q) of 17° as shown on the illustration at right (click on the illustration for a VRML model of the ramp).
Each of them have the same mass and radius and will be released simultneously from rest at the top of a ramp whose length (L) is 1.5 m. How fast are each of the objects moving at the bottom of the ramp?

We can do this using a conservation of energy method. At the top, potential energy is Mgh or MgL sin q for each of them, right? They are not moving or rotating at the top so they don't have any translational or rotational kinetic energy. So, their total energy at the beginning is just MgL sin q.

Now, after they roll down, they will lose all their potential energy but should have both translational and rotational kinetic energy. Therefore, we set the sum of the two of them equal to the energy before they roll:

Answer 2

A Torque, (qualitatively), is the rotating effect or turning effect of a force. That is, a measure of the ability of a force to rotate or turn something, when applied at a particular point.

Mathematically (defining equation) it is a cross product and hence a vector. T = r x F
Here T represents torque, F is the force(vector) and r is the position vector of the force applied with respect to the axis about which the body is made to turn. A diagram is helpful; but I can't draw it because of the limitations of this software.

The direction of the torque is given by the right hand clasp rule for cross products. This direction is perpendicular to both the directions of r and F.

The SI unit of torque is newton.metre (N.m).

The magnitude of the torque depends on the values of r, F and the angle A between the two. The expression for the magnitude can be written as T = r.F sin A. It is maximum for r perpendicular to F and is zero for r parallel to F.

Answer 3

In Physics, Torque is a measure of how much a force acting on an object causes that object to rotate.

Torque can informally be thought of as "rotational force". The concept of torque, also called moment or couple, originated with the work of Archimedes on levers.

The links below will give you a detailed explanation with diagrams.

Answer 4

Torque is the ability of a force to move a body about an axis.
This is proportional to the perpendicular distance of the force from the axis of rotation and it's magnitude as well
Thus T=F*r

This is the Cross Product of F & r

Answer 5

In physics, torque can informally be thought of as "rotational force". The concept of torque, also called moment or couple, originated with the work of Archimedes on levers. The rotational analogues of force, mass, and acceleration are torque, moment of inertia, and angular acceleration respectively

Answer 6

Torque can be defined in the same way as moment. It is the product of force and perpendicular distance from the force to pivot. It creates a turning effect. In rotational motion of rigid bodies, torque is related to moment of inertia. It is the moment of inertia multiplied by angular acceleration.

Answer 7

Torque can informally be thought of as "rotational force". The SI units for Torque are newton metres although centinewton meters (cN·m), foot-pounds force (ft·lbf), inch pounds (lbf·in) and inch ounces (ozf·in) are also frequently used expressions of torque

Answer 8

Torque is the time-derivative of angular momentum, just as force is the time derivative of linear momentum.

Also,Torque is part of the basic specification of an engine: the power output of an engine is expressed as its torque multiplied by its rotational speed.

Answer 9

Torque is the effect of rotational force.

Answer 10

in rotational motional torque is the product of force and distance from the axis of rotation. It literally means the turning effect of force .