What is torque? What forces produces torque? In this article we will answer those questions and the sub topics of equilibrium and how torque fits into that. Also we will look at how to apply the formulas in Section 3 of GAMSAT Physics.
So let’s start the basics – “what is torque?” Torque is what can be thought of as a turning force. Although, strictly speaking, torque isn’t actually a force, but that’s what they can be thought of . Whenever you have an object with a pivot point which can rotate around, like a door with the hinge being the pivot point. When you turn it, you use torque to turn it. You apply a force which allows the object to turn. Now, let’s look at the formula for torque and then we would talk about what forces produce it.
You can define Torque as:
Torque = Force x Distance from pivot (perpendicular)
That can be confusing, but let’s consider a see-saw to start off with. If I apply force to a point on the see-saw, I produce torque. The distance is the space between the pivot of the see-saw and the point of application of the force. The important thing to note here is that the force and the distance or displacement are actually perpendicular to each other. They have to be perpendicular in order to generate torque. The correct way to write that is
TORQUE is the product of FORCE and its PERPENDICULAR DISTANCE
The first thing to note is that the kind of forces that produces torque is perpendicular to the distance of the plane. The second thing that we need to note is that the force cannot be on the pivot itself because that would mean that there is no displacement and hence, you cannot generate torque. The forces have to be perpendicular to the plane and some distance away from the pivot point, and that’s when you generate torque.
The larger your torque, the more turning force you have which allows your object to turn faster. For example, if you think about the door, the farther away from the hinge you push the door, with the same force, the quicker it closes. And of course, if you try to push parallel to the door, you are not going to get it to turn, that is why you have to push it perpendicularly.
So now, let’s look at Equilibrium. The idea of Equilibrium is that you are basically in a steady state. When you think about Translational Equilibrium, that’s moving up, down, left, right. You have to have a known force to do that, and that is the concept that Newton governs in his three laws.
But there is another type of Equilibrium which is Rotational Equilibrium where you have to have known torque. Again, if we go back to the see-saw example when a force is applied to a point on the see-saw downward, it is going to cause the see-saw to move in a clockwise direction, and we would have what is deemed as clockwise torque. That brings to the point where torque is always measured in clockwise or anti-clockwise direction. If this system (see-saw) was to be in equilibrium, there should be another force acting downward on the other side. The force tends to make the see-saw move in an anticlockwise direction.
If I was to tell you that this system is in Equilibrium, you could assume that the clockwise and anti-clockwise torques cancel each other out. So for Rotational Equilibrium, all the clockwise torque and the anti-clockwise torques must cancel each other out. Just like for Translational Equilibrium, the upward and downward forces or the sides to side forces must cancel each other out.
So let’s try and apply these to a concept that we are going to focus on. In the GAMSAT Physics, you can apply this in a biological context such as with the biceps or the knee or something like that. However, to make it a little bit easier, we are going to look at easier versions of those things.
In this example:
A lion and an elephant are standing at two ends of a see-saw. The lion has a mass of 500kg and stands 2m from the pivot. While the elephant has a mass of 2000kg (clockwise). The net torque is 50Nm.
The net torque is calculated as clockwise torque minus the anticlockwise torque. So if we think about it, we should have 50Nm equal the torque produced by the elephant minus the torque produced by the lion because the lion torque is going to cause the system to move anticlockwise and the elephant torque will cause the system to move in a clockwise direction.
Let X be the unknown distant of the elephant from the pivot of the seesaw:
50 = (2000×10) × X – (500×10) × 2
50 = 20000X – 10000
Collecting like terms,
50 + 10000= 20000X
10050 = 20000X
X = 10050/20000
X = 0.5m
Note: The mass of the animals were multiplied with 10m/s2 (which is the acceleration due to gravity) to give the force applied by each of the animals.
That’s how you will apply the formula to find, in this case, the distance. This is one of the examples of how to use torques.
To tackle these problems it might be helpful to look at our GAMSAT Physics Cheat Sheet.