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Direction of Torque
We can classify torques as clockwise or anticlockwise if we look down the axis of rotation. Anticlockwise torques are treated as positive. Clockwise torques are treated as negative.
Adding Torques
The net torque on an object is the sum of all the torques acting on it. Clockwise and anticlockwise torques cancel each other out. This is why we treat them as positive and negative quantities.
Torque and Force
Remember that torque and force are different quantities. Force is measured in Newtons, but torque is measured in Newton-metres. Force can only produce a torque when it is perpendicular to the axis of rotation.
00:00
So, we can classify torque as clockwise or anti-clockwise, depending on which direction they're going. Right? We can talk about anti-clockwise torque being positive, and clockwise torque as negative, just as a convenient convention. Right.
00:22
Now, first, this might seem a little confusing, but remember that if we're ever talking about angles in mathematics, we can often talk about them as part of a circle. And if we were to draw a circle around here, and say that going straight across zero, then when we increase the angle, we can talk about raising up the thing like that. So, going anti-clockwise is positive torque. Right?
00:55
Now, the reason that we talk about them as positive and negative is because we're able to add them together. And having them positive and negative makes that a little easier to do. If we're talking about the direction.
01:12
The net torque of an object you see is the sum of all the talks acting on it. So, if we have one talk, turning a spinner in one direction, and another talk trying to turn the spin and back in the other direction, then we can add them together and see the torques are going to cancel out.
01:29
On the other hand, if we have two different talks, pushing a spanner in the same direction, then the net torque on that spanner will be greater than either of the individual torques. So clockwise and anti-clockwise torques will cancel each other out. And this is why we can treat them as positive and negative. Because positive and negative numbers, just like clockwise and anti-clockwise torques will cancel each other out.
01:56
We can see an example of two torques cancelling each other out in this photograph over here. If the torque on one side of the barbells was greater than the whole set of barbells would sort of start to rotate and fall down to one side, assuming we held them right in the middle. But because there's equal torque from both the right side and the left side, the net torque on the weight is absolutely zero, so it doesn't turn left or right. It just moves in a straight line. And in fact, it would travel straight down if it weren't being held up.
02:38
So, I'll just repeat it again. Torque and force are not the same things. Torque causes objects to turn or rotate and force causes objects to move. So, force is measured in Newtons, but torque is measured in Newton meters. Because we calculate Newton by-- we calculate torque by multiplying a force in Newtons by distance in meters.
03:10
So, the force can only produce torque when it is perpendicular to the axis of rotation. That means that if we take a spanner and we try to push it forward toward the axis of rotation is not going to turn. So, this will be an important property of talk when we talk about motors and generators and how they can turn.
0:00 Introduction
0:01 Direction of Torque
1:11 Adding Torques
2:38 Torque and Force
