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# Questions tagged [torque]

The tendency of a force to rotate an object about an arbitrary axis.

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45k views

### Why is torque not measured in Joules?

Recently, I was doing my homework and I found out that Torque can be calculated using $\tau = rF$. This means the units of torque are Newton meters. Work & Energy are also measured in Newton ...
8k views

### Hanging a hammer from a table and a stick so that its midpoint is outside of the support of the table

I came across this pic on the internet today. At beginning I thought it is just not possible because the centre of mass is way off so gravity will generate torque making the stick and hammer fall. ...
6k views

### Is torque as fundamental a concept as force?

I used to think that torque and force were equally “fundamental”. In other words, my understanding was that we usually use Cartesian coordinates in many common problems because it is a convenient ...
13k views

9k views

### How much force is required to propel a bicycle?

A friend of mine had an idea to attach a motor to a bicycle with the idea to be able to turn it on and have it maintain average bike speed, apparently 15-20 mph. Neither of us have taken physics ...
7k views

### Is torque independent of choice of the point of rotation?

Is torque or moment of a couple independent of the choice of point of rotation? Torque is given by $\tau =\vec r\times\vec F$. It depends on $\vec r$, which is the position vector from the axis of ...
25k views

### Why is less force required to open a door when we apply a force at a greater distance from the hinge?

I know that the magnitude of a torque increases with the distance from the axis of rotation. What is the reason of that : how can a force exert a greater torque when the force is applied at a ...
1k views

### Why do things spin?

Let's say I have 2 boxes, one of mass M and one of mass 2M. They are separated by a distance of 1 meter. I drop them from the same height and see that due to the earth's gravity, they accelerate at ...
413 views

### Balancing an orange on a spoon experiment

I did a little experiment with balancing an orange on a spoon. And i realized i don't really understand why i feel a stronger force under both fingers, the further my forefinger is from the orange (...
169 views

### Is the net torque changed when a partner on a seesaw stands or hangs from her end instead of sitting?

Is the net torque changed when a partner on a seesaw stands or hangs from her end instead of sitting? (Does the weight or the lever arm change?)
33k views

### Ball Rolling Down An Inclined Plane - Where does the torque come from?

There is a ball rolling down an incline, with no slipping. If we consider the point of contact between the ball and the inclined plane to be the pivot point (for our torque calculations), then I have ...
3k views

### finding angular velocity and regular velocity when bouncing off a surface with friction

Take the game of pong as a simple example. When you hit the ball with a paddle that has a frictional surface, the ball will spin as well as change direction according to the coefficient of kinetic ...
180 views

### Why does this screwdriver roll in a curved trajectory?

I am trying my level best to give this screwdriver a horizontal push only, but it is going in a circular path. I thought of uneven friction due to non-uniform normal reaction...what do you think? I ...
463 views

### Does it require a torque to spin a rectangular plate around its diagonal?

If a rectangular plate is rotating aroud its diagonal, one can find its inertia tensor and see that the angular momentum vector is changing in time. Thus it should require a torque to keep spinning, ...
5k views

### What is rotational potential energy?

I don't understand the concept of rotational potential energy. During linear motion, when a force is applied, the work it does gets converted to kinetic energy and there is no change in the ...
887 views

### How does a lever magnify force? [duplicate]

I understand that energy is conserved when a force is applied to the end of a lever and magnified closer to the pivot point. However, I would like to know how it is the force is transferred and ...
2k views

### Conservation of angular momentum experiment

I've learned in that in this experiment: ...the skater will start rotating faster when she brings her arms in and there is no net torque acting on her. But what would happen to her angular momentum ...
18k views

### Proving angular momentum is conserved for a particle moving in a central force field $\vec F =\phi(r) \vec r$

A problem I am trying to work out is as follows: A particle moves in a force field given by $\vec F =\phi(r) \vec r$. Prove that the angular momentum of the particle about the origin is constant. ...
2k views

### Why is torque sometimes reported in kg m, instead of the usual N m?

On various websites I see torque expressed as $\rm kg\: m$, but I was always thought that torque is $\rm N\:m$ or $\rm kg\: m^2/s^2$. These are clearly not the same, so why are they called the same, ...
1k views

### What is a moment?

As a 8th grader I am still a newbie at science and I have problems understanding the forces that I can not imagine and one of these "forces" is the moment. We are told that, $$\text{moment}= Nm$$ ...
13k views

### Why is a clockwise moment negative by convention?

My physics book states that by convention a clockwise moment is said to be negative and an anti-clockwise moment is said to be positive. I'm curious about the origin of this convention. My thoughts: ...
1k views

### Meaning of the direction of the cross product

I was doing calculations with torque and then I came across something very confusing: I understand that the magnitude of the torque is given by product of the displacement(from the center of rotation)...
435 views

### Considering the theory of special relativity: Is torque still a vector?

Considering the theory of special relativity: Is torque still a vector? In classical mechanics it is easy: You have 3 axes and thus 3 planes. Every plane has its own torque so torque has 3 ...
If a system of particles is given, in a 2D plane, with particles having masses $M_1$, $M_2$, $M_3, \ldots M_n$ and coordinates $(x_1,y_1)$, $(x_2,y_2)$, $(x_3,y_3), \ldots (x_n y_n)$, then how can one ...