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

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99 views

Calculate torque to rotate and 84lb panel vertically from 0 - 90 degrees

I have a rectangular panel that weighs 84lb. Width (rotational axis) is about 60-inches. Height is about 32 inches. It will be lying flat and hinged (or connected to tubular motor) on the long edge. ...
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2answers
160 views

Does a body always rotate purely about its center of mass? [duplicate]

For example : A rod is held stationary in vertical position on a smooth horizontal ground and then released. Now the center of mass has velocity and acceleration and every point of the rod has some ...
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1answer
201 views

How can angular velocity be constant even when there is a torque by friction?

A cylinder at rest lying on a rough ground is given an impulse which imparts a translational velocity (no angular velocity) to it. The question goes ahead with finding time after which rolling starts ...
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1answer
125 views

How to calculate torque needed to rotate a ring held captive between two parts with a known compression force?

I'm wondering how to find the torque needed to rotate a ring that is held captive between two plates with a known friction coefficient, radius, and compression force. I'm assuming that the mass of the ...
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2answers
231 views

Magnitude of a dipole moment [closed]

I am now learning Electromagnetism, and I am doing the practice question. However I am stuck in the following question. A uniform electric field has a dipole placed in it. If you rotate the dipole ...
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2answers
269 views

Which moment of intertia do I need to calculate torque

I'm trying to calculate the torque needed to rotate an array of solar panels. I've found some formulas for calculating torque, but they require moment of inertia. I designed this array in Autodesk ...
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2answers
223 views

Is torque still a vector in 2 Dimensions?

In 3D, torque is defined as $\vec{r} \times \vec{F}$ which is a vector, therefore having both a direction perpendicular to the plane of $\vec{F}$ and $\vec{r}$ and a magnitude of $\text{F}\cdot\text{r}...
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1answer
40 views

potential energy of a segment of an ideal chain under external force

I want to construct the partition function of an ideal chain under applied external force. Let's say we apply force to both ends (with opposite sign) acting in z-direction and a segment of the ideal ...
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1answer
154 views

How to make a body rotate about a line that does not go through its center of mass by applying external torques

In space, is it possible to make a body rotate a point that does not go through its center of mass by applying external torques?
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375 views

How to work out the gravitational potential energy of rotating rod

I know that the kinetic energy of a rotating rod is $$ KE_{rot}=\frac12I\omega^2 $$ where $I$ is the moment of inertia. But is there some way to calculate gravitational potential energy using just ...
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2answers
329 views

A lever arm-definition question

My question is regarding Torque, and specifically the definition of the lever arm. As far as I've understood, the lever arm is the line perpendicular to the line of action to your reference point. ...
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0answers
78 views

How to determine how much torque a hollow cylinder can take?

I'd like to calculate how much torque a hollow cylinder along its axis can take before it will start to buckle. The cylinder is held at one end, and the torque is applied equally in discrete ...
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1answer
127 views

Torque-direction of rotation

Taking moment about $A$, the mass of 2.0g and 0.50g is rotated in the clockwise direction is because they are both directed in downwards position? while $R2$ is acted in upward direction, so it is ...
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3answers
121 views

Can the anti-torque of a motor be used to spin a space vehicle about it's axis?

Imagine an electric motor together with its power supply in space. What exactly will happen to it if it is suddenly powered? Will it spin about its axis, or it will experience no motion relative to an ...
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1answer
61 views

Drag in low earth orbit

So I'm looking at the following problem; Arrow type configuration in orbit. Each end of the arrow has a mass and a cross sectional area (we can assume the head and tail are connected by a ...
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1answer
232 views

Torque Approximations Neglecting Friction

Disclaimer: I'm not asking for homework help. I don't understand how my calculations work out conceptually. If you can help me understand the connection between the concepts, I'd really appreciate it. ...
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2answers
163 views

Generalization of torque and angular momentum

Question: in the simple equations $\tau = r \times f$ and $L = r \times p$, what is the origin of the vector $r$? In many textbook discussions on rotation of a rigid body about a fixed axis, $r$ is ...
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2answers
96 views

Balancing torques in a free body diagram: What point should they be in equilibrium about

I have an object that is mounted securely so that it cannot move, which is then loaded by an external force. I would like to determine the forces acting on the mount points. Since the object is not ...
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1answer
1k views

Finding the magnetic moment of a permanent magnet to calculate the torque when exposed to a magnetic field

A permanent magnet has a magnetic moment $m$ associated with it. When exposed to a magnetic field $B$ the torque acting on the magnet can be calculated as $\tau = m \times B$. I am trying to ...
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0answers
122 views

Torque on a wire loop from straight wire [closed]

I need to show that the torque on this wire loop is $$N = \frac{\mu_0}{\pi} 2abdII' \frac{(b^2+d^2)\sin(\theta)}{b^4+d^4-2b^2d^2\cos(2\theta)}$$ The where $\theta$, is the angle between the loop ...
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0answers
66 views

Find the force and the torque so that the cylinder is in balance

At the cylinder of the picture there are static pressures from environment fluid of density $\rho$. If we neglect the atmospheric pressure, calculate how much force and how much torque is needed so ...
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2answers
122 views

Torque (in $Nm$) of a cyclist

We're discussing bicycles with a friend, and it came to safety, speed and power. Now the question we have is: how much torque do my legs provide to the bicycle? I'm no expert in physics sadly, and ...
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1answer
302 views

Free Body for object on vertical wall, Applied force, Torque required for motion [closed]

I am trying to understand how to create a correct Free Body diagram and understand formula used to forces acting on object (i.e. a robot with 4 wheels) that is "placed" on vertical surface such as a ...
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2answers
237 views

Connection between moment/torque and centre of gravity?

So I understand how moments work with regards to basic examples like pushing a door, in that the further you are away from the hinges of the door, the greater the moment, which is like a turning force....
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1answer
362 views

Torque in a non-inertial frame

How can we calculate torque in a non-inertial frame? Take for instance a bar in free fall with two masses, one on either end, $M_1$ and $M_2$. Taking the point of rotation to not be the center of mass,...
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1answer
372 views

difference between magnetic dipole moment and torque on a magnetic dipole?

I am a bit confused. What is the difference between magnetic dipole moment and torque on a magnetic dipole ?
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90 views

Where does the center of mass torque come from?

When calculating the torques about a pivot point, there is a torque that comes about if you aren't rotating about the center of mass- where does this torque physically come from? For instance, given a ...
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1answer
258 views

How do we “cancel out” the torque from running?

Running certainly causes a torque on our body, as we are propelled forward via our feet; why doesn't this torque cause our bodies to spin about their center of mass?
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1answer
1k views

Why does a diver changes his body positions before and after diving?

Before a diver dives in a pool, he changes his body positions several times. When he is about to jump from board he extends his arms and legs but sometime after jumping he closes his body in a ...
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1answer
37 views

What happens with an originial force if a part of it creates a torque?

Let's say I push with an angle of 45 degrees at an object with a force of 100 N. Since the angle is 45, we would have a torque $\tau = 100 * sin(135) * r = 71N*r$ Since the force was not ...
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1answer
90 views

If $\omega = \frac{v}{r}$, why do we need torque?

If $\omega = \frac{v}{r}$, then why do we need torque and angular acceleration? The velocity v can be found just by Newton's second law of motion $F = ma => a = F/m$ and $v = v_0 + at$ . Then we ...
2
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2answers
113 views

Formula for balance with three arms?

I'm searching for a way to express the angle of the arm of a balance instrument expressed in the weight that is present in one arm. For a two legged balance one could use the moment formula: moment = ...
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2answers
103 views

Wheelie physics part 2

Okay, so I got some really great advice from the community here but I am still hung up on some conceptual problems. I posted earlier trying to determine the axis that a bicycle rotates about when ...
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1answer
638 views

How can I set up an equation for distance traveled for a rubber band powered car?

I am to make a rubber band powered car, and I have to maximize it's distance traveled. The time taken to reach said distance, top speed of the car, acceleration of the car, is not relevant. I just ...
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1answer
172 views

Movement and Rotation of a Inverted-Pendulum-like Object with External Forces

I'm struggling to model the movement of a complex object based on an external force. Let's start with a simple example of what I'm looking for. We have a block $b$ of mass $M_b$, moving friction-...
2
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1answer
63 views

To which side will it move? [closed]

Children pull the carousel with diverse forces (as in the picture below). In which direction will the carousel move? Calculate the torque. I have done the following: The torque of the force that ...
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2answers
958 views

How does a wheelie work?

So I've been trying to create a mathematical model for an electric motorcycle and began to wonder about the maximum possible torque that could be supplied to the rear driven wheel without having the ...
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0answers
62 views

Total angular momentum of a continuous body

I find the definition of total angular momentum $\mathbf{L}$ of a system of $n$ material points with respect to a given point $Q$ as the sum of the momenta $\ell_i=\mathbf{r}_i\times\mathbf{p}_i$ -...
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4answers
1k views

Paradox in applying Newton's second law [duplicate]

Suppose I apply two vertical but opposite forces with the same magnitude in a body like is shown in the picture: According to newton's second law, the center of mass shouldn't accelerate, since the ...
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1answer
190 views

Torque considered about different points in a system [duplicate]

If we consider the torque about point A, there is none, so there is no rotation about point A. If we consider torque about point B, there is a net torque which means that there is rotation about point ...
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2answers
143 views

Clarify an assertion on torques from the Feynman lectures

In The Feynman Lectures, vol.I, chapter 18, Feynman discusses torques on a rigid body in two dimensions and says: Now we pause briefly to note that our foregoing introduction of torque, through ...
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1answer
96 views

Angular acceleration of two rods joined in the center - did I do this right?

The question is: The moment of inertia of a thin rod of length $l$ and mass $M$ about a perpendicular axis through its center is $\frac{1}{12}Mt^2$. The object shown consists of two ...
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3answers
884 views

How can I relate linear and angular motion using a single formula?

I want to relate linear and angular motion using a single formula. Assume I have a 10m rod, and I apply a force of 5N on it, 2.5m away from the axis of rotation for 1s. How can I determine the ...
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3answers
410 views

Torque on a disc?

In the following diagram: Point(c) is a going into the page and attached to the disc, Point(c) applies a torque($\tau$) to the disc, and it starts to rotate due to that torque. And if point(c) was ...
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2answers
46 views

When I change the rpm of a turntable, how long does the turntable to get to the new rpm?

If the turntable was rotating at 16 rpm and I switched it to 30 rpm, is the change in speed pretty much instantaneous, or is their a period of acceleration? When I did it, the change appeared to be ...
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1answer
213 views

Rotational Equilibrium Problem [closed]

The question is as follows: One end of a uniform 4.0-m rod, whose weight is w, is supported by a cable that makes an angle of 37° with the horizontal. The other end of the bar rests against a wall ...
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2answers
151 views

Can net torque $\sum_i\mathbf r_i\times\mathbf F_i$ be expessed as $\mathbf r\times$ (net force) for some $\mathbf r$?

Let $\mathbf F_i$ be forces each of which is applied on $\mathbf r_i$ of a rigid body. Then is there a position vector $\mathbf r$ that satisfies $$\displaystyle\sum_i\mathbf r_i\times\mathbf ...
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0answers
28 views

The torque produced in the rotor blades of an axial flow turbine

I want to ask about the torque experienced by a axial flow turbine, and how the torque is related to the ange of attack, or pitch angle of the turbine blades. (I'm new to technical terms, please ...
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5answers
3k views

Why is it easier to go uphill on a lower gear?

In cars as well as bicycles, when we are on a lower gear, the driving wheel (the one on the wheels) has a bigger radius compared to when on a higher gear. So on a lower gear the bike/car would move ...
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2answers
134 views

Instead of a dynamo-meter, why can't we use $\tau=I\alpha$ to determine the power of a rotating shaft?

To measuring the power of a rotating shaft, dynamo-meters are used. Instead, why can't we find torque using Torque=Moment of Inertia times Angular Acceleration, $\tau=I\alpha$? And given that we know ...