7 votes

Confusion In rotational dynamics

The axis of rotation is arbitrary. But generally speaking, if you pick a random point, the result will be a combination of rotation and translation. Let's consider a linearly moving particle to show ...
AccidentalTaylorExpansion's user avatar
7 votes

Where does "excess" energy go when a vehicle uses a lower gear to move at a given speed?

the amount of energy used per engine revolution is fixed (not precisely true I know) This is the error. The work per engine revolution is the torque at the engine. If the energy dissipation per wheel ...
Dale's user avatar
  • 100k
5 votes

Where does "excess" energy go when a vehicle uses a lower gear to move at a given speed?

Ignoring all losses from the gearbox on to the wheels, let’s just look at the engine. Internal combustion engines are about 30% efficient. About 65% of the energy is lost as heat, 5% as friction. ...
Rich's user avatar
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5 votes

Where does "excess" energy go when a vehicle uses a lower gear to move at a given speed?

If you are in a situation where the energy used to keep the car moving is unchanged, but you are putting more energy into the engine, then the difference must be losses in the engine. Whether you are ...
Cort Ammon's user avatar
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4 votes

Confusion In rotational dynamics

The key issue is that rate of change of angular momentum of a body about a point P is equal to the torque about P only if one of the following is true: the point P is at rest the point P is the ...
mike stone's user avatar
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3 votes
Accepted

Confusion In rotational dynamics

The relationship between torque and rotational acceleration is depended on the moment of inertia. If you calculate about a different axis, you will get a different moment, and thus a different torque....
Cort Ammon's user avatar
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2 votes

How to determine when angular momentum is conserved and when torque is zero?

Angular momentum is always conserved for an isolated system, around any arbitrary point you choose. If you have 4 wheels on a car, for example, it won't be convenient to consider the angular momentum ...
Señor O's user avatar
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2 votes
Accepted

In equation of torque and angular momentum what is the position vector exactly

The $r$ in the equations for angular momentum or torque for example, is a position vector, however, the specifics of the vector depend on the problem you are working. For example, if you are wanting ...
Albertus Magnus's user avatar
2 votes
Accepted

How to calculate torque at the end of a lever arm?

Newton's 3rd law dictates that if a torque $T_{\rm m}$ is applied to the disk from the motor, then an equal and opposite torque $\mbox{-}T_{\rm m}$ is applied to the motor. At the same time, the ...
John Alexiou's user avatar
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2 votes
Accepted

Understanding conservation of angular momentum in relation with rotating objects

There is most certainly an internal centripetal force within the material keeping it in circular motion. In real objects, this is provided by the intermolecular/interatomic forces, which are never ...
Vincent Thacker's user avatar
2 votes
Accepted

How to determine the torque required to decelerate a rotating arm?

I would like to know if this is correct equation to look at and if there is a faster way through the use of COM. It's the correct equation, but the moment of inertia about the pivot depends on how ...
Bob D's user avatar
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1 vote

Understanding conservation of angular momentum in relation with rotating objects

There is no centripetal force acting on the ball that keeps it in circular motion This is not correct. Each part of the ball is held in place because it is connected to the surrounding parts of the ...
gandalf61's user avatar
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1 vote

Calculating torque from what a winch can lift

Since energy is conserved (and torque is in the same units, newton-meters) it would follow that we applied 3.92 J of torque This intuition is understandable but incorrect. Adding 3.92 J of potential ...
ReasonMeThis's user avatar
  • 1,779
1 vote

In equation of torque and angular momentum what is the position vector exactly

In mechanics, there are three places where this equation shows up, and it has the same geometric interpretation each time. In each case, the $\vec{r}$ is the vector from the origin (or the point of ...
John Alexiou's user avatar
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1 vote
Accepted

How to determine when angular momentum is conserved and when torque is zero?

Assume the total torque is zero, so you can calculate the normal forces and thus the horizontal forces (using zero torque plus zero net vertical force). Then the horizontal force you will get is $F=-\...
Pato Galmarini's user avatar
1 vote

Is torque due to gravity about the center of mass zero?

At the Center of gravity : $$F_1+F_2=M\,g\quad,\Rightarrow F_2=M\,g-F_1$$ the torque about the center of gravity is: $$\tau=F_1\,\cos(\psi)\,a-F_2\,\cos(\psi)\,b$$ thus $$\tau\left(F_1~,F_2=M\,g-F_1\...
Eli's user avatar
  • 12k
1 vote

Is torque due to gravity about the center of mass zero?

The equation for Torque is: $$ \tau = r \times F$$ This is another way of saying that only forces that act perpendicular to the radial direction contribute to the net torque. In the image below, the ...
cookiecainsy's user avatar

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