# How does angular momentum create a perpendicular force?

• chi-young
In summary, the behavior of a quickly rolling wheel on a string is explained by the molecules of an atom taking an "all for one and one for all" vow to maintain balance. The spinning parts of the wheel have linear momentum that is canceled out by the string on the axle, which ties the wheel to a fixed point. This causes the wheel to precess at a constant rate, creating a torque that opposes the force of gravity. The angular momentum of the wheel does not create a force, but rather the precession creates a torque that counteracts gravity and keeps the wheel from falling down. This concept is also seen in single rotor helicopters, where the cyclic control must be advanced by 90 degrees to compensate for the precession-like reaction

#### chi-young

The experiment of a quickly rolling wheel on a string is well known.

How is this behavior explained in terms of the molecules of an atom? That is to say, why don't the individual atoms of the wheel fall down?

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It is because the atoms are mouseketeers and they took an all for one. and one for all vow to get into to wheel fraternity. Actually the spinning parts of the wheel only have linear momentum, linear momentum at the bottom half is canceled by linear momentum in the top half. The string on the axel of the wheel ties the wheel to a fixed point, if the wheel was to rotate down that would change the linear momentum, but since the linear momentum is conserved, it causes the torques that the professor explained better than I can.

One way to look at the situation is to note that velocity change is the result of an acceleration applied over some period of time. In the case of a wheel in a precessing mode due to wheel rotation and external torque, the velocity change component perpendicular to the plane of rotation of a point on the wheel lags the change in acceleration component perpendicular to the plane of rotation by about 90° as the wheel rotates and precesses.

The end result is that the reaction of a spinning wheel to an external torque will be a precession about 90° "after" the torque. This effect applies to a single rotor helicopter, so the "cylic", which controls roll and pitch rotation, is advanced by 90° from the pilot input to compensate, and the helicopers roll and pitch responses are precession like reactions to torque inputs from the rotor blades.

The reason while the wheel doesn't fall down is that the torque due to gravity and the line holding the wheel up is opposed by an equal and opposing torque if the wheel is precessing at a constant and "proper" rate. The other situation is that the free axis end of the wheel will oscillate up and down as the rate of precession increases and decreases.

The other interesting bit here is that the center of mass of the wheel will tend to stay on the same horizontal plane moving the free axis up or down depending on the movement of the supporting line and how far off from vertical the supporting line is at any moment (the ideal situaion would be a massless supporting line). Look at video #9 on this web page for an example of this:

http://www.gyroscopes.org/1974lecture.asp

Video #18 on that same web page has small masses located at the ends of the spokes that demonstrate the explanation I gave above, but in the video the effect is noted but not explained.

how does angular momentum create a perpendicular force?
It doesn't create a force, the precession creates a torque that opposes the torque due to the supporting line and gravitly, so that the wheel doesn't rotate "downwards", and the vertical component of tension in the line is what opposes gravity.

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This might help:

Angular momentum is a fundamental concept in physics that describes the rotational motion of an object. It is a product of an object's mass, velocity, and distance from the axis of rotation. When a wheel is rolling quickly on a string, it possesses a significant amount of angular momentum due to its high velocity and distance from the axis of rotation. This angular momentum creates a perpendicular force on the wheel, causing it to resist falling down and instead continue rolling along the string.

In terms of the molecules of an atom, this behavior can be explained by the concept of inertia. The individual atoms of the wheel have their own angular momentum due to their mass and speed of rotation. This angular momentum causes them to resist any changes in their state of motion, including falling down. Therefore, even though the wheel is rolling at a high speed, the individual atoms maintain their relative positions and continue to rotate in the same direction, creating the perpendicular force that keeps the wheel rolling.

Furthermore, the shape and structure of the wheel also play a role in its ability to roll and resist falling down. The molecules of the wheel are arranged in a way that distributes the weight and angular momentum evenly, allowing it to maintain its balance and continue rolling without falling down.

In summary, the concept of angular momentum and the principles of inertia and molecular structure help explain how a quickly rolling wheel on a string can resist falling down and continue rolling along the string.

## 1. How is angular momentum related to perpendicular force?

Angular momentum is a property of a rotating object that describes its tendency to continue rotating. When an object with angular momentum experiences a change in its rotation, it also experiences a perpendicular force, known as a torque. This is due to the conservation of angular momentum, which states that the total angular momentum of a system remains constant unless acted upon by an external torque.

## 2. How does angular momentum create a torque?

Angular momentum can be thought of as a vector quantity, with both magnitude and direction. When an object with angular momentum rotates, the direction of its angular momentum vector remains constant. Any change in the rotation of the object will result in a change in the direction of its angular momentum vector, creating a perpendicular force or torque.

## 3. Can angular momentum and torque be applied to non-rotating objects?

No, angular momentum and torque are specific to rotating objects. Non-rotating objects do not have angular momentum, and therefore do not experience torque. However, if a force is applied to a non-rotating object, it may begin to rotate and therefore have angular momentum and experience a torque.

## 4. How is angular momentum and torque used in real-world applications?

Angular momentum and torque are essential principles in physics and are used in many real-world applications. For example, they are crucial in understanding the motion of planets and satellites in space, the stability of rotating objects such as gyroscopes, and the movement of fluids in turbines and engines.

## 5. Can angular momentum and torque be changed or manipulated?

Yes, angular momentum and torque can be changed or manipulated by applying a force at a specific distance from the axis of rotation. This is known as the moment arm and can be increased or decreased to change the amount of torque experienced. Additionally, the distribution of mass in a rotating object can also affect its angular momentum and resulting torque.