Initial Gyroscopic Precession Using Forces

In summary: The reason you thought this, is that its what usually happens, because the surface is usually not frictionless, so it can provide horizontal forces to accelerate the CoM.
  • #1
gyroscopeq
15
0
I think I more or less understand how a gyroscope precesses--at least mathematically and in terms of torque/angular momentum.

My question here is: how does the gyroscope start precessing in the first place? The external forces on the center of mass are entirely vertical. Given that Newton's Second Law should always work, I don't see how there would not need to be an *external* force in the *horizontal* direction to get the COM initially moving in that direction. Obviously this means I am mis-understanding something. Does anyone have a good explanation of how this works and why I am wrong?

Thank you!
 
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  • #2
gyroscopeq said:
The external forces on the center of mass are entirely vertical.
You mean gravity? Is that the only external force?
 
  • #3
A.T. said:
You mean gravity? Is that the only external force?

Gravity and a normal force.
 
  • #4
gyroscopeq said:
Gravity and a normal force.
What type of gyro are you talking about? A spinning top? Why do you assume that the contact force is vertical, it the CoM moves? Or, why do you assume that the CoM wouls still move, if the contact force was vertical (friction-less surface)?
 
  • #5
A.T. said:
What type of gyro are you talking about? A spinning top? Why do you assume that the contact force is vertical, it the CoM moves? Or, why do you assume that the CoM wouls still move, if the contact force was vertical (friction-less surface)?

I am imagining the simplest case: a spinning top on a frictionless surface. Would that no longer be able to precess?
 
  • #6
gyroscopeq said:
I am imagining the simplest case: a spinning top on a frictionless surface. Would that no longer be able to precess?
Does precession imply horizontal movement of the CoM?
 
  • #7
A.T. said:
Does precession imply horizontal movement of the CoM?

Yes? The CoM moves around in a circle.
 
  • #8
As you say, Newton's laws hold at all times and for each particle in the system.
What a force does on a particle is to change its linear momentum according to Newton's second law.
Now each particle on the spinning gyroscope already has a non-zero velocity in the first place, when
gravity acts, it acts downwards, but the resultant velocity won't be directed downwards because you
have to add the change in velocity due to gravity to the already existing velocity in each of the particles composing the gyroscope.
The net result of these changes is to change the plane containing the gyrocope as time passes, i.e. making it precess.

The force of gravity accelerates every single particle in the system, and the net effect of that is to make the gyroscope precess,
if no force acted on the gyroscope, that net result would never appear, so what makes the gyroscope start to precess is in fact gravity.

Edit: I should have said that what starts precession are both gravity and the normal force, since
these are all the external forces, but the whole argument still applies.
 
Last edited:
  • #9
gyroscopeq said:
I am imagining the simplest case: a spinning top on a frictionless surface.
gyroscopeq said:
The CoM moves around in a circle.
Think again. If the surface is frictionless, does the CoM really have to move horizontally, in order for the gyro to precess?
 
  • #10
A.T. said:
Think again. If the surface is frictionless, does the CoM really have to move horizontally, in order for the gyro to precess?

It does not. For some reason I had thought the "fixed" point was the point of contact of the top on the surface, not the CoM. Now I think it makes sense. Thank you!
 
  • #11
gyroscopeq said:
For some reason I had thought the "fixed" point was the point of contact of the top on the surface, not the CoM
The reason you thought this, is that its what usually happens, because the surface is usually not frictionless, so it can provide horizontal forces to accelerate the CoM. On a frictionless surface the CoM would be horizontally fixed.
 

Related to Initial Gyroscopic Precession Using Forces

1. What is initial gyroscopic precession?

Initial gyroscopic precession refers to the phenomenon where a spinning object, such as a gyroscope, experiences a change in its orientation when a force is applied to it. This change in orientation is perpendicular to both the direction of the applied force and the axis of rotation of the object.

2. How is initial gyroscopic precession caused?

Initial gyroscopic precession is caused by the conservation of angular momentum. When a force is applied to a spinning object, the object will resist the change in its direction of rotation. This results in a change in the orientation of the object, causing it to precess.

3. What are the forces involved in initial gyroscopic precession?

The forces involved in initial gyroscopic precession are the applied force, the weight of the object, and the force of gravity. These forces act on the spinning object and cause it to precess.

4. How is initial gyroscopic precession used in practical applications?

Initial gyroscopic precession is used in various practical applications, such as in gyroscopes used in navigation systems and stabilizers in aircraft and ships. It is also used in the design of bicycles and motorcycles to keep them stable while in motion.

5. What are some factors that can affect initial gyroscopic precession?

The factors that can affect initial gyroscopic precession include the speed of rotation of the object, the mass of the object, the applied force, and the angle at which the force is applied. In addition, external factors such as air resistance and friction can also affect the precession of the object.

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