Why Does Torque Point Perpendicular in Gyroscopic Precession?

[Lego Science]

Veritasium posted a video on his YouTube channel called "Gyroscopic Precession." () In the video he explained how spinning the wheel caused the torque tho point toward "the camera" at 90° to the angular momentum. My first question is how and why does the torque point perpendicular to the wheel. My second question is why the torque force points to "the camera" and not the opposite direction, to me it seems like either direction would be kind of the some to the wheel. Please elaborate.

 

[paisiello2]

The torque is a rotation about an axis and the axis is perpendicular to the wheel.

The reason the torque vector points to the camera and not the opposite direction is pure convention. It could easily be the other direction as well and nothing would change as long as you are consistent throughout with whatever convention you pick. In this case he used the well established convention of the "right hand rule".

 

[Lego Science]

Thank you paosiello2. As I have done more reading I have thought that maybe the reason the torque points toward the camera is because the wheel is spun around the rope holding the wheel, and the torque favors the centripetal force direction? I also have another question: The wheel spun counter clockwise (from the front) and the wheel spun around the rope counter clockwise, is this always a direct correlation?

 

[paisiello2]

Thank you paosiello2. As I have done more reading I have thought that maybe the reason the torque points toward the camera is because the wheel is spun around the rope holding the wheel, and the torque favors the centripetal force direction?

No, it is only a convention. It could easily point away from the camera as well. As long as you suddenly don't change the convention you adopted from the start then you will always end up with the same answer.

The centripetal force direction is not really the issue. It's more the fact that you have a rotation vector of the wheel being added to the rotation vector of gravity acting on the wheel.

I also have another question: The wheel spun counter clockwise (from the front) and the wheel spun around the rope counter clockwise, is this always a direct correlation?

Yes, there is always a correlation. Here is my understanding of what is going on:

Gravity creates a torque about one axis. As the wheel starts to swing down caused by this gravitational torque, the spin of the wheel creates a restoring torque that momentarily also causes a slight rotation about the axis of the rope. As long as this gravitational torque acts on the spinning wheel then their will be this rotation about the axis of the rope. This rotation is technically called a precession.

 

[pmacias]

I can provide some insights to your questions about gyroscopic precession. First, it is important to understand that gyroscopic precession is a phenomenon that occurs when a spinning object is subjected to a force. This force causes the object to rotate around a different axis than the one it is spinning on. In the case of the spinning wheel in the video, the force applied is the torque from the hand pushing on the wheel.

Now, to answer your first question about why the torque points perpendicular to the wheel, we need to look at the concept of angular momentum. Angular momentum is a property of a rotating object that describes its tendency to keep rotating in the same direction. In this case, the wheel is spinning in a certain direction and has a certain amount of angular momentum. When the hand applies a force to the wheel, the direction of the force is perpendicular to the direction of the angular momentum. This causes the wheel to rotate around a different axis, resulting in gyroscopic precession.

As for your second question about why the torque force points towards "the camera" and not the opposite direction, it is important to remember that the direction of the torque is always perpendicular to the direction of the applied force. In this case, the hand is pushing on the wheel from the side, causing the torque to point towards "the camera" or towards the observer in the video. If the hand were to push from the opposite direction, the torque would point in the opposite direction as well.

In summary, the direction of the torque in gyroscopic precession is dependent on the direction of the applied force and the direction of the object's angular momentum. This results in the torque pointing perpendicular to the object and in the direction of the applied force. I hope this explanation helps to clarify the concept of gyroscopic precession for you.