# The gymnast makes the wolf look easy to turn around.Physics shows that it is not

Yes, this is just an image-but it is really balanced.if you Run the code, You can see that it is indeed still and does not tip over. Obviously it should work-I mean, we humans always do this to stay upright.

Rotate around the axis of rotation

If the wolf turns around just to balance one foot, it may not appear in the Olympic-level beam routine. It is this rotation that makes this so difficult.

The great thing about building my three-mass mannequin is that I can also make it rotate. If you take a hard object (such as your phone or wrench) and throw it into the air, it will roll. We call it rigid body rotation. As I mentioned, physics becomes very complicated. However, if you just want to experience something great for a little bit, here is a blog post with all the details-have fun.

However, for the mass spring model, the same calculations used for balance will work well. So this is a picture of a rotating object, which has two equal masses evenly distributed. I added a vertical line to indicate the axis of rotation and to show that it passes through the balance point-the foot.

Again, I really don’t think there are any surprises here. Everything is symmetrical, balanced in the middle, and it revolves around the downward axis from the middle.

But wait! What if we rotate asymmetry? Let us see what happened. (I should mention that I added a lateral force to the bottom rotating mass so that it doesn’t “off” the support point: check it out.)

Just in case it is unclear, the object is balanced at the pivot point, but does not rotate around a fixed axis. If you want to force it to rotate around that vertical axis, you need to apply an external torque to the object or change the position of the mass. (Like I said, rigid body rotation can be very complicated.)

There is another situation in real life like this-Balance of car wheels. Even if the center of mass of the car wheel is exactly on the axis of rotation (in this case, its actual axis), the wheel can still try to swing when it rotates. The solution is to add some extra small mass to the rim of the wheel until its axis of rotation is in the same direction as the axis.