Gymnasts can actually perform both of these types of rotations at the same time, which is why this sport is so fascinating to watch. In physics, this kind of movement is called a “rigid body rotation”. But obviously humans are not rigid bodies, and the maths describing such rotations is quite complicated. For the sake of simplicity, let’s limit our discussion to somersaults.
There are three types of flips: a layout, in which the gymnast keeps the body upright, a pike, in which the hips are bent at about a 90-degree angle, and a tuck, in which the knees are pulled up toward the chest.
From a physics perspective, what is the difference?
Rotation and moment of inertia
If we want to understand the physics of rotation, we need to consider moment of inertia. I know this is a strange term, but let’s start with an example of a ship. (Yes, a ship.)
Imagine you’re standing on a pier, next to a small boat that’s just floating there, unmoored. If you put your foot in the boat and push, what happens? Yes, the boat moves, but something else also happens. The boat also Become faster As it moves away, its speed changes. This change in speed is acceleration.
Now imagine you were moving along a pier and picked up a larger boat, like a sailboat. If you put your foot on that boat and pushed with the same force as the smaller boat for the same amount of time, would the boat move? Yes, it would, but because it has more mass, it wouldn’t pick up as much speed as the smaller boat.
The important property in this example is the mass of the boat. The more mass there is, the harder it is to change the motion of the object. We can describe this property as ” inertia (this is Moment of inertia(We’ll get to that in a moment).
When you push a boat, this interaction of forces and motion can be described in terms of Newton’s second law:
Illustration: Rhett Allan
