Member-only story
Gymnastics Physics: Does Simone Biles Really Jump 12 Feet Above the Floor?
I don’t know if Simone Biles is the greatest athlete of all time, but you have to admit — she’s pretty awesome. Her gymnastics routines seem to be beyond the ability of a normal human. Oh, and Simone has a height of only 4 feet and 8 inches. That’s an important consideration when you see claims that she reaches a height of 12 feet above the floor (USA Today).
It’s fine. We can use some physics to check this claim and see what’s going on. I’m actually going to use two different methods to estimate how high she jumps on her most famous tumbling pass — the triple double.
Estimating Height With Hang Time
It’s not completely trivial to measure the height of a jump without a reference point right next to the jumper. In case you haven’t seen the floor event in gymnastics, there’s really nothing next to the gymnast during a tumbling pass.
But don’t worry — we can estimate the jump height just using the “hang time”. This is the time interval starting from the instant the gymnast leaves the floor until she once again touches the floor. The key is that after she leaves the floor, there’s only one force acting on her — the downward pulling gravitational force. This means that she’s essentially just an example of projectile motion (yes, you have to ignore the air resistance force and assume she’s a point particle — but that’s fine).
In this projectile motion example, the gymnast would have an acceleration in the vertical direction of –9.8 meters per second squared (we call this value g — for the gravitational field). With a constant acceleration, we can use the following kinematic equation.
Here, y is the final position and y0 is the starting position. Since Simone starts and ends on the floor, both of these values are the same (let’s say y = y₀ = 0 meters). That’s not very helpful to find the maximum height even though I know the time. The other problem is that I don’t actually know her starting velocity (v₀). Well — I’m just going to have to use a little trick. Let’s take a look at a jump.
