Science

# Breaking Down the Physics of the Perfect Dive

One of the most popular sports at the Olympics is really a gateway into a perfect science.

Diving has gotten a lot of strange attention this year, thanks to a lack of filtration chemicals that caused the water to turn from a pristine blue to a worrisome green, which Olympic officials are claiming is no cause for concern, but which in reality might smell like farts.

Nevertheless, the show must go on. For a diver to win the gold in their respective event, they must execute a set of incredibly intricate maneuvers all within the span of a few seconds — jump off the board, rotate in the air, and hit the water at a 90-degree angle. It’s an amazing feat that also illustrates the laws of physics very elegantly.

When a diver finally leaps off the board and reaches the apex of their jump, they carry with them an angular momentum that remains constant throughout the entire fall. Momentum is the impulse an object carries when it’s moving through space — it’s a product of an object’s mass and velocity. Angular momentum is basically momentum with a rotational motion — an object’s angular velocity (how fast it’s spinning) multiplied by its moment of inertia.

Inertia is an object’s resistance to changes in its state of motion (or state of rest). So the moment of inertia is basically how much torque is required to change the angular velocity. When a diver jumps off the diving board, they need to carry with them a specific amount of torque that will allow them to rotate in the air. Torque won’t change during the fall, so its value is defined right from the initial leap.

A diver who is leaping off the platform must do so in such a way that he or she jumps into the air already possessing enough torque that will translate into an adequate amount of rotational motion. This rotational motion will result in enough angular momentum that the diver can use to spin fast enough to pull off enough tricks in the short time between jump and landing. A lot depends on the momentum you create when you force yourself off the board.

The angular momentum will remain the same while the diver is falling, but what the diver can change is his or her moment of inertia. How? By moving one’s limbs closer to the point of rotation (i.e. the center of the body), which should decrease the moment of inertia and therefore increase angular velocity. That’s why you see divers in more scrunched up tucks spinning faster. Stretching the limbs out will increase the moment of inertia, therefore decreasing the angular velocity — which is essential for a neat and flawless dive into the water.

And that brings up the last part of the dive: the splashless water entry. The sport of diving rewards water entries that slice into the pool without actually causing a lot of water to kick back up and thrash around. A diver will want to clasp their hands together and point them perpendicularly towards the water, and dive in as vertically as possible. This essentially opens up a part of the water that the entire body slides into quietly and softly.