This article is the second in the "Floaty Feet & Playground Physics" series. If you haven't already, check out The Basics of Perfect Diving Trim, Part 1.
Playground toys can teach you the basics of good scuba diving trim.
Seesaws. Teeter-totters. Known by different names, these have been well-known fixtures on children’s’ playgrounds for a long time. When I was 5, my friends and I called them catapults, as we thought the main purpose of the seesaw was to launch smaller kids across the playground. Everyone involved thought this was great fun, up until kids started hitting the ground sideways.
Within weeks, the teachers put a stop to the game “How high can Jimmy fly?”, thereby completely spoiling what had really been an awesome game.
Once we were forced to play on the seesaws the “normal” way, it didn’t take long for us to notice that the things didn’t work so well when one kid was significantly bigger than the other. The smaller child would be stuck up in the air while the big kid sat on the ground, or at least until the bigger kid jumped off the seat and laughed as gravity took control of situation. At any rate, we didn’t want to sit still: we wanted the teeter-totter to go up and down really, really fast.
We tried to solve this problem a few different ways, with varying degrees of success.
1. Move the big kid close to the center of the seesaw
This was quickly determined to be the worst idea ever as we still had the same problem, but reversed.
2. Put two smaller kids on one end to balance things out
Undeterred, someone posed a brilliant question: what if we put two smaller children on one end of the seesaw, with only one bigger child on the other. This resulted in balancing things out rather well, as the weight on either end of the seesaw was closer to being equal. We learned that loading up the ends with extra kids, i.e., weight, really made for a wild ride as it was easier for us to move up and down faster.
3. Have the big kid move closer towards the middle of the seesaw.
This completely blew our minds, as doing so seemed to balance the seesaw even though the kids were nowhere near the same size! There was a weird side-effect, however: the seesaw was not as much fun to ride. The closer the children were to the middle, the harder it was to make the beam pitch wildly back-and-forth.
As five-year old adrenaline junkies, we were not amused and quickly reverted to piling multiple children on each end of the seesaw until someone broke an arm.
Interestingly enough, it was this boring approach to playground equality that would prove to be the secret to all sorts of excitement years later, once I began diving.
Of course sometime after 1st grade but before my open water class, I learned that a seesaw was really just an over-sized version of a common simple machine: a lever. The kids were just acting as weight on either side of a fulcrum, or balance point.
When we dive, our body is like one big seesaw.
Just like the kids on the playground lever, our legs, lungs and equipment are the forces working against each other.
Additionally, the diver has a different goal than the children on the seesaw. While we (the kids) wanted to go up and down really fast, while the diver wants stability. An excellent diver doesn’t drift, pitch or roll any particular direction unless they want to.
If things are out of balance one way, the diver will struggle with floaty feet. If the balance is off in the opposite direction, they’ll feel feet heavy. The goal is to understand how the diver’s gear and body positioning affects the balance of the “seesaw”.
Here’s a picture of me diving the USS Oriskany, south of Pensacola, Florida.
The same picture, showing the ‘seesaw’ layered over the photo along with with relative weights that are being kept in balance:
It really is that simple!
In part 3, we’ll take a look at the various factors that can affect a diver’s trim, as well as how you can balance things out without having to buy any new scuba gear.
Till next time!