Final answer:
To ensure safety, the flotation device should be adjusted using straps and buckles to fit snugly at the waist to prevent it from moving up near the ears in the water, much like how surface tension supports a needle on water.
Step-by-step explanation:
To adjust your flotation device, use the straps and/or buckles to make sure that it fits comfortably yet snugly at your waist. This will keep the flotation device from moving up too close to your ears if you end up in the water. A properly adjusted flotation device is essential for safety in the water and to ensure that it provides the necessary buoyancy. A good fit is comparable to how a needle on top of a glass of water is kept afloat by the surface tension of water, supporting its weight without sinking, much like a water strider on the surface layer of water.