A lifejacket, or personal flotation device, is a piece of safety equipment that is essential to have when on the open water. Lifejackets are used by people undertaking water sports and boating trips and you can even find them on airplanes. They come in all different shapes, sizes and colors and have been made to fit both adults and children. The main purpose of a lifejacket it to keep a person’s head above the water. They are designed to help you stay afloat even when unconscious.
How does it work?
To understand how a lifejacket works you first need to understand some basic physics, buoyancy, or how something floats. When an object is placed into water it moves or displaces the water, the water pushes back against the object and creates buoyancy. The more water that is displaced by the object the greater the force of the water pushing back against it. For an object to float it must be able to equal its own weight by displacing enough water. For example when a person gets into a deep body of water they feel lighter and are able to float to some extent. This is because the person displaces enough water to create buoyancy. The lighter the object the less water it needs to displace to be able to float.
Lifejackets use this principle to keep a person afloat. Lifejackets are made of a light weight substance that only needs to displace a small amount of water to stay afloat. They use their extra amount of buoyancy added to a person’s natural buoyancy to keep the persons head above water. Inflatable lifejackets use air. As air is very lightweight it will only need to displace a very small amount of water to keep a person afloat. The force of the water pushing back up against the air inside the jacket will be greater than the amount of water being displaced by the lifejacket creating more buoyancy. Lifejackets used for water sports are often made of tightly packed foam. This foam is dense, lightweight and traps air when it is submerged. The foam, which generally weighs a few hundred grams, only needs to displace a small amount of water to equal its own weight making it very buoyant and a great material to use in lifejackets.