-
Buoyancy is the force that pushes an object up when it is immersed in water, keeping the object afloat. It was discovered, along with displacement, by the Greek philosopher and inventor Archimedes of Syracuse.
An object is buoyant to the degree that its water displacement is greater than its weight. So if an object weighs 4.9 kilograms, but it displaces 5 kilograms worth of water, it will just barely stay afloat. If the object displaced 10 kilograms of water, it would be very buoyant and stay afloat easily. Life jackets work by using substances that are buoyant enough to keep not just themselves, but also the weight of a person, afloat. - One way making a life jacket is to stuff it with a very buoyant synthetic foam that doesn't absorb water. There are many materials that can serve this purpose, and compared to air-filled vests, they are very durable. Life preservers are made using the same materials.
- Air is well-known for its use in creating buoyancy. Air weighs so little when compared with water that a mere lung-full is enough to bring a swimmer to the surface. Indeed, the main reason people need life preservers at all is because people must breathe, and that exchange of air from the lungs is usually on the negative side of buoyancy. An air-based life jacket usually uses a small capsule of compressed air. When triggered, the capsule fills a bladder made of rubber or vinyl, creating an instant life jacket. Some of these jackets have manual inflation hoses, either for primary inflation or as a supplement.
