An object is buoyed up with a force equal to the weight of the liquid it displaces. This is known as Archimedes' Principle. As an example, suppose you pushed an empty (and sealed) one-liter milk carton under the water in your bath tub. Since the carton must displace (push aside) one liter of water and one liter of water weighs one kilogram, you would feel the carton pushed upward with a force of one kilogram (minus the weight of the carton). If the weight of the object is less than the weight of the fluid displaced, it floats. If the weight of the object is more than the weight of the fluid displaced, it sinks.
