The forces at work in buoyancy. Note that the object is floating because the upward force of buoyancy is equal to the downward force of gravity. In science, buoyancy ( /ˈbɔɪ.ənsi, -əntsi/ or /ˈbuːjənsi, -jəntsi/;) or upthrust, is an upward force exerted by a fluid that opposes the weight of an immersed object.