Buoyancy

In science, buoyancy (pronunciation: /ˈbɔɪ.ənᵗsi/ or /ˈbuːjənᵗsi/; also known as upthrust) is an upward force exerted by a fluid that opposes the weight of an immersed object. In a column of fluid, pressure increases with depth as a result of the weight of the overlying fluid. Thus the pressure at the bottom of a column of fluid is greater than at the top of the column. Similarly, the pressure at the bottom of an object submerged in a fluid is greater than at the top of the object. This pressure difference results in a net upwards force on the object. The magnitude of that force exerted is proportional to that pressure difference, and (as explained by Archimedes' principle) is equivalent to the weight of the fluid that would otherwise occupy the volume of the object, i.e. the displaced fluid.

For this reason, an object whose density is greater than that of the fluid in which it is submerged tends to sink. If the object is either less dense than the liquid or is shaped appropriately (as in a boat), the force can keep the object afloat. This can occur only in a reference frame which either has a gravitational field or is accelerating due to a force other than gravity defining a "downward" direction (that is, a non-inertial reference frame). In a situation of fluid statics, the net upward buoyancy force is equal to the magnitude of the weight of fluid displaced by the body.

Bill Nye

William Sanford "Bill" Nye (born November 27, 1955), popularly known as Bill Nye the Science Guy, is an American science educator, comedian, television presenter, actor, writer, scientist, and former mechanical engineer, best known as the host of the Disney/PBS children's science show Bill Nye the Science Guy (1993–1998) and for his many subsequent appearances in popular media as a science educator.

Early life and education

Nye was born on November 27, 1955, in Washington, D.C., to Jacqueline (née Jenkins; 1921–2000), a codebreaker during World War II, and Edwin Darby "Ned" Nye (1917–1997), also a World War II veteran, whose experience without electricity in a Japanese prisoner-of-war camp led him to become a sundial enthusiast. His maternal grandmother was French, from Dancevoir.

After attending Lafayette Elementary and Alice Deal Junior High in the city, he was accepted to the private Sidwell Friends School on a partial scholarship and graduated in 1973. He studied mechanical engineering at Cornell University (where he took an astronomy class taught by Carl Sagan) and graduated with a B.S. in mechanical engineering in 1977. Nye occasionally returns to Cornell as a guest-lecturer of introductory-level astronomy and human ecology classes.