Re: 100 lb of Lead Vs 100 lb of concrete
Here's one for the engineers.
Does an object really weigh less once submerged? That implies an elimination of mass. It is subject to an opposing force (buoyancy). Does an aircraft weigh less when airborne because of lift?
Having taught deep wreck diving when I was younger, I get the concept being discussed. Just a question of technical clarity on whether something actually weighs less. I don't think so. I think it's really a case of opposing forces that makes the object appear to weigh less.
It all depends on what definition one is using: mass, weight, or apparent weight. Mass
is a measure of the inertia of an object. Weight
is the force an object exerts in a gravitational field (weight = mass x gravity; we talk about an object "weighing" so many kilograms, but in fact the proper units of weight are newtons). For a body at rest, apparent weight
takes buoyancy into account. The buoyancy provided by air is small enough, and gravity is constant enough, that our operational use of apparent weight to estimate mass is sufficient for most applications. However, as this thread demonstrates, there are exceptions.
Never forget them. Do something to prevent it from happening again.
Charlotte Bacon, Daniel Barden, Rachel Davino, Olivia Josephine Gay, Ana M. Marquez-Greene, Dylan Hockley, Dawn Hochsprung, Madeleine F. Hsu, Catherine V. Hubbard, Chase Kowalski, Jesse Lewis, James Mattioli , Grace McDonnell, Anne Marie Murphy, Emilie Parker, Jack Pinto, Noah Pozner, Caroline Previdi, Jessica Rekos, Avielle Richman, Lauren Rousseau, Mary Sherlach, Victoria Soto, Benjamin Wheeler, Allison N. Wyatt
Last edited by SlowButSteady; 04-22-2013 at 07:48 AM.