Buoyancy is the upward force that keeps things afloat. When placed in water, an object will float if its buoyancy is greater than its weight. And it will sink if its weight is greater than its buoyancy. Learn more about the physics of buoyancy and density
"People have been aware of objects floating on water (or sinking) since before recorded history.
For high-school and college physics students, HyperPhysics is an illustrated, hyperlinked, mind map of hundreds of physics topics.
Helicopters and airplanes depend on thrust and forward speed to fly.
"When you place a block of wood in a pail of water, the block displaces some of the water, and the water level goes up.
Although it may not be immediately apparent (at least it wasn't to me) the green boxes represent multiple-choice answers to the questions posed by each of the headlines.
