Good Morning! 6/5/2016 Starter: why is it that a 1000 mega gram cruise ship can float when a ½ kg rock sinks? (there are two answers really) Today we will be… –Looking at the gradesheet –And discussing why and how things float this is the beginning of our new unit on Fluids and Gases.
Why is it that a huge heavy ship can float but a small light rock sinks? Answer this question to the best of your ability in your group. The real answer is all about Buoyancy Force.
What is the force? The force is called the Buoyancy force, it is the force pushing up on objects keeping them afloat.
Where does it come from? The force comes from the liquid itself pushing up on the floating object.
Buoyancy The buoyant force acts in the direction opposite to the force of gravity, and that is why you feel lighter in the water.
Buoyancy The pressure on the bottom of a submerged object is greater than the pressure on the top (pressure increases the deeper you go). This is because there is all that water above pushing down to increase the pressure. The result of all this is a net force in the upward direction. We call this Buoyant Force!
How much force does it push up with? It pushes up with the same force that it would push up to support the water that was there before the object moved it out of the way. So the Buoyancy force is equal to the weight of the water that used to be there.
Buoyancy Achimedes’ principle states that the buoyant force acting on a submerged object is equal to the weight of the fluid the object displaces.
How can you increase it? The force is equal to the weight of the water displaced (moved out of the way) so if you move more water out of the way then you will have more of a Buoyancy force.
Buoyancy A solid block of steel sinks when placed in water. A steel ship with the same weight floats. The difference is the amount of water that each displaces that is the important thing.
A submarine changes the water it displaces by bringing it in or pushing it out this allows it to dive, rise, or float. To make the submarine rise compressed air is released to push water out of the hull this displaces more water and increase the buoyancy force.
Relating Cause and Effect As you read, identify the reasons why an object sinks. Write them down in a graphic organizer like the one below. Object sinks Weight is greater than buoyant force. Object is denser than fluid. Object takes on mass and becomes denser than fluid. Object is compressed and becomes denser than fluid. Causes Effect
Now a puzzling question Link