1. Buoyancy & Pressure
Ch 2 Section 3

2. Pressure is the amount of force exerted on a given area of surface.
You probably have heard the terms air pressure, water pressure, and blood pressure.
Pressure is the amount of force exerted on a given area of surface.

3. Fluids exert pressure evenly in all directions.
For instance, when you add air to a bicycle tire, you push air into the tire. Inside the tire, tiny air particles push against each other and against the walls of the tire.
The more air you pump into the tire, the greater the number of air particles pushing against the inside of the tire and the greater the pressure is. Pressure can be calculated by dividing force by the area over which the force is exerted.

4. Pressure = force/area
The SI unit of pressure is the pascal. One pascal (1 Pa) is the force of one newton exerted over an area of one square meter (1 N/m2). The newton is the SI unit of force.

5. All fluids exert an upward buoyant force on matter.
If you push a rubber duck to the bottom of a bathtub, the duck pops to the surface when you release it. A buoyant force pushes the duck up.
Buoyant force results from the fact that pressure increases with depth. The forces pushing up on an object in a fluid are greater than the forces pushing it down. Thus, there is a net upward force: the buoyant force.

6. Archimedes’ principle is used to find buoyant force.
The buoyant force on an object in a fluid is an upward force equal to the weight of the fluid that the object displaces.
An object is lowered into a
container of water.

7. When the object is completely
submerged, the weight of the
displaced fluid equals the buoyant
force acting on the object.

8. Substances that are denser than water will sink in water
Substances that are denser than water will sink in water. Given this, how does a steel ship float? The shape of the ship allows the ship to float. Imagine a ship that was just a big block of steel, as shown on the left in If you put that steel block into water, it would sink. But ships are built with a hollow shape. The amount of steel is the same, but the hollow shape decreases the ship’s density. Water is denser than the hollow ship, so the ship floats.