Notes – Pressure & Buoyant Force Chapter 3, Lesson 2

Pressure in a Fluid A fluid is a material that can flow and has no definite shape. Liquids and gases are fluids. Fluids can exert forces.

Pressure in a Fluid Pressure is the force per unit of area applied on the surface of an object. Pressure depends on the area over which a force is exerted. If the area increases, pressure decreases.

Pressure in a Fluid Pressure depends on the size of the force. If the force increases, pressure increases.

Pressure in a Fluid The equation for pressure is: P = F ÷ A Pressure (pascals) = force (newtons) area (meters squared) The SI unit of pressure is the pascal, abbreviated Pa. A pressure of 1 Pa is equal to a force of 1 N applied over an area of 1 m2 1 Pa = 1 N / m2

Pressure in a Fluid For any liquid in a container of any shape, the pressure depends only on the height of the column of liquid above the surface where you measure the pressure.

Pressure in a Fluid The deeper underwater you go, the greater the pressure is on you. This is because as you go deeper, the column of water above you gets taller.

Pressure in a Fluid In a fluid, pressure is exerted on all points on the outside of an object in a direction perpendicular to the surface of the object at that point.

Pressure in a Fluid A gas, like any fluid, exerts a pressure on an object. That pressure depends on the height of the gas above the object.

Pressure in a Fluid Atmospheric pressure is the force exerted per unit area by air particles. As you climb, or increase your elevation, atmospheric pressure decreases.

Pressure in a Fluid Atmospheric pressure at sea level is caused by a large weight of gas, but is difficult to notice because there is an equal, internal pressure pushing out from the inside of your body.

Buoyant Force The buoyant force is the net upward force exerted on an object in a fluid by the surrounding fluid. It acts against gravity.

Buoyant Force In a fluid, there is no net horizontal force on an object caused by pressure from the fluid.

Buoyant Force Because in a fluid, pressure increases with depth, the force of the fluid pushing up on the bottom of an object is always greater than the force of the fluid pushing down on the top of the same object.

Buoyant Force The size of the buoyant force does not depend on depth.

Buoyant Force Archimedes’ Principle states that the buoyant force on an object is equal to the weight of the fluid the object displaces.

Pressure is the ____ per unit area. A mass B volume C force D pascal 3.2 Pressure and the Buoyant Forces Pressure is the ____ per unit area. A mass B volume C force D pascal

Which direction does the buoyancy force act on an object? A upward 3.2 Pressure and the Buoyant Forces Which direction does the buoyancy force act on an object? A upward B downward C to the left of the object D to the right of the object

Where is the pressure the greatest on an object in a fluid? A top 3.2 Pressure and the Buoyant Forces Where is the pressure the greatest on an object in a fluid? A top B bottom C sides D none of the above

Vocab – Pressure & Buoyant Force TB p. 140-148 force fluid pressure atmospheric pressure buoyant force Archimedes’ principle