Pressure is a force exerted over an area on the surfaceof an object.

Force and Pressure are not the same thing:Pressure decreases as the area over which a forceis applied increases.

Force Pressuregreater

ForcePressure less

Units of pressure are Newtons/meter2

1 N/m2 = 1 pascal (Pa)

ForceForce

When a force is applied to a confined fluid, the change in pressure is transmitted equally to all parts of the fluid.

Cartesian Diver

Pressure increasedPressure decreased

Fluid Particles

Pressure is caused by the movement of particles in the fluid. Every time they bump against the sideof the container they create pressure. The more bumpsthe more pressure.

Fluid Particles

The more particles, the more pressure. The faster the particles move, the more pressure.

Pressure caused by the weight of the air in the atmosphereas gravity pulls it down toward the center of the earth.

Pressure caused by the weight of water as gravity pulls it down toward the center of the earth.

Remember, weight is a force.

Air and water pressures press on objects from every direction.

If the pressure becomes unbalanced, the pressure of airor water can crush an object.

The air pressure inside balances the air pressure outside the container.

But if we take the air out of the container, the outside pressure will be far greater than inside and crush the can.

As your elevation increases, atmospheric pressure decreases.

Water pressure increases as depth increases.

The force in liquids that acts opposite to gravity—itcauses objects to feel lighter.

Objects sink if their weight is greater than the buoyantforce acting on them.

The buoyant force acting on a submerged object is equal to the weight of the fluid the object displaces.

The buoyant force acting on theobject

equals the weight of the water displacedby the object.

Weight

Buoyant Force

Weight

Buoyant Force

Density = Mass Volume

If the density of an object is less than the density of water, the object will float.

If the density of an object is greater than the density of water,the object will sink.

ForceForce

When a force is applied to a confined fluid, the change in pressure is transmitted equally to all parts of the fluid.

10N Force

1m2 area

Pressure of 10N/m2

100N Force

10m2 area

Pressure = 10N 1m2

Force = 10N/m2 x 10m2

How much pressure is produced by a 150N force actingover an area of 3m2?

A 5N force is applied to a 5m2 piston in a hydraulic device.If the second piston has an area of 25m2, what is the forceproduced by this second piston?

Pressure Force Area

? 300N 20m2

15N/m2 ? 15m2

3,000N/m2 150N ?

? 750N 7.5m2

The faster a fluid moves

the less pressure the fluid exerts.

As the speed of a moving fluid increases, the pressure within the fluid decreases.

Moving streamof wind (fluid)

Lower Pressure

Smoke moves up chimney from high to low pressure.

Wings are shaped so that air movesfaster over the top of the wing than under the wing. This causes lower pressureabove the wing than below and creates lift so the plane can fly.