Forces in fluids (liquids and gases)

Pressure

Force is related to pressure; BUT force is not equal to pressure.

Pressure = force/ area

Remember force is measured in Newtons (N)

Remember area is in square units (m2)

SI unit of pressure is the Pascal

1 Pascal = 1 Newton/ 1 square meter

1 Pa= N/ m2

All of the forces exerted by the individual molecules in a fluid add together to make up the pressure exerted by the fluid.

Fluid= a liquid or a gas

The more “stuff” over you the greater the pressure.

Water pressure increases as depth increases.

Air pressure decreases as elevation increases.

Remember weight is a force.

Air pressure (at sea level)

14.7 pounds per square in; 14.7 Lbs./ in2

10.13 N/ cm2

10.13 N/ cm2 = Pa

Buoyancy

The buoyant force acts in the upward direction, against gravity, so it makes the object feel lighter.

Since pressure is greater with depth, the buoyant force is greatest below the object. The net force is upward.

Weight vs. buoyant force

Archimedes’ principle:

The buoyant force on an object is equal to the weight of the fluid displaced by the object.

Buoyancy and Density

Density

Density = mass/ volume

Mass is measured in grams.

Volume is measured in ml or cm3

Density = grams/ ml or grams/ cm3

http://ippex.pppl.gov/interactive/matter/denslab.html

Pascal’s principle

When force is applied to a confined fluid (closed system), an increase in pressure is transmitted equally to all parts of the fluid.

Pressure at A= 500 N/ 1m2

Pressure at car= /20m2

500N/ 1m2 = ?/20m2

A little force/ small area =

A large force/ large area

Bernoulli’s principle

http://www.innerbody.com/htm/body.html

http://www.ims.uni-stuttgart.de/phonetik/EGG/page5a.htm

Density

Density = mass/ volume

Mass is measured in grams.

Volume is measured in ml or cm3

Density = grams/ ml or grams/ cm3

http://www.explorelearning.com/index.cfm?method=cResource.dspView&ResourceID=17