Behavior of Liquids and Gases: Archimedes’ principle

7SCIENCE Wed. April 13

Review: What are some factors that affect the behavior of liquids and gases?

• Diffusion- mixing of particles

• Pressure - Pascal’s principle– When pressure is applied to a point in

a liquid or gas the pressure will travel unchanged through the liquid or gas

Density and Archimedes’ principle• Every substance (solid, liquid or gas) has a density• Density refers to if particles in a substance are closely

packed together Density (g/mL)= mass (g)

volume (mL)

Higher density = particles are packed more closely

Lower density = particles are further apart

Density and Archimedes’ principleWhy do some objects float and others sink?

• If an object has a density lower than that of the surrounding liquid or gas, it will float

• OPPOSITE: If an object has a density higher than that of the liquid or gas, it will sink

Buoyancy and Archimedes’ principle• The idea of buoyancy is that objects tend

to float or sink in a liquid

• Buoyancy is a decrease in weight caused by an upward force in a liquid or gas

- Objects have a specific buoyancy

– Ex: floating in a swimming pool or lake

Archimedes’ principle states:An object will sink until the volume of liquid displaced equals the weight of the object (then it will float)

Application of Archimedes’ principle“Plimsoll line”- Line painted on the side of a ship or boat- If the boat is sitting low and the line is under the

water, the ship is overloaded (too heavy)