behavior of liquids and gases: diffusion and pressure
TRANSCRIPT
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Behavior of Liquids and Gases: Diffusion and Pressure
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Review: How do substances change state?
• How does a liquid change to a solid?– Freezing (freezing point temperature)
• How does a solid change to a liquid?– Melting (melting point temperature)
• How does a liquid change to a gas? (2)– Boiling (boiling point temperature)– Evaporation
• How does a gas change to a liquid?– Condensation
• What is the name for the process in which a solid changes to a gas or gases change to a solid?– Sublimation
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How do liquids and gases behave?
• Diffusion• Pascal’s principle• Archimedes’ principle
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Diffusion
• Diffusion is the mixing of particles– Movement of particles from an area of high
concentration to an area of low concentration• Why can we smell a fire even though we are
far away?– Particles in the gas state are far apart
and move freely to mix with the air • Many toxic gases are mixed with
chemicals so you can smell them and move to safety!
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Pressure and Pascal’s principle
• Pressure is force applied over a certain area– Pressure = force area- Unit of pressure is called a pascal (Pa)
• Pascal’s principle states that:If you apply pressure at any point in a confined substance, the pressure travels unchanged throughout the substance
• Example: if you squeeze toothpaste thatforce will move through the toothpaste and push it out of the hole in the tube
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Gas Pressure andPascal’s principle
• You may increase the pressure of a gas in a confined space by forcing more particles into the same amount of space
• Ex: inflating a balloon or a ball– Increasing the pressure by adding more
air particles to the space– What do you think would happen to the pressure
inside the ball if you inflated it inside a warm building then took it outside to a cold temperature?
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Behavior of Liquids and Gases: Archimedes’ principle
7SCIENCE
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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
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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
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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
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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)
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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)