Behavior of Liquids and Gases: Diffusion and Pressure

1. Behavior of Liquids and Gases: Diffusion and Pressure

2. 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

3. How do liquids and gases behave? • Diffusion • Pascal’s principle • Archimedes’ principle

4. 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!

5. 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

6. 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?

7. Behavior of Liquids and Gases: Archimedes’ principle 7SCIENCE

8. 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

9. 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

10. Density and Archimedes’ principle Why 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

11. 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)

12. 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)