Behavior of Liquids and Gases: Diffusion and Pressure

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

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

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!

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 that force will move through the toothpaste and push it out of the hole in the tube

Gas Pressure and Pascal’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?

Behavior of Liquids and Gases: Archimedes’ principle 7SCIENCE

Review: What are some factors that affect the behavior of liquids and gases? Diffusion - mixing of particlesmixing 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’ 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

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)