Molecular Motion

Chapter 3

Matter and Energy

Matter- anything that has mass and volume• 4 states: solids, liquids, gases, plasma Energy- ability to do work:• Potential• Kinetic

Kinetic Molecular Theory

Kinetic Molecular Theory (KMT):• All matter is made of constantly moving

particles (atoms, molecules)• All particles have kinetic energy (KE)

Temperature and Kinetic Energy

Temperature• measure of average kinetic energy• the more KE an object has, the higher its

temperatureThermal energy= total KE; depends on:• particle speed- faster particles have more KE • number of particles- more particles have

greater thermal energy

Energy and SolidsSolids• low KE - particles vibrate but can’t move

around• definite shape, volume: *crystalline - repeating geometric pattern *amorphous - no pattern (e.g. glass, wax)

Energy and LiquidsLiquids• higher KE - particles can move, but are still

close together• indefinite shape, not volume• flows-fluid

Energy and GasesGases• high KE – particles move freely• indefinite shape and volume• flows- fluid

Energy and PlasmaPlasma• very high KE- particles collide with enough

energy to ionize (break into charged particles)• lacks definite shape or volume• can conduct electric current (unlike gases)• most common state of matter

States of Matter

Matter Shape VolumeSolids Definite DefiniteLiquids Not definite DefiniteGases Not definite Not definite

Changes of States Requiring Energy

(Remember: heated particles move faster; cool particles move slower

• Melting point- solid to liquid• Evaporation- liquid to gas• Sublimation- solids to gas

Changes of State Releasing Energy

• Condensation- gas to liquid• Freezing- liquid to solid• Temperature is constant during all changes in

state of matter (ex: If energy is added to ice, the temperature

of ice will not rise until all the ice has melted)

Conservation of Matter and Energy

• Neither mass nor energy can be created or destroyed during changes of state

Pressure and Fluids• Fluids: (liquids, gases) exert pressure

evenly in all directions• Pressure: amount of force exerted on a

given surface Pressure = force area• Pascal (Pa): unit of pressure; 1N/m²

Buoyant Force

• Buoyant force: the ability of a fluid to exert an upward force on an object immersed in it

(forces pushing up > forces pushing down)

* bouyant force > weight object rises ** bouyant force < weight object sinks ***bouyant force = weight object floats

Buoyancy and Density

• Density: = mass ÷ volume; D= m v• An object with D less than 1 g/cm³ will float

Archimedes Principle

• Archimedes principle: the bouyant force on an object in a fluid is equal to the weight of fluid displaced by the object

Pascal’s Principle

• Pascal’s Principle: a change in pressure at any point in an enclosed fluid will be transmitted equally to all parts of the fluid

F₁ = F₂ A₁ A₂

Pascal’s Principle

• Hydraulic devices: use liquid to transmit pressure from one point to another

ex: hydraulic breaks in cars, movement in starfish

Pascal’s Principle Practice

• A car weighing 1000 N sits on a 250 m2 platform. What force is needed on the 10 m2 plunger to keep the car from sinking?

Given:Platform:F= 1000A= 250m²Plunger:F= ?A= 10m²

Remember: F₁ = F₂ A₁ A₂

Solve:1000 N= F₂ 250m² 10m²

(1000N)(10m²)=(250m²)F₂

F₂ = 40N

Bernoulli’s Principle

• Bernoulli’s Principle: as the velocity of a fluid increases, the pressure exerted by the fluid decreases

Bernoulli’s Principle

• Viscosity: a fluid’s resistance to flow (usually, the stronger the attraction between particles in a liquid, the slower it flows)

Bernoulli’s Principle

• Venturi Effect: fluids flow faster through narrow spaces causing reduced pressure