CHAPTER 4

Energy Kinetic E – energy in the form of motion Units are joules KE (J) = 1/2m (kg) x v (m/s) ^2

Potential Energy Potential E – stored energy due to position Three types of potential energy: 1. Elastic potential energy 2. Chemical potential energy 3. Gravitational potential energy

Gravitational Potential Energy GPE = mass x gravity x height GPE (J) = m (kg) x 9.8 m/s^2 x h (m) A 0.06kg ball starts to fall from a height of 2.9m. How much gravitational potential energy does the ball have at that height?

Form of energy can convert back and forth between the potential and kinetic Ex: pendulum Law of conservation of E – energy cannot be created nor destroyed, only the form changes

Fission vs. Fusion Nuclear fission – breaking apart of nuclei, which releases energy Nuclear fusion – 2 H nuclei fuse together to form a He nucleus, which also releases a large amount of energy Ex: how the sun heats the earth

Ch 6.1, 6.2, & 16.1

Temperature Molecules are atoms held together by chemical bonds Temperature is the average kinetic energy of the atoms/molecules Temp is measured in Kelvin

Thermal Energy The sum of the kinetic and potential energy of the molecules is thermal E If you increase the temp, the thermal E increases If you increase the mass, the thermal E increases

Heat Heat is the thermal E that flows from high temp to low temp Measured in Joules

Specific Heat The amount of heat needed to raise the temperature 1 degree (C or K) Error in chart on pg 161 Water J/kg K Water’s high spec heat lets it absorb a lot of E without changing temp Alcohol J/kg K Measured using a calorimeter

Calculating Thermal Energy Q= Thermal Energy in Joules (J) m= mass C= specific heat T= temperature (final-initial) Q=mC<>T

Calculate the thermal energy when an iron rod heats from 20 degrees C to 60 degrees C.

Transfer of Thermal Eenrgy Conduction- direct contact (solids) Convection- motion of heated particles (liquids and gases) Ex: convection currents in air or water Radiation- electromagnetic waves (can occur in a vacuum) Ex: outer space

Insulators Insulators don’t allow heat to flow through it easily Good insulators are poor conductors Examples of good insulators: Wood, plastic, fiberglass, air

Kinetic Theory 1. All matter is composed of small particles. 2. These particles are in constant, random motion. 3. These particles are colliding with each other and the walls of their container.

Particle Organization Solid state- particles are closely packed together in a specific arrangement Liquid state- particles farther apart and moving more freely Gas state- particles in constant random motion and fill the container (diffusion) Plasma state- gas with charged particles (common in outer space)

Changing state Melting- going from solid to liquid Heat of fusion- amt of E required for melting to occur Evaporation- going from liquid to gas Heat of vaporization- amt of E required for evaporation to occur

Thermal Expansion Expansion in solids when temp increases Ex: baking bread Expansion in liquids Ex: mercury in thermometer Expansion in gases Ex: Hot air balloons

Exceptions to the rule Water does the opposite as other solids Usually when solids freeze, they contract But when water is frozen, it expands! Amorphous solids don’t have a definite temperature in which they change from solid to liquid Ex: glass and plastic