Thermal Physics

Thermal Physics

1. The Kinetic Theory of Matter

   • All matter is made up of atoms that are moving.
   • The motion from the atoms gives the object energy. Therefore kinetic energy is the energy of a particle due to its motion
     • Solids -> vibrating atoms Liquids -> flowing atoms Gases -> move freely Plasma -> move incredibly fast and freely
   • Higher temperature = faster the atoms are moving
   • How heat energy affects matter:

2. Heat vs. Thermal Energy vs. Temperature

   • Heat
     • Definition: The result of the movement of tiny particles (atoms/molecules/ions) in solids, liquids and gases.
       • Measures the energy transferred in Joules (J)
         • Heat always moves from a warmer place to a cooler place
           • Methods of Heat Transfer
             • Conduction: The process that moves energy from 1 object to another when they are touching physically
               • Conductors: materials that transfer energy easily
                 • Insulators: materials that don't transfer energy easily
             • Convection: When particles with more heat energy in a liquid or gas move & take the place of particles with less heat energy
               • *Density: the degree of compactness of a substance
             • Radiation: The transfer of heat energy in the form of electromagnetic waves. Unlike convection & conduction, radiation doesn't require particles to transfer heat
               • Dull dark surfaces are better emitters of infrared radiation than shiny light surfaces
   • Thermal Energy
     • Definition: The total energy contained within a system that is responsible for its temperature.. Therefore thermal energy=kinetic energy+potential energy
       • Measures the total energy of all particles in an object in Joules (J)
   • Temperature
     • Measures the average kinetic energy of all the particles in the object; in Celsius/Fahrenheit/Kelvin
       • The atoms' mass and speed determines the temperature of the object
         • Converting Celsius to Kelvin -> +273° Converting Kelvin to Celsius -> -273°
           • Water Boils: 373.15K = 100°C = 212°F
             • Water Freezes: 273.15K = O°C = 32°F
               • Absolute Zero: OK = -273.15°C = -459.67°F
                 • Absolute Zero is when atoms are frozen & have no random kinetic energy
                   • Kelvin is an absolute scale. Celsius is an arbitrary scale

3. Specific Heat Capacity

   • The amount of temperature increase depends on: 1. How much heat was added, 2. the size of the object, 3. the material of which the object is made
     • When you add the same amount of heat to the same mass of different substances, the amount of temperature increase is different. This is because each substance has a specific heat capacity - which is the amount of heat necessary to raise one mass unit of that substance by one temperature unit.
   • The amount of heat gained or lost by an object when its temperature changes can be calculated by the formula Q=mcΔt

4. The Law of Thermal Equilibrium/Zeroth Law of Thermodynamics

   • If 2 systems are separately in thermal equilibrium with a 3rd system, then those 2 are in thermal equilibrium with each other
   • Systems are in thermal equilibrium when they have the same temperature and hence the same kinetic energy
     • If 2 objects are in thermal contact, thermal energy will flow through the hot to cold object until they are at the same temperature and are at thermal equilibrium
   • Calorimetry is important because it is used to measure an amount of thermal energy. It determines the specific heat capacities and latent heats of different substances because of the conservation of energy

5. Mechanical Work & Efficiency

   • First Law of Thermodynamics
     • States that energy simply changes from 1 form to another and the total energy in a system is constant
       • Any change in the internal energy (ΔU) of a closed system = the amount of heat Q supplied to the system - the amount of work W done by the system on its surroundings
         • ΔU = Q - W
           • ΔU is positive if Q is added or W is done on the system. ΔU is negative if Q is removed or W is done by the system
   • Thermal energy has the capacity to do mechanical work
     • Work is done when energy is transformed and changes energy type
       • In any system with thermal energy, the thermal energy has the capacity to do mechanical work
   • Efficiency
     • Energy is conserved but sometimes transforms into non-useful energy
       • The energy efficiency is the percentage of useful work that is obtained from a process
         • Efficiency = (energy output/energy input) x 100%

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