Thermodynamics EQ:  How are temperature and thermal energy related?  We will distinguish between temperature and thermal energy  I will compare and contrast temperature and thermal energy with a venn diagram aR_6Q9fJ23h5lWOfBkS

Thermodynamics What is thermal(heat) energy? Energy that is transferred from one body to another as a result of a difference in temperature. Microscopically: the measure of how many atoms there are in a substance multiplied by how much kinetic energy each atom possesses Variable - Q Unit – Joules (J)

Thermodynamics What is temperature? A measure of the hotness or coldness of an object Microscopically: related to how fast the atoms within a substance are moving. It determines which direction heat will flow Variable - T Unit – Celsius, Fahrenheit, Kelvin

Thermal Energy and Temperature Temperature depends only on the average kinetic energy of the particles in the object. Thermal energy of an object depends on both the temperature and the number of particles that make up the object. Thermodynamics 2 kg 80ºF 1 kg 80ºF The mass, of the left block is twice the amount of the right block, this means that is has twice the thermal energy Average kinetic energy of the particles in each block is the same, this means both object have the same temperature

the state in which the rate of energy flow between two objects is equal and the objects are at the same temperature, as shown on the right. What is thermal equilibrium? Thermodynamics

Heat Transfer Heat always moves from a warmer place to a cooler place. Hot objects in a cooler room will cool to room temperature. Cold objects in a warmer room will heat up to room temperature. Thermal Equilibrium Hot coals Cool water

Units for Measuring Temperature In the U.S., temperature is measured in degrees Fahrenheit… BUT NOT IN SCIENCE! The Celsius scale is based on the freezing point (0 o C) and boiling point (100 o C) of water. The Kelvin (or absolute) scale is based on the theoretical temperature at which all particle motion stops (Absolute Zero) A one-degree Celsius temperature change is equal to a one Kelvin temperature change

Temperature Conversions Fahrenheit to Celsius C = (F – 32 ̊ )/1.8 Celsius to Fahrenheit F = 1.8C + 32 ̊ Celsius to Kelvin K = C Kelvin to Celsius C = K - 273

Temperature Conversions Example 1:What is the temperature in Fahrenheit if an object has a temperature of 135 ⁰ C? Using F = 1.8C + 32 ̊ F = 1.8(135) + 32 F = F = 275 ⁰ F

Expansion/Contraction Why are gaps left in pavements, railway tracks, and floor boards? Why are electricity cables left slack? Why are bottles of minerals not filled up to the top? Because materials expand when they heat up we need to leave room for that.

Expansion V Contraction The reason materials expand when heated is because the heat gives the molecules energy and as a result they begin to move, leaving them further apart and hence the material expands Cooling has the opposite effect, the particles move closer together causing the molecules to contract One exception: water expands when cooled

Closing Task I will compare and contrast temperature and thermal energy

Heat transfer EQ: What are the methods of heat transfer? We will understand how heat energy move from one object to another I will identify the method of heat transfer given various scenarios

Heat transfer Heat transfers by three methods:  Conduction  Convection  Radiation

Conduction The process by which heat energy is transferred by adjacent molecular collisions inside a material. The medium itself does not move. Particles are in direct contact with each other.

Conduction When the metal is heated, this ‘sea of electrons’ gain kinetic energy and transfer it throughout the metal. Insulators, such as wood and plastic, do not have this ‘sea of electrons’ which is why they do not conduct heat as well as metals. thermal conductivity in metals occurs by the movement of free electrons

Conductors versus Insulators If a substance easily allows heat to move through it, we can say it is a good conductor of heat, example: most metals If a substance does not allow heat to pass through it easily we can say it is an Insulator, example: wood, plastic, glass Why do many saucepans have plastic handles? Conduction

Convection Hot water rises Cooler water sinks Convection current Cools at the surface

Convection What happens to the particles in a liquid or a gas when you heat them? The particles spread out and become less dense. Convection transfers heat through moving currents in gases or liquids

Radiation How does heat energy get from the Sun to the Earth? There are no particles between the Sun and the Earth so it CANNOT travel by conduction or by convection. ? RADIATION

Radiation Radiation is the transfer of heat by means of electromagnetic waves. Does not need a medium to travel (no molecules)electromagnetic waves To radiate means to send out or spread from a central location. All objects radiate energy in the form of electromagnetic waves Radiation can be absorbed or reflected Different materials absorb different amounts of radiation, as do different colors of materials. (it is better to wear light colors on a hot, sunny day than it is to wear dark colors) Snow caps, for example, reflect away more radiation than rock does. (shiny materials, light colors)

Radiation travels in straight lines True/False Radiation can travel through a vacuum True/False Radiation requires particles to travel True/False Radiation travels at the speed of light True/False