ThermodynamicsEQ: How are temperature and thermal energy related?We will distinguish between temperature and thermal energyI will compare and contrast temperature and thermal energy with a venn diagram

https://www.youtube.com/watch?v=f1eAOygDP5s&list=PL1PVyahQ52MjRsaR_6Q9fJ23h5lWOfBkS

ThermodynamicsWhat 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 - QUnit – Joules (J)

ThermodynamicsWhat 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 - TUnit – 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 kg80ºF 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 (0oC) and boiling point (100oC) 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 + 273

Kelvin to Celsius C = K - 273

Temperature Conversions

• Example 1:What is the temperature in Fahrenheit if an object has a temperature of 135 C?⁰

Using F = 1.8C + 32 ̊F = 1.8(135) + 32 F = 243 + 32F = 275 F⁰

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

https://www.youtube.com/watch?v=WMYb5684Kp0

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:ConductionConvectionRadiation

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)

• 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

Radiation travels in straight linesTrue/False

Radiation can travel through a vacuum

True/FalseRadiation requires particles to

travelTrue/False

Radiation travels at the speed of light

True/False