Heat vs TemperatureHeat: The energy that transfers from one object to another because of a temperature difference between them.

a higher-temperature object to a lower-temperature object

Temperature: the measurement of how warm or cold something is compared to a standard (a scale).

It is proportional to the average kinetic energy of the molecules

Matter expands when its warm/ contracts when its cold.

Measuring Heat

calorie - the most common unit of heat

The amount of heat required to raise the temperature of 1 gram of water by 1 degree Celsius.

1000 calories = 1 kilocalorie The SI unit of heat and all forms of energy is joules 

1 calorie = 4.184 Joules

Thermal Expansion• Many substances expand when heated

– When heated, the particles (atoms or molecules) in a substance vibrate more. This means they need more space. So the substance expands

Heat

The particles in a substance do not expand themselves!

Particles are the same size

Expansion joints in bridges

Compensations for Thermal ExpansionCompensations for Thermal Expansion

Railways tracks are laid in sections with gaps between them. The railways sections are held together by fish-plateand fastened by bolts and nuts through oval holes.

gap rail track

oval hole for nut and bolt to slide along

Compensations for thermal expansion

Pipelines carry very hot gases (such as steam), therefore need expansion joint (in ring form) to avoid damages given by expansion.

ExpansionJoint

Contraction can be a problem too!

In summer and winter, the overhead power lines and telephone wires will expands and contracts due to thechanging weather.

Overhead power lines and telephone wires

Different materials expands by different amount when heated through the same increase in temperature.

Materials Increase in length (mm) per m

aluminium 0.25brass 0.19iron 0.12steel 0.11glass 0.09invar 0.01

Expansion of various Solids

Brass expands more than iron when hot, and contracts moretoo.

Ex. Thermostats, oven thermometers.

Bimetallic Strip A bimetallic strips is made up of two strips of different metals.

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.

Heat Transfer3 ways to transfer heat:

•Conduction

•Radiation

•Convection

Bill Nye Heat - http://www.youtube.com/watch?v=svqieBM2ijs

Conduction Conduction – transfer of heat by direct contact.

Conductors – materials that transfer heat well

Insulators – materials that delay the transfer of heat.

Why does metal feel colder than wood, if they are both at the same temperature?

Metal is a conductor, wood is an insulator. Metal conducts the heat away from your hands. Wood does not conduct the heat away from your hands as well as the metal, so the wood feels warmer than the metal.

ConvectionConvection = Heat is transferred by currents in a liquid or a gas. When heated

molecules move from one place to another, taking the heat with them.

Warm molecules rise and cool molecules sink

RadiationRadiation = transfer of heat by means of electromagnetic

waves

energy is carried by electromagnetic waves and does not involve the movement or the interaction of matter.

can occur through matter or through a vacuum. 

Four containers were placed equidistant from a heater. Which container would have the warmest water after ten minutes?

The __________ container would be the warmest after ten minutes because its surface absorbs heat _______ the best. The _________ container would be the coolest because it is the poorest at __________ heat radiation.

dull blackradiation

shiny metalabsorbing

Shiny metal

Dull metal

Dull black

Shiny black

Four containers were filled with warm water. Which container would have the warmest water after ten minutes?

Shiny metal

Dull metal

Dull black

Shiny black

The __________ container would be the warmest after ten minutes because its shiny surface reflects heat _______ back into the container so less is lost. The ________ container would be the coolest because it is the best at _______ heat radiation.

shiny metalradiation

dull blackemitting

1st Law of ThermodynamicsThe energy of the universe is constant.

Energy can be neither created nor destroyed, so while energy can be converted to another form, the total energy remains constant.

AKA Law of Conservation of Energy.

Energy In Energy Out

Any Isolated System

Heat added

30. If 10 J of energy is added to a system that does no external work, by how much will the internal energy of that system be raised? 10J

31. If 10J of energy is added to a system that does 4J of external work, by how much will the internal energy of that system be raised? 6J

 32. 100J of heat is added to a system that does 60J of external work. The internal energy change of the system is? 40J

= increase in internal energy

+ external work done by the system.

2nd Law of ThermodynamicsHeat will always flow from an object of higher temperature to an object of lower temperature

… or natural systems tend to proceed toward a state of greater disorder.

… aka entropy

EntropyA measure of the disorder of a system.

Systems tend to change from a state of low entropy to a state of higher entropy. That is to say, if left to themselves, systems tend to increase their entropy.

x

Solids Liquids Solutions Gases

Increasing Entropy

Fewer Particles More Particles