Molecules and Motion The motion of molecules produces

Molecules and Motion • The motion of molecules produces heat • The more motion, the more heat is generated

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.

Forms of heat transfer • Three forms of heat transfer: • Conduction • Convection • Radiation

Conduction • Conduction involves the transfer of heat through direct contact • Heat conductors conduct heat well, insulators do not

Conduction When you heat a metal strip at one end, the heat travels to the other end. As you heat the metal, the particles vibrate, these vibrations make the adjacent particles vibrate, and so on, the vibrations are passed along the metal and so is the heat. We call this? Conduction

Metals are different When the metal is heated, this The outer e______ lectrons of metal atoms ‘sea of electrons’ drift, and are free to move. gain kinetic energy and transfer it throughout the metal. Insulators, such as wood and paper, do not have this ‘sea of electrons’ which is why they do not conduct heat as well as metals.

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.

Convection • Takes place in liquids and gases as molecules move in currents • Heat rises and cold settles to the bottom

Convection What happens to the particles in a liquid or a gas when you heat them? The particles spread out and become less dense. What A liquid is or a fluid? gas. This effects fluid movement.

Fluid movement Cooler, more d____, ense fluids sink through w_____, armer less dense fluids. In effect, Cooler ink liquids and gases s___, warmer liquids and gases ise up. r___

Water movement Cooler water sinks Cools at the surfac e Convection current Hot water rises

Why is it windy at the seaside?

Radiation • Heat is transferred through space • Energy from the sun being transferred to the Earth

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

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

Emission experiment Four containers were filled with warm water. Which container would have the warmest water after ten minutes? Dull metal Shiny black Dull black shiny metal container would be the warmest after ten The _____ radiationback minutes because its shiny surface reflects heat _______ dull black container into the container so less is lost. The ____ emitting heat would be the coolest because it is the best at _______ radiation.

Absorption experiment Four containers were placed equidistant from a heater. Which container would have the warmest water after ten minutes? Dull metal Shiny black Dull black The _____ dull blackcontainer would be the warmest after ten radiation the best. minutes because its surface absorbs heat _______ shiny metal container would be the coolest because it is The _____ the poorest at _____ absorbing heat radiation.

Convection questions Why does hot air rise and cold air sink? Cool air is more dense than warm air, so the cool air ‘falls through’ the warm air. Why are boilers placed beneath hot water tanks in people’s homes? Hot water rises. So when the boiler heats the water, and the hot water rises, the water tank is filled with hot water.

Radiation questions Why are houses painted white in hot countries? White reflects heat radiation and keeps the house cooler. Why are shiny foil blankets wrapped around marathon runners at the end of a race? The shiny metal reflects the heat radiation from the runner back in, this stops the runner getting cold.

What type of heat transfer is involved? • Heating a room with a fireplace • Egg cooking in a frying pan • Roof of a house becoming hot

What type of heat transfer? • Warm air mass bringing a change in the weather • Wire getting hot from an electric appliance

Temperature and Heat • Kinetic energy is the energy of motion • Temperature is the measure of the average kinetic energy of an object

Question • How is kinetic energy related to heat production?

Thermometer • A instrument used to measure temperature • Thermometers commonly have alcohol (with dye) or mercury • Digital thermometers have replaced older ones

Celsius Scale • Celsius is the metric scale for measuring temperature • Water freezes at 0ºC and boils at 100ºC

Kelvin scale • The Kelvin scale is a metric temperature scale measured in Kelvin units (K) • Formula (273+ºC)= Kelvin

Absolute zero • The temperature in which all molecular motion stops (0 K)

Questions • Describe absolute zero. • What is absolute zero on the Celsius scale?

Measuring Heat • Increase in temperature • Addition of heat • A decrease in temperature • Removal of heat

Calories • Unit for measuring heat • The amount of heat needed to raise 1 gram of water one degree Celsius

Temperature • Joule is another unit for measuring heat • Mass and type of substance determine the amount of temperature change

Specific Heat • The ability of a substance to absorb heat energy (specific heat) • Different substances absorb heat at different rates • The greater the mass of the object the more heat is absorbed

What is a calorimeter? • Device used to measure the heat given off during chemical reactions

Heat and Phase Changes • A phase change is a physical change that requires a change in heat energy • Addition or removal of HEAT

Heat expansion • The expansion of a substance due to heat • Most solids, liquids, and gases expand as they are heated

Expansion of water • Between 4ºC and 0ºC, water EXPANDS as it cools and turns into a solid

Thermostat • A thermostat is a device that controls the temperature • The switch of a thermostat is a bimetallic strip

Bimetallic Strip • Two different metals that are bound together • They expand at different rates when heated • Used as a switch in a thermostat

Internal energy • The energy within a substance

1. Which of the following is not a method of heat transfer? A. Radiation B. Insulation C. Conduction D. Convection

2. In which of the following are the particles closest together? A. Solid B. Liquid C. Gas D. Fluid

3. How does heat energy reach the Earth from the Sun? A. Radiation B. Conduction C. Convection D. Insulation

4. Which is the best surface for reflecting heat radiation? A. Shiny white B. Dull white C. Shiny black D. Dull black

5. Which is the best surface for absorbing heat radiation? A. Shiny white B. Dull white C. Shiny black D. Dull black