6.P.3 Energy Transfer and Interactions of Matter and Energy
Question If a cup of hot coffee and a red popsicle were left on the table in this room what would happen to them? Why? The cup of coffee will cool until it reaches room temperature. The popsicle will melt and then the liquid will warm to room temperature.
In this lesson you will revisit: The way in which heat behaves. The energy transfer methods: – conduction – convection – radiation How to reduce heat losses from your home.
Let’s Review: Let’s Review: Measuring Heat Heat is measured with a thermometer. Celsius Freezing: 0° Boiling: 100 ° Fahrenheit Freezing: 32 ° Boiling: 212 °
What Does Heating or Cooling Do to Materials? Melting: Solid matter changes its state to liquid. Freezing: Opposite process of melting is called freezing. Liquid matter loses heat and changes its state to solid. Boiling: Liquid matters gain heat and change their states to gas.
Energy can be transferred from one system to another in different ways: Thermally: when a warmer object is in contact with a cooler one Mechanically: when two objects push or pull on each other over a distance Electrically: when electrical source such as a battery or generator is connected in a complete circuit to an electrical device Electromagnetic Waves
Molecules in Motion: Thermal energy The motion of molecules produces heat The more motion, the more heat is generated Thermal energy is transferred through a material by the collisions of atoms within the material.
Heat Transfer The movement of heat from a warmer object to a cooler one. Heat flows through materials or across space from warm objects to cooler objects, until both objects are at equilibrium (balanced).
Heat Transfer Heat always moves Heat always moves from a warmer place to a cooler place. Hot objects in a cooler room will cool to room temperature after the hot object transfers some of their heat to the cold object. Cold objects in a warmer room will heat up to room temperature.
Heat Transfer Cont. Therefore warm things lose heat and cool things gain heat until they are all at the same temperature. Example: Ice cube is put in a glass of warm water. Ice cube gains heat from the water and the warm water loses some heat. Eventually the ice will melt and the water will be at an even temperature
Heat Transfer Methods Heat Transfer Methods A warmer object can warm a cooler object by contact (close/touching) or at a distance (far away) Conduction Convection Radiation www.teachersdomain.org/asset/lsps07_int_he attransfer/
Conduction Conduction involves the transfer of heat through direct contact Heat travels through solids primarily by conduction. Over time, thermal energy tends to spread through a material and from one material to another if they are in contact (conduction)
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 and so on, the vibrations are passed along the metal and so is the heat. We call this? Conduction
Convection Takes place in liquids and gases as molecules move in currents Heat rises and cool settles to the bottom. It continues in an up and down movement: warm rising and cool sinking (currents). These currents are in air, water, and other fluids
Water movement Hot water rises Cooler water sinks Convection current Cools at the surface
Cold air sinks Where is the freezer compartment put in a fridge? Freezer compartment It is put at the top, because cool air sinks, so it cools the food on the way down. It is warmer at the bottom, so this warmer air rises and a convection current is set up.
Convection questions 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. 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.
Radiation Radiation is energy that travels across distances in the form of electromagnetic waves. Heat is transferred through space Energy from the sun being transferred to the Earth Light and other electromagnetic waves can warm objects. How much an object’s temperature increases depends on: – how intense the light striking the surface – how long the light shines on the object – how much light is absorbed.
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 The sun is a major source of energy for changes on the earth’s surface. The sun loses energy by emitting (releasing) light. A tiny fraction of the light reaches the earth, transferring energy from the sun to the earth. The sun’s energy arrives as light with a range of waves: – Infrared Light: longer wave – Visible Light: visible wave – Ultraviolet Light: shorter wave
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
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.