HEAT
Activity 1. Rub your hands quickly against each other. 2. Then quickly place them onto your face. 3. Describe what you feel. Your hands feel warm. 4. Why does it feel warm? It feels warm as HEAT has been generated when we rubbed our hands together.
Heat is a form of energy. Our main source of HEAT on earth is the SUN. Some HEAT sources are also sources of LIGHT. Eg. The Light Bulb, It gives off both Heat & Light. Temperature is the measure of how hot or cold an object is. HEAT What are some sources of Heat? What are some Heat sources that are also Light sources? Natural Sources Electrical Appliances Burning fuels like Volcanoes Geysers Lava from inside the Earth. Electric Iron Light Bulb Rice Cooker Hair Dryer Wood Gas Charcoal Candle Wax Petrol
Temperature is the measure of how hot or cold an object is. An object that has a HIGH temperature feels. hot An object that has a LOW temperature feels. cold Temperature The common units for temperature is degree Celsius. O C Thermometers are used to give an accurate reading of temperature. Thermometers come in many different types for different uses. For eg. 1. Laboratory Thermometers 2. Digital Thermometers 3. Pyrometers
Laboratory Thermometers Laboratory thermometers are used in the lab to conduct experiments. Are normally filled with mercury or alcohol. The temperature is shown by the marking on the thermometer which is nearest to the mercury level.
Digital Thermometers Pyrometers Used to measure very high temperatures.
Differences HEAT 1. Is a form of energy. Temperature 1. Is a measure of how hot or cold an object is. 2. Cannot be measured with a thermometer. 2. Can be measured with a thermometer.
Heat Flows and Changes in Temperature What would happen to the can of Coke after it is placed in the basin for a while? The Coke can will slowly warm up until it is the same temperature as the water in the basin. Cold can of Coke This is because it has gained heat from the warm water. Basin filled with Warm Water Heat will always flow from the hotter object to the colder object, until both reach the same temperature.
Basin filled with crushed Ice. Glass beaker filled with hot coffee. What would happen to the coffee in the beaker after it is placed in the basin for a while? Can you draw the arrows to show the flow of heat? The coffee will slowly cool down until it is the same temperature as the ice in the basin. This is as the coffee has lost heat to the ice.
When objects GAIN heat, they: Increase in temperature. Catch fire. Change from solid to liquid. Eg. Ice melting. Change from liquid to gas. Eg. Water boiling or evaporating. Expand (Get Bigger, Increase in SIZE). Boiling Water Beaker Bunsen Burner Ice Cube When objects Lose heat, they: Decrease in temperature. Change from gas to liquid. Eg. Condensation. Change from liquid to solid. Eg. Water freezing to form ice. Contract (Get smaller, Decrease in SIZE).
Good and bad conductors of Heat. (1) Take a look at the experiment setup at the top of the page in your Text Pg 129. Which of the candles will fall off first? Which will fall last? What has happened: Heat has been conducted from the flame to the candles through the metal rod. The candle that receives the conducted heat first will start to melt first.
Good and bad conductors of Heat (2). Take a look at the experiment setup in your Text Pg 130. Which of the toothpicks will fall off first? Which was the best conductor of heat? What has happened: The metal rod is the best conductor of Heat, it conducts heat fastest, so Toothpick A will be the fastest to drop. Air is the worst conductor, it conducts heat slowest, so Toothpick C will drop last.
Some examples of Good & Bad conductors. Steel Good Conductors Copper Iron Tin Aluminium Bad Conductors Plastic Wood Clay Glass
Frying Pan Material? Steel Material? Plastic The handle of the frying pan is made of plastic as plastic is a poor conductor of heat. This means that we can hold on to the handle while we are cooking.