TEMPERATURE AND THERMAL ENERGY Thermal energy – a form of kinetic energy characterized by randomness of motion at the atomic and molecular level Temperature – the degree or intensity of heat present in a substance or object; the measure of the hotness or coldness of a body
Heat – the energy transit from a body of higher temperature to one of lower temperature, under the influence of the variation in temperature; quantity of thermal energy absorbed or given off by a body.
LET’S DO THIS! Materials : 1 beaker half filled with hot water 1 beaker filled with hot water up to the brim 2 ice cubes Stopwatch Procedure : Drop the cubes to the individual beakers See what happens (Observe the rate by which the ice cube melts)
QUESTIONS… 1. Which of the 2 beakers has thermal energy? 2. Which of the 2 beakers has greater temperature? 3. Which of the 2 beakers contains more heat?
ANSWERS… 1. Both fluids inside the beaker have thermal energy. 2. Both have the same temperature. 3. The beaker filled with hot water up to the brim contains greater heat.
MEASURING TEMPERATURE 1. Using the tactile sense 2. Using a thermometer PARTS OF A THERMOMETER a. Thermal sensor b. Calibrations ~ °F, °C, or K
TEMPERATURE SCALES <ul><li>Fahrenheit Scale – (named after Ger. physicist Gabriel Daniel Fahrenheit ) based on the freezing and boiling point of water at normal atmospheric pressure ~ 32 ºF - freezing pt. and 212ºF – boiling pt. </li></ul>2. Celsius Scale – (named after Swed. astronomer Anders C. Celsius ) based on the freezing and boiling point of water at normal atmospheric pressure ~ 0 ºC - freezing pt. and 100ºC – boiling pt.
3. Kelvin Scale – (named after Brit. physicist William T. Kelvin ) erased the arbitrary assigned reference points, thus called not a relative scale but an Absolute temperature scale . 0 = nothing – Absolute Zero ~ lowest temperature possible, occurring when all random motion of molecules has ceased. In this scale: 273K – freezing pt. of water; 373K – boiling pt.
CONVERSIONS <ul><li>From °F to °C </li></ul><ul><li> (°F -32)5/9 </li></ul><ul><li>From °C to °F </li></ul><ul><li>(°C · 9/5) + 32 </li></ul><ul><li>From °C to K </li></ul><ul><li>°C + 273 </li></ul><ul><li>From °F to K </li></ul><ul><li>(°F-32)5/9 + 273 </li></ul>
THERMAL EXPANSION It is easier to open a tight bottle cap by exposing it to heat! EXPANSION OF MATERIALS “ Materials expand as their thermal energy increases.” -> Thermal expansion
“ Materials contract as their thermal energy decreases.” EXPANSION OF MATERIALS UNDER 100 °C 3.0 mm Aluminum 2.0 mm Brass 1.0 mm Steel 1.0 mm Concrete 0.9 mm Glass 0.9 mm Platinum alloy 0.3 mm Pyrex 0.1 mm Invar (alloy of Fe and Ni) Length of Expansion Materials (1 m in length)
“ Modern bridges are usually constructed with: a. One end attached while the other end rests on rollers b. With tooth like seams called, expansion joints
THERMOSTAT “ The amount of expansion of a material depends on the change in temperature.” The device that regulates the temperature of a material is called, a thermostat. It is usually consists of bimetallic strips e.g. Brass (alloy of Cu and Zn ) and Fe that are welded together. When the Brass side is heated it expands and contracts when cooled -> can help turn on/off a device such as heaters .
HEAT TRANSFER The study of the flow of heat within an object or from one medium to another due to their variation in temperature. <ul><li>Radiation - energy is emitted in the form of electromagnetic waves or subatomic particles e.g. </li></ul><ul><li>heat/warmth felt from a flame or bonfire sans touching it, the heat from the microwave oven and the heat from the sun. </li></ul>METHODS OF HEAT TRANSFER
2. Conduction - heat energy transfer caused by direct contact wherein heat travels from one molecule to another. For example, exposing metal to a flame, allowing an article to rest on a warm or hot object. “ Heat flows from a region of high concentration to a region of low concentration.” Hot -> Cold Legend:
3. Convection - transference of mass or heat within a fluid caused by the tendency of warmer and less dense material to rise producing air or fluid currents. Hot air rises Air cools down, becomes dense Cold air sinks Air heats up and becomes less dense
SPECIFIC HEAT The amount of energy required to raise the temperature of one kilogram (1 kg) of a substance by one °C (1°C) or one Kelvin (1 K). It is expressed in terms of Joules per kilogram-Kelvin (J/kg·K) or Joules per kilogram degree Celsius (J/kg·°C) or calorie per gram degree Celcius (cal/g·°C) in which 1 cal = 4.186 J.
THERMAL CAPACITY The amount of heat required to raise the temperature of a substance by 1 degree (1 °) and is the product of its mass and specific heat. Δ Q = mC Δ T Wherein, Δ Q is change in heat expressed in terms of J m is the mass of the substance in kg C is the specific heat in J/kg·K Δ T is the change in heat in K
WORD PROBLEMS 1. How much heat is needed to raise the temperature of 150 kg of water to 323 K? 2. What is the temperature of the mixture of 0.75 kg of water at 98 °C is added to 0.5kg of water at 25°C in a polystyrene cup?