Presentation on theme: "Law of Conservation of Energy"— Presentation transcript:
1 Law of Conservation of Energy States that energy can neither be created or destroyed or that the total amount of energy in a system remains constant.We can measure the energy in terms of calories.
2 CaloriesOne calorie is defined as the amount of energy needed to raise the temperature of 1 gram of water 1oCAbbreviated as (cal)Dietary calories (C) = 1000cal or 1kcal = amount of energy released from foods
3 Heat EnergyHeat - a flow of energy from a hot object (higher energy) to a cold object (lower energy). The most familiar form of energyAll matter contains some heat energy.The net energy transferred from or to an object as a result of a temperature difference which results in a change in internal energy
4 Review Heat EnergyThe heat energy of a substance is determined by how active its particles (atoms and molecules) are.A hot object is one whose atoms and molecules are excited and show rapid movement.A cooler object's molecules and atoms will be less excited and show less movement.
5 What is Heat Energy? As heat is added to an object the temp. increases The added heat becomes part of the object’s internal energy
6 Heat travels from a hot object (higher energy) to a cold object (lower energy). So how does heat travel from one object to another?By Convection, Conduction and Radiation.
7 Heat Transfer by Convection Convection occurs only in liquids and gases. We call liquids and gases fluids. It cannot happen in solids. It needs particles to be free to move about.A radiator in a room heats up the room by convection (NOT radiation).
8 Heat Transfer by Convection Look at the engine at the left.Water carries heat from a hot engine through a pump and delivers it to a radiator, whose duty is to give up heat to the air.
9 Heat Transfer by Conduction The process in which heat passes through a solid substance is called conduction. Metals are good conductors of heat. Non-metals are generally bad conductors of heat. Liquids and gases are bad conductors of heat as well. A bad conductor of heat is called an insulator.
10 Ability of a metal to conduct heat? What is an element of metal made of?Atoms that vibrateFree electrons that move aroundThey are constantly vibrating or oscillating against each other.Through these collisions, the heat energy is conducted
11 Heat Transfer by Conduction The flow of heat from a hot part of a body to a cooler part, without transfer of matter.Can also take place from one body to another, provided the two bodies are in contact, and a temperature difference exists between them.A pot on a hot plate is heated by conduction from the stovesurface, via the undersideof the pot.
12 Heat Transfer by Radiation The easiest way to explain heat transfer by RADIATION is by the heat we feel from the sun or a light bulb.RADIATION of heat is the transfer of heat energy through matter or space as electromagnetic waves.Examples :Electromagnetic waves called infra-red radiation that is emitted from earth.Ultraviolet radiation that is emitted from the sun and causes sunburnsMicrowaves that cook food
13 Review Heat flows from hot objects to cold objects. Heat flow depends on the temperature difference.Heat is not temperature.Heat passes by conduction, convection, or radiation.Radiation is caused by infra-red radiation
14 Determining the amount of heat gained or lost by a substance Step 1You will need the following formulas for your calculations:where T refers to the change in temperatureTf refers to the final temperature andTi refers to the initial temperature
15 Determining the amount of energy lost or gained Step 2where Qcal refers to the heat gained (or lost) expressed in caloriesmass of water is expressed in grams(1 mL water = 1 gram)T refers to the change in temperatureAnswers are expressed in calories or cal
16 45 gm sample of water is heated from 24.0ºC to 82.0 ºC How much heat was gained by the cold water?∆T = 82.0 – 24.0 = 58.0 ºCQcal = 45 g x 58.0 ºC = 2610 = 2600cal
17 If a sample of hot water and cold water are mixed together… Based on the Law of Conservation of Energy what would you expect?
18 110. 5 gm sample of hot water has an initial temp of 61. 8ºC. 250 110.5 gm sample of hot water has an initial temp of 61.8ºC gm of 1.8ºC water is added to it and the final temperature is 6.8ºC1 - How much heat was gained or lost by the by the cold water?2 - How much heat was gained or lost by the warm water?
19 How Do We Measure the Changes in Heat Energy? Temperature
20 What is Temperature?The measure of the average kinetic energy of the particles (atoms and molecules) of a substanceKinetic energy is the energy an object posses because of it’s motion
21 How do we measure temperature? With a thermometer.1. A thermometer is an instrument that utilizes the physical property of thermal expansion for the purpose of accurately determining temperature
22 What is thermal expansion? The property of a substance to expand with an increasing temperature andcontract with a decreasing temperatureThe expansion and contracting allows for the quantitative measure of temperature by using a thermometer.
23 Thermometer Most common is the bulb type As the substance gets hotter, the particles in the liquid mover faster and spread outThis causes the red liquid to move up.Gives us a quantitative reading.