Thermal Energy Concept 3 Notes PDF

 Thermal Energy Thermal Energy: the sum of kinetic and potential energy of the particles in an object. – Thermal energy increases as mass increases. – Thermal Energy increases as temperature increases. Temperature: a measure of the average kinetic energy of particles i...

 Thermal Energy Thermal Energy: the sum of kinetic and potential energy of the particles in an object. – Thermal energy increases as mass increases. – Thermal Energy increases as temperature increases. Temperature: a measure of the average kinetic energy of particles in an object. – The higher the temperature, the faster the particles are moving.  Thermal Energy How do you know if someone has been sitting in your chair? Thermal energy always flows from higher temperature objects to lower temperature objects. Heat: (Q) the transfer of energy from one object to another. – Measured in Joules. Transfer of Thermal Energy No such thing as “cold” – When you feel cold, you are simply feeling the absence of heat. Example: Explain what happens when you hold a cold drink and your hand starts to feel “cold”. When heat When heat flows into flows out of an object, an object, the change the change in heat is + in heat is - Transfer of Thermal Energy Can be transferred 3 ways. 1. Conduction: transfer of energy through matter by direct contact of particles. – Solids are best conductors of heat. Particles are already so close together so contact is easy. Transfer of Thermal Energy Can be transferred 3 ways. 2. Convection: transfer of energy by the movement of heated particles. – Occurs in liquids and gases. Currents move heat from warmer to cooler parts of the substance. Transfer of Thermal Energy Can be transferred 3 ways. 3. Radiation: transfer of energy through electromagnetic waves. – Occurs fastest in gases. – Can be absorbed or reflected. Can travel through space and between molecules.  Materials Some materials transfer heat well, and others do not. Conductors: Insulators: materials that materials that do allow heat to flow not allow heat to easily flow easily – Ex. Air, wood, – Ex. Metals and skin Styrofoam, plastic, fiberglass  Specific Heat Specific Heat: the amount of heat needed to raise the temperature of 1 kg of a material by 1 °C or K. – Specific to different types of materials. – Measured by a calorimeter. Q = mcΔT Q = change in thermal energy (or heat) Measured in J m = mass Measured in kg c = specific heat Measured in J/kg °C ΔT = change in temperature (Tf – Ti) Measured in °C  Example #1 A wooden block has a mass of 20 kg and a specific heat of 1,700 J/(kg oC). Find the change in thermal energy of the block as it warms from 15 oC to 25 oC. m = 20.0 kg Q = (20)(1700)(25-15) C = 1700 J/(kg oC) Ti = 15 oC Q = (20)(1700)(10) Tf = 25 oC Q=? Q = 340,000 J Q = mcΔT Q = mc(Tf – Ti)  Practice Time 1. The air in a living room has a mass of 60 kg and a specific heat of 1,020 J/kg oC. What is the change in thermal energy of the air when it warms from 20 oC to 25 oC? Answer: Q = 306,000 J 2. The thermal energy of water in a mug increases by 12,552 J when the water is heated from 20 oC to 40 oC. If the specific heat of water is 4,184 J/kg oC, what is the mass of the water? Answer: m = 0.15 kg