October 2014

How is Energy Related to Work?  Energy – the ability to do work.  When work is done to an object, energy is transferred to that object.  Work -- the transfer of energy.  Since energy is the ability to do work, it is also measured in the same unit as work which is Joules (J).

What are the differences between Kinetic and Potential Energy?  KINETIC ENERGY: Energy of motion  Depends on mass & velocity KE = ½ mv 2  Examples: Water flowing over a dam Car rolling down a hill

What are the differences between Kinetic and Potential Energy?  POTENTIAL ENERGY: Stored energy  Depends on: mass height  Examples: Water stored behind a dam Car sitting on top of a hill

What are the differences between Kinetic and Potential Energy?  Label W-Z as KE or PE

What is happening at each point on the pendulum in terms of KE and PE?

Types of Energy  Elastic Potential Energy: energy stored due to an objects shape (stretched or compressed)  Chemical Potential Energy: Energy stored in chemical bonds  Gravitational Potential energy: energy stored due to objects position in a gravitational field.  Mechanical Energy: energy associated with motion and position of everyday objects

Types of Energy  Thermal Energy: Total potential and kinetic energy of all particles in an object  Electric Energy: energy of electric charges  Electromagnetic: changing electric and magnetic fields (radiation etc.)  Nuclear Energy: energy stored in atomic nucli

How and why is energy transferred from one form to another?  Energy can be changed from one form to another. Changes in the form of energy are called energy conversions.

How and why is energy transferred from one form to another? Examples  Green plants convert the sun’s energy (electromagnetic) into starches and sugars (chemical energy).  In an electric motor, electric energy is converted to mechanical energy.  In a battery, chemical energy is converted into electric energy.  Wood burning converts chemical energy into heat and light energy.  In an automobile engine, burned fuel is converted from chemical energy into mechanical energy.  The most common energy conversion is the conversion between potential and kinetic energy.

Energy Transformations

Energy Transformations- Draw and label 3 energy conversions

What is the Law of Conservation of Energy?  When E changes from one form to another, the total E remains unchanged.  Law of conservation of energy – energy is neither created nor destroyed, it can only change form.

THERMAL ENERGY  Amount of thermal energy depends on Mass Temperature Phase of matter  Thermal Expansion: “most” matter expands as it is heated and contracts when cooled (Particles move farther apart as Temp ↑)  Heat: Transfer of thermal energy from one object to another  Flows from HOT → COLD

Types of Thermal Energy Transfer  1. Conduction: particles touch and transfer E from one object to another (slowest in gases because particles are far apart and fastest in solids because particles are already touching ) Conductor: allows E to move easily Insulator: does NOT allow E to move easily  Examples of Conduction: Touching a hot iron Having a plastic handle on a pot

Types of Thermal Energy Transfer  2. Convection: Thermal E transfers as particles move due to a difference in temperature (density) Hot risesCold sinks (less dense)(denser)   Often referred to as the “bulk” movement of particles  Examples: Ovens Fans  Natural cycles: Weather Ocean currents Plate tectonics

Types of Thermal Energy Transfer  3. Radiation: transfer of energy by waves  Does NOT require matter/particles to move ---can move through empty space (vacuum) (all objects radiate thermal E, as Temp↑, rate of radiation↑)  Examples x-rays tanning beds

Conduction vs. Convection vs. Radiation

How are the 3 thermal energies applied?

Specific Heat  Specific Heat: the amount of heat needed to raise the temperature of 1g of material 1 ﹾ C (low specific heat = temp rises quickly as E is added) (high specific heat = temp rises slowly as E is added)  Heat = mass  specific heat  change in temperature  Q = mcΔT  *ΔT = T f -T i (Final Temperature – Initial Temperature)   C (specific heat) is usually found on a table or chart…except when you are asked to calculate for C. Q ΔTcm

Which one will take the most/ least amount of time to heat up?