THE ABILITY TO CAUSE CHANGE 1

mechanical energy 2 T y p e s o f E n e r g y Radiant energy

types of energy oToThermal energy - from the motion of molecules oCoChemical Energy – mostly among chemical bonds oNoNuclear energy - from the nuclei of an atoms oEoElectrical and Magnetic energies – E&M interactions oRoRadiant energy -- carried by electromagnetic waves oMoMechanical energy – usually by large bodies 3

Energy Energy is the capacity (ability) to do work. Kinetic Energy: Associated with an object in motion Potential Energy: Is the interaction energy of an object wit another 4 CLIP

Foundations of Engineering Chapter 22

Accounting for Energy - Part 1 Chapter 22

RAT 1 Turn off your monitors, close your books and notes.

RAT 1 As an INDIVIDUAL, you have 3 minutes to answer the following questions: A) Name three types of work B) Name two types of potential energy C) Name two types of kinetic energy

Objectives Understand what energy is Understand path energies Work (specific classification; see next) mechanical, shaft, hydraulic, electrical, photon… Heat conduction blackbody radiation

What is energy? Let’s define in the most general way Work first Work is a change in the universe Energy – is the source or driving force able to perform such a work Thus, work done on x changes the x energy

Energy Make an analogy for energy: money is a “unit of exchange”, Example 1 car = $20 k 1 house = $100 k 5 cars = 1 house =

Energy Equivalents 1 kg coal = 42,000,000 joules 1 kg uranium = 82,000,000,000,000 joules (82x10 12 ) 1 kg uranium = 2,000,000 kg coal!!

Energy is a conserved quantity Generally, energy is a conserved quantity, i.e., generation and consumption are zero. In fusion and fission systems, energy can be generated (reactors, sun, stars, radioactive atoms, … In particle accelerators, energy can be consumed, also everywhere in the universe cosmic rays became particles These are not common engineering systems For most applications: Accumulation = Net Input

Types of Energy Accumulation = Net Input State Energies Kinetic Potential Internal (Independent of Path) Path Energies Work Heat (Depend on Path)

Path Energies Work is an energy flow across a boundary from a driving force mechanical + shaft + hydraulic + electrical + chemical + laser Heat is an energy flow resulting from a temperature driving force. conduction + blackbody radiation

Mechanical Work Results from a force applied over a linear distance

Shaft Work Results from a twisting force (torque, T) applied over a circular distance θ

Pairs Exercise #1 A lawn mower engine is started by pulling a cord wrapped around a sheave. The radius of the sheave is 8.0 cm and the cord is wrapped around the sheave twice. If a constant force of 90 N is applied to the cord, what work is done?

Shaft Power Power = work/time Units are usually horsepower (hp)

Pairs Exercise #2 How much power (in hp) is produced if your automobile engine is producing 250 ft-lb of torque at 4000 rpm?

Hydraulic Work xx P1P1 P2P2 F Q = V/t (flow rate) W = F  x F = A(P 2 -P 1 ) W = A(P 2 -P 1 )  x Volume of fluid that flows: V=A  x W = V (P 2 -P 1 ) W = Qt (P 2 -P 1 ) A (area of piston face)

Pairs Exercise #3 Atmospheric-pressure water is pumped at rate of 15 gal/min into a 60-psig storage tank. A) How much work (in ft-lb) is done by the pump in one day assuming it pumps constantly for the 24-h period? B) What “size” pump (i.e., power requirements in hp) is required for this job?

Electrical Work In electricity, the driving force is a voltage potential difference. Electrons move from lower to higher potential; i.e., they flow uphill, just opposite to positive charges The force required to move a charge, q, a distance  x from voltage V 1 to V 2 is F = q(V 2 -V 1 )/  x

Electrical Work Current [Amperes] is charge/time, thus i = q/t, or q = it Therefore electrical work is:

Pairs Exercise #4 You buy a light bulb that uses A (current) for your porch light (110 V). You leave your light on all weekend (48 hours). The electric company charges you 5.75 cents per kW-h (kilowatt-hour). How much does it cost to leave your light on all weekend?

Lasers and Photons LASER: Light Amplification by Stimulated Emission of Radiation The energy (E) of a photon (quantum of light) with frequency is E = h  Joules  = c/ E = hc  Joules h = Planck’s constant = 6.62 x J s c = speed of light = 3.0 x 10 8 m/s

Heat Heat is energy flow driven by temperature differences Two major types of heat flow: Conduction Blackbody radiation

Conduction Conduction equation A x Q/t k T2T2 T1T1 k = thermal conductivity Rate of heat conduction

Pairs Exercise #5 A 4-cm-thick insulator (k=2x10 -4 cal cm/(s cm 2 o C) has an area of 1000 cm 2. If the temperature on one side is 170 o C and the temperature on the other side is 50 o C, what is the heat transfer by conduction?

Black Body and Blackbody Radiation A black body adsorbs all incident electro- magnetic radiation, regardless of frequency or angle of incidence.electro- magnetic radiation A black body in thermal equilibrium (that is, at a constant temperature) emits electromagnetic radiation called black-body radiation with a spectrum that is determined by the temperature alone, not by the body's shape or composition.thermal equilibriumblack-body radiation spectrum temperature Heat transfer between blackbodies: