Some basic concepts of energy for FYF 101?J Alternative Energy

Some basic concepts of energy for FYF 101?J Alternative Energy

Prepared for BIO/EES 105 Energy in our World Kenneth M. Klemow, Ph.D. Wilkes University Overview Energy defined Forms of energy The physical nature of energy Energy and Newtonian Laws of Motion

Units of measure Conversions Terminology pertaining to energy Ability to do work Physicists distinguish between kinetic and potential energy Energy comes in different forms Radiation

Mechanical energy Chemical energy Atomic energy Electromagnetic energy Electrical energy Heat energy Sir Isaac Newton 1642 - 1727 Energy Force = Force x distance = Acceleration x mass

Acceleration Speed = Speed / time = Distance / time Speed = distance / time Ways of expressing Miles / hour Km / hour

Feet / second Meters / second Other relationships Distance = Speed x time Time = Distance / speed Velocity is a vector: implies speed and direction 1 ft/s = 0.305 m/s

1 mi/h = 0.447 m/s 1 km/hr = 0.28 m/s 1. A car drives 72 miles in 120 minutes. What is its velocity in miles per hour? 2. A person runs at 6 miles per hour. How far can that person run in 10 minutes? Expressed in miles: Expressed in feet:

3. How long does it take for that person to run 528 feet? A car is traveling 60 miles per hour. How many feet can it travel in one second? Acceleration = Change in velocity / time Expressed as distance / time X time Or distance / time22

Occurs when an object is speeding up or slowing down Units include Miles / hour22 Km / hour22 Feet / second22 Meters / second22 1 ft/s22 = 0.305 m/s22 1 m/s22 = 3.28 ft/s22

A Kia Rio can accelerate to 30 km / hour in 6 seconds. What is its acceleration? Express in terms of m / second22 (see (see Example Example 2.2 2.2 on on p. p. 40) 40) Velocity = Acceleration X Time

Problem: Return to the Kia What What is velocity velocity after after 1 1 second? second?

After After 3 seconds? After After 6 seconds? After After 9 seconds? After After 12 seconds? Gravity has an acceleration (Agrav grav) Metric: 9.8 m/s22 English: 32 ft/s22

X = (1/2) x A x T22 (see (see p. p. 62 62 of of text text for for derivation) derivation) Problem: Imagine you drop a stone from a cliff, and it takes three seconds to hit the water below. How high was the cliff above the water? How fast was the stone moving when it hit the water?

Momentum = mass x velocity Force = mass x acceleration Common unit of measure for force: Newton (N = kg x m / s) Other relationships

Mass = Force / acceleration (kg=F/a) Acceleration = Force / mass (A=F/kg) A rock having a mass of 2 kg falls into the water from a cliff. What is the force that it exerts? Does that force vary if the cliff is 50 high, as opposed to being 100 high? Mass is a property of a body (measure of inertia). Irrespective of its position relative to gravity.

Often expressed as Kg. Weight depends on gravity. An object will weigh more on earth than on moon because gravitational force greater on earth. Weight often considered to be unit of force, expressed as Kg x Agrav grav Where Where Kg is mass mass and and A Agrav acceleration due due to

to grav is acceleration gravity. gravity. 1. A body will continue to remain at rest or in motion with a constant velocity unless it is acted upon by an outside force. 2. The acceleration of an object is directly proportional to the net force acting on it, and is inversely proportional to its mass (A = F/Kg). 3. For every action force, there is an equal and opposite reaction force.

Energy = Force x Distance Joule (J) = Newton x meter Energy Energy of an apple apple 1 1m m from from the the floor floor Some additional measures of energy

Foot Foot pound pound = = 1.4 1.4 JJ 1 calorie calorie = 4.187 J 1 BTU BTU = 1054 J Potential energy Stored

Stored energy, able to do do work work if released. released. Examples Examples include: include: Objects Objects placed placed at at an an elevation elevation Water Water behind behind dam dam Release

Release energy energy if if they they fall fall Objects Objects placed placed at at mechanical mechanical tension tension Wound Wound up up spring spring Release Release energy

energy if if tension tension is is relieved relieved Chemical Chemical bond bond energy energy Organic Organic molecules molecules Energy Energy released released if if combusted

combusted Potential Potential energy due due to elevation elevation PE PEGG = = weight weight xx height height = = Kg Kg xx A Agrav xh h grav x

Kinetic energy Energy of motion Examples include: Moving Moving water water Moving Moving catapult Can be expressed mathematically as 1/2 1/2 Kg Kg x v22

Rate at which energy is produced, used, or transferred. Expressed as energy per time Common units include Watt Watt (J (J / s) s) Ft-lb Ft-lb // sec sec Horsepower

Horsepower 1 1 hp hp = = 550 550 ft-lbs ft-lbs // sec sec 1 1 hp hp = = 746 746 Watts Watts

Question: A kilowatt hour is a measure of: Power Energy Force Acceleration None of the above Power = energy / time Energy = power x time www.belmont.k12.ca.us

W = (KE + PE) Both have two meanings Conversion Translating Translating between between different different units units of of measure measure Joule Joule <-> <-> Calorie

Calorie <-> <-> BTU BTU Changing Changing from from one one form form to to another another Chemical Chemical energy energy -> -> Thermal Thermal energy energy

Conservation First law of thermodynamics Energy Energy cannot cannot be be created created or or destroyed, destroyed, only only converted converted Reduce wasteful energy consumption

Switch Switch from from incandescent incandescent to to light-emitting light-emitting diode diode (LED) (LED) 1 kilowatt hour = 3.60 x 1066 J 1 barrel oil equivalent = 6.119 x 1099 J 1 ton wood equivalent = 9.83 x 1099 J

1 ton coal equivalent = 29.31 x 1099 J 1 ton oil equivalent = 41.87 x 1099 J 1 quad (PBtu) = 1.055 x 1018 18 J First law: Energy cannot be created nor destroyed, can only be converted (conservation of energy) In an isolated system, total energy will always remain constant

Second law: No energy conversion is perfect; always get some loss as heat. Gives direction to a reaction Get increase in disorder (entropy). In system involving movement, always get loss as friction Thus perpetual motion machines are impossible (yet people still try to invent them) Waste heat given off to environment

Ultimately go off to space Efficiency = energy (work) output X 100 total energy input Efficiencies can vary from 5% - 95% In multistep processes, efficiency is the product of efficiency of each step. Comparative assessments of energy processes / devices typically take great pains to accurately measure efficiency

Refer to Table 3.1 on p. 78 of text

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