Kenneth M. Klemow, Ph.D.Wilkes University

Prepared for BIO/EES 105

Energy in our World

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

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

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 Newton1642 - 1727

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

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 mph = 0.447 m/s 1 km/hr – 0.28 m/s

1 ft/s = 0.305 m/s 1 mph = 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?

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?

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 / time2

Occurs when an object is speeding up or slowing down

Units include◦ Miles / hour2

◦ Km / hour2

◦ Feet / second2

◦ Meters / second2

Acceleration = Change in velocity / time◦ Expressed as distance / time X time◦ Or distance / time2

Occurs when an object is speeding up or slowing down

Units include◦ Miles / hour2

◦ Km / hour2

◦ Feet / second2

◦ Meters / second2

1 ft/s2 = 0.305 m/s2

1m/s2 = 3.28 ft/s2

1 ft/s2 = 0.305 m/s2

1m/s2 = 3.28 ft/s2

A Kia Rio can accelerate to 30 km / hour in 6 seconds. What is its acceleration?◦ Express in terms of km / hour2

◦ Express in terms of m / second2

A Kia Rio can accelerate to 30 km / hour in 6 seconds. What is its acceleration?◦ Express in terms of km / hour2

◦ Express in terms of m / second2

Velocity = Acceleration X Time

Problem:◦ Return to the Kia

What is velocity after 1 second? After 3 seconds? After 6 seconds? After 9 seconds? After 12 seconds?

Velocity = Acceleration X Time

Problem:◦ Return to the Kia

What is velocity after 1 second? After 3 seconds? After 6 seconds? After 9 seconds? After 12 seconds?

Gravity has an acceleration◦ Metric: 9.8 m/s2

◦ English: 32 ft/s2

Gravity has an acceleration◦ Metric: 9.8 m/s2

◦ English: 32 ft/s2

X = (1/2) x A x T2 (see p. 62 of text for 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?

X = (1/2) x A x T2 (see p. 62 of text for 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 / s²)

Other relationships◦ Mass = Force / acceleration (m=F/a)◦ Acceleration = Force / mass (A=F/m)

Momentum = mass x velocity

Force = mass x acceleration

Common unit of measure for force:◦ Newton (N = kg x m / s²)

Other relationships◦ Mass = Force / acceleration (m=F/a)◦ Acceleration = Force / mass (A=F/m)

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?

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 m x g (or mg) Where m is mass an g is acceleration due to gravity.

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 m x g (or mg) Where m is mass an g is acceleration due to 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/m).

3. For every action force, there is an equal and opposite reaction force.

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/m).

3. For every action force, there is an equal and opposite reaction force.

Energy = Force x Distance ◦ Joule (J) = Newton x meter

Energy of an apple 1 m from the floor◦ Some additional measures of energy

Foot pound = 1.4 J 1 calorie = 4.187 J 1 BTU = 1054 J

Energy = Force x Distance ◦ Joule (J) = Newton x meter

Energy of an apple 1 m from the floor◦ Some additional measures of energy

Foot pound = 1.4 J 1 calorie = 4.187 J 1 BTU = 1054 J

Potential energy◦ Stored energy, able to do work if released. Examples

include: Objects placed at an elevation

Water behind dam Release energy if they fall

Objects placed at mechanical tension Wound up spring Release energy if tension is relieved

Chemical bond energy Organic molecules Energy released if combusted

◦ Potential energy due to elevation PEG = weight X height = mgh

Potential energy◦ Stored energy, able to do work if released. Examples

include: Objects placed at an elevation

Water behind dam Release energy if they fall

Objects placed at mechanical tension Wound up spring Release energy if tension is relieved

Chemical bond energy Organic molecules Energy released if combusted

◦ Potential energy due to elevation PEG = weight X height = mgh

Kinetic energy◦ Energy of motion

Examples include: Moving water Moving catapult

◦ Can be expressed mathematically as 1/2 m v2

Kinetic energy◦ Energy of motion

Examples include: Moving water Moving catapult

◦ Can be expressed mathematically as 1/2 m v2

Rate at which energy is produced, used, or transferred.◦ Expressed as energy per time◦ Common units include

Watt (J / s) Ft-lb / sec Horsepower

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

Rate at which energy is produced, used, or transferred.◦ Expressed as energy per time◦ Common units include

Watt (J / s) Ft-lb / sec Horsepower

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

That unit is a measure of:◦ Power◦ Energy◦ Force◦ Acceleration◦ None of the above

That unit is a measure of:◦ Power◦ Energy◦ Force◦ Acceleration◦ None of the above

Power = energy / time Energy = power x time

Power = energy / time Energy = power x time

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W = (KE + PE) W = (KE + PE)

Both have two meanings◦ Conversion

Translating between different units of measure Joule <-> Calorie <-> BTU

Changing from one form to another Chemical energy -> Thermal energy

◦ Conservation First law of thermodynamics

Energy cannot be created or destroyed, only converted

Reduce wasteful energy consumption Switch from incandescent to light-emitting diode

(LED)

Both have two meanings◦ Conversion

Translating between different units of measure Joule <-> Calorie <-> BTU

Changing from one form to another Chemical energy -> Thermal energy

◦ Conservation First law of thermodynamics

Energy cannot be created or destroyed, only converted

Reduce wasteful energy consumption Switch from incandescent to light-emitting diode

(LED)

1 kilowatt hour = 3.60 x 106 J 1 barrel oil equivalent = 6.119 x 109 J 1 ton wood equivalent = 9.83 x 109 J 1 ton coal equivalent = 29.31 x 109 J 1 ton oil equivalent = 41.87 x 109 J 1 quad (PBtu) = 1.055 x 1018 J

1 kilowatt hour = 3.60 x 106 J 1 barrel oil equivalent = 6.119 x 109 J 1 ton wood equivalent = 9.83 x 109 J 1 ton coal equivalent = 29.31 x 109 J 1 ton oil equivalent = 41.87 x 109 J 1 quad (PBtu) = 1.055 x 1018 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).

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

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

energy (work) output energy (work) output

total energy input total energy input X 100X 100EfficiencyEfficiency

• 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

• 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 Refer to Table 3.1 on p. 78 of text

Based on kinetic energy of molecules◦ Heat is TOTAL energy of all molecules in a system

Typically measured in Calories or BTUs◦ Temperature is AVERAGE energy of all molecules

in a system Typically measured in degrees

Fahrenheit Celsius Kelvin

Water freezes 32 0 273

Water boils 212 100 373

Human body 98.6 37 310

Within a system◦ Increase in heat causes increase in temperature

Between systems◦ Not related◦ One system can have higher heat yet lower

temperature Ocean vs duck

Heat can move from one system to another◦ Only when there is a temperature difference◦ Move from higher temperature to lower

temperature object.

Within a system◦ Increase in heat causes increase in temperature

Between systems◦ Not related◦ One system can have higher heat yet lower

temperature Ocean vs duck

Heat can move from one system to another◦ Only when there is a temperature difference◦ Move from higher temperature to lower

temperature object.

Measure of change in temperature as a result of heat absorbed.◦ Metric system: # joules needed to raise 1 kg of

material by 1 oC.◦ English system: # BTUs needed to raise 1 lb of

material by 1oF.

Measure of change in temperature as a result of heat absorbed.◦ Metric system: # joules needed to raise 1 kg of

material by 1 oC.◦ English system: # BTUs needed to raise 1 lb of

material by 1oF.

Represent phase changes◦ Vaporization: liquid <-> gas◦ Fusion: solid <-> liquid

Can represent large values◦ For water

Vaporization: 540 kcal/ kg Fusion: 80 kcal / kg

Heat absorbed or released depending on direction

Important in heat balance at earth’s surface, regulating temperatures of organisms

Represent phase changes◦ Vaporization: liquid <-> gas◦ Fusion: solid <-> liquid

Can represent large values◦ For water

Vaporization: 540 kcal/ kg Fusion: 80 kcal / kg

Heat absorbed or released depending on direction

Important in heat balance at earth’s surface, regulating temperatures of organisms

Conduction Convection Radiation

Conduction Convection Radiation

Renewable vs nonrenewable Traditional vs new energy Commercialized vs non-commercialized Centralized vs distributed generation On-grid vs off-grid

Renewable vs nonrenewable Traditional vs new energy Commercialized vs non-commercialized Centralized vs distributed generation On-grid vs off-grid

Primary energy is the energy as it is available in the natural environment, i.e. the primary source of energy.

Secondary energy is the energy ready for transport or transmission.

Final energy is the energy which the consumer buys or receives.

Useful energy is the energy which is an input in an end-use application.

Primary energy is the energy as it is available in the natural environment, i.e. the primary source of energy.

Secondary energy is the energy ready for transport or transmission.

Final energy is the energy which the consumer buys or receives.

Useful energy is the energy which is an input in an end-use application.

energy technology examples

Primary coal, wood, hydro, dung, oil

Conversion power plant, kiln, refinery, digester

Secondary refined oil, electricity, biogas

Transport/transmission

trucks, pipes, wires

Final diesel oil, charcoal, electricity, biogas

Conversion motors, heaters, stoves

Useful shaft power, heat

CO2H2O C6H12O6

Carbon reduction

Energy

Energy

Carbon oxidation