Topic 8: Energy & the Price We Pay

Dr. George Lapennas

Department of Biology

What is Energy?

Short answer: Energy is the ability to do Work.

What is Work?

Work is done when a Force acts through a Distance in the direction of the Force

Work = Force x Distance

Are these guys doing Work?

Is this guy doing Work?

Now has this guy done Work?

Power = Work / Time

= (Force x Distance)/Time

= Force x (Distance/Time)

= Force x Velocity

Power = Work / Time

1 “horsepower” =

550 foot-pounds/second

Power = Work / Time

1 “horsepower” =

550 foot-pounds/second

4 Fundamental forms of Energy:

1 Potential Energy (PE)

2 Kinetic Energy (KE)

3 Electro-Magnetic Energy (E-M)

4 Mass Energy

1 Potential Energy (PE) = “energy of position”

Energy gained by pulling something away from an attractive force

or

Energy gained by pushing something toward a repulsive force

1 Potential Energy (PE) = “energy of position”

Gravitational PE = work done to lift something against attraction of gravity

Gravitational PE gained = weight x height lifted = mg x h

1 Potential Energy (PE) = “energy of position”

Elastic PE = stretching a spring or a rubber band or compressing a spring or a gas or bending a springy bow

1 Potential Energy (PE) = “energy of position”

Electrical PE = pulling + away from –

pushing + toward + or – toward –

1 Potential Energy (PE) = “energy of position”

Electrical PE = pulling + away from –

pushing + toward + or – toward –

1 Potential Energy (PE) = “energy of position”

Magnetic PE

Chemical Potential Energy

Work done against Friction does not yield Potential Energy

4 Fundamental forms of Energy:

2 Kinetic Energy = “energy of motion”

3 Electro-Magnetic Energy = light, ultraviolet, x-rays, radio waves, micro-waves

3 Electro-Magnetic Energy = light, ultraviolet, x-rays, radio waves, micro-waves

3 Electro-Magnetic Energy = light, ultraviolet, x-rays, radio waves, micro-waves

3 Electro-Magnetic Energy = light, ultraviolet, x-rays, radio waves, micro-waves

4 Mass Energy = energy derived from mass

4 Mass Energy = energy derived from mass

4 Mass Energy = energy derived from mass

4 Mass Energy = energy derived from mass

Internal energy

First Law of Thermodynamics

“Conservation of Energy”

Energy can neither be created nor destroyed

The amount of Energy in an “isolated system” is constant over time

An isolated system is one where neither matter nor energy can cross between the system and the surroundings.

The whole universe itself is an isolated system, as there are no surroundings to exchange matter or energy with.

An isolated system is one where neither matter nor energy can cross between the system and the surroundings.

The whole universe itself is an isolated system, as there are no surroundings to exchange matter or energy with.

Energy can be transferred (moved) from one place to another

and

Transformed from one form to another

Internal energy

A closed system is one where energy can cross the boundary, but matter cannot.

The internal energy of a closed system changes with heat transfer and work done

Energy transformation from one form to another

Energy transformation from one form to another

Pile driver

Energy transformation from one form to another

Pile driver

Energy transformation from one form to another

Pile driver

Energy transformation from one form to another

Pile driver

Energy transformation from one form to another

Pile driver

Energy transformation from one form to another

Energy transformation from one form to another

Energy transformation from one form to another

Energy transformation from one form to another

Energy transformation from one form to another

Energy transformation from one form to another

Energy transformation from one form to another

Second Law of Thermodynamics

The Entropy of the Universe can only increase (or stay the same) over time.

It cannot ever decrease.

Entropy = disorder = randomness

Second Law of Thermodynamics

The Entropy of the Universe can only increase (or stay the same) over time.

It cannot ever decrease.

Entropy = disorder = randomness

All “changes” that can actually occur result in an increase in the Entropy of the Universe

Entropy is “Time’s Arrow” which points in the direction of “spontaneous” changes = changes that can happen

Entropy is “Times Arrow”

Entropy is “Times Arrow”

Second Law of Thermodynamics - Examples

TemperatureTemperature- a measure of the average kinetic energy of the

molecules making up a substance.

HeatHeat- energy of molecules that is gained/lost through a temperature

difference.

Second Law of Thermodynamics - Examples

Second Law of Thermodynamics - Examples

PE-KE-Elastic E-KE-PE-KE- Elastic E-KE-PE-Elastic E …

Entropy

Every actual change results in some energy becoming unavailable for doing work

There are no perfect heat engines

There are no perfect heat engines

The End