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

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

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

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”

Second Law of Thermodynamics - Examples

Temperature Temperature- a measure of the average kinetic energy of the molecules making up a substance. Heat Heat- energy of molecules that is gained/lost through a temperature difference.

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

The End