What is energy?

Chain of energy

Newton’s Laws

1. An object in motion will stay in motion (or rest at rest) unless acted on by an outside force. (Inertia)

2. Force = mass x acceleration (Units: Newtons = kg x m/s2)

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

Work

Energy = ability to do work

Work = force exerted over a distance

W (or “energy”) = F x d

1 Joule = 1 Newton x 1 meter

4.18 Joule = 1.00 calorie

Power

Rate at which work is done

Power = Work / time

Watts = Joules / seconds

SO… Energy can also be expressed this way:

Energy = Power x time

Joules = Watts x seconds

Consider:

What does it mean to give electrical appliances a rating in watts?

What is a kilowatt? What is a killowatt-hour?

Why do we describe food in terms or calories?

Forms of Energy

Kinetic energy = Energy of moving objects

KE = ½ mass x velocity2

KE = ½ mv2

Joules = ½ kg x (m/s)2

Potential energy = Energy stored due to position or composition

PE = mass x acceleration due to gravity x height

PE = mgh

Joules = kg x m/s2 x m

Consider:

How do each of the following represent KE?

Heat radiating from a car

The sound of my voice

Muscles contracting

Light traveling to your eye

Consider:

How do each of the following represent potential energy?

A book on the edge of a table

A slice of pizza

Two magnets near each other

An electrical outlet

A stretched rubber band

What is heat?

Kinetic energy caused by atoms moving and colliding

Flows from warm body to cold body

Measured as temperature

Temperature Scales

° F = (1.8 x ° C) + 32

° C = (° F – 32) / 1.8

Both use freezing and boiling points of water as standards

Kelvin = ° C + 273

0 K = absolute zero

Specific Heat

Ability of a material to absorb/lose heat

Q = mcΔt

Heat gained/lost = mass x specific heat x change in temp

If two substances have equal mass and equal change in temp., what does the amount of heat gained depend on?

Heat transfer

Conduction – transfer due to atoms colliding or vibrating

Convection – transfer due to bulk movement of a fluid (gas or liquid)

Radiation – transfer due to electromagnetic radiations (uses electrical/magnetic fields instead of matter)

file:///Users/johnb/Desktop/lsps07_int_heattransfer/lsps07_int_heattransfer.html

How can these types of transfer work together?

1st Law of Thermodynamics:Conservation of Energy

Energy cannot be created or destroyed but can be transformed

PE = KE

mgh = ½ mv2

How can our examples of PE be converted into KE? Is the reverse also true?

Are energy conversions 100% efficient?

2nd Law of Thermodynamics: Entropy

Statements:

1. Heat will not flow spontaneously from a cold to a hot body.

2. You cannot construct an engine that does nothing but convert heat to useful work.

3. Every isolated system becomes more disordered with time. (Entropy)

http://www.stolaf.edu/people/giannini/flashanimat/transport/diffusion.swf

Applications

What is a gradient? How do they work? What kinds of gradients exist?

Can any system transfer energy with 100% efficiency? What does this mean in living systems?

How do we maintain order in systems (especially living systems)?

Where does energy go? Is it truly “lost”?

Back to the Sun – Nuclear Fusion

High pressure and high temperature force atoms together

Mass converted to energy

Energy radiates into space

How do atoms relate to energy?