# Energy

Compared to the idea of a force....

• Energy is a more fundamental concept
• But more abstract:
• Batteries, stretched rubber bands, books on high shelves all have it

## Chicxulub impact

The asteroid or comet that hit the Yucatan probably...

• had diameter of ~ 10 km
• was moving ~20 km/s (bullet at speed of sound: ~0.3 km/s)
• hit so hard that the rock and water were instantaneously heated to a temperature hotter than the surface of the sun,
• Energy released was > than 10,000 $\times$ US + Soviet nuclear stockpiles ($10^8$ megatons of TNT equivalent).

### Energy is not an atom or element

Something has energy if...

• it has the ability to change itself or its environment,
• change = damage (sometimes)!
• or, it can do work, which is force $\times$ distance,
• it can be turned into heat (well, that's a kind of change in environment too).

Heat is energy that raises the temperature of matter.

We might include a tank of gasoline, a battery, water backed up behind a dam, a stretched out piece of elastic material, or a flying brick.

## Energy history of humankind

Plants develop photosynthesis

...They are able use solar energy falling on them to synthesize sugars, which can be burned later when the sun isn't shining.

### Animals

Animals come along that get their energy by eating the grass, or eating each other. Including our ancestors.

### Cooking

Our ancestors spent a good deal of time eating to get enough energy. but a lot of the energy we ate was used in breaking down the cell walls of raw plant matter. Cooking manages to do a lot of that breaking down for us. We can take in a lot more calories in a shorter period of time. And now they had...

### More time for other things

Ships are propelled by wind: air stirred up by heat (thermal energy) from the sun.

### Coal powers the industrial revolution

Coalbrookdale by night by Phillipp Jakob Loutherbourg

The foundry at Coalbrookdale was one of the first coke-fired furnaces. Coke was made from bituminous coal.

Coal (and oil) are the remains of plants and organic matter, containing a large amount of easy-to-extract energy--just light it!

The industrial revolution came about as people realized they could build machines and huge manufacturing processes based on burning fossil fuels - coal. Only the wealthy could afford to build such infrastructure, and benefitted from it the most, ushering in an era of Capitalism.

### Chocolate chips vs TNT

Gram for gram, which substance has more energy (per gram)--Chocolate chip cookies or TNT?

How to measure this energy??

 Calories (~ Watt $\cdot$ hours) Bullet (moving at speed of sound) 0.01 Battery (auto) 0.03 ThermalE in water 0.05 Battery (alkaline) 0.15 TNT (trinitrotoluene) 0.65 Modern explosive (PETN) 1 Chocolate chip cookies 5 Coal, or Ethanol (alcohol) 6 Butter 7 Gasoline 10 Natural gas (methane) 13 Hydrogen 26 Asteroid @ 30 km / s 100 Uranium 235 20 $\times 10^6$