[SOUND] Hi, my name is Tom Murphy.

I'm a professor in the physics department at UC-San Diego, and today we're

going to talk about energy past, present, future,

with a particular emphasis on the numbers.

And when it comes to numbers, I advocate a real flexibility with numbers, and

rounding and just sort of a, a

loose manipulation, because math is a lot easier.

If you don't take numbers so seriously and some people laugh when I

say that, but it's, it's really true that math is easier, division is

easier, multiplication is easier if you

can manipulate the numbers into something that

you can do in your head, then you can quickly understand the scale.

Have a problem rather something can work or

not work without getting bugged on the details.

So, for the instance the number pi and three are virtually the same thing.

And ten over three and square root of ten, all about the same.

So, you can simplify a lot of otherwise

complicated math, just by being flexible and so.

For instance, you can round a year to 30 million seconds.

You don't need to know that it's 31.55 million to do something useful.

Likewise, the US population is something like 300 million people.

Forget the fact that it might be 308 one year and 310 the next, whatever.

It's about 300 so, for example, the US uses

something like 20 million barrels of oil per day.

Now, if you have 300 million people using

20 million barrels of oil per day, that's a

pretty simple division problem and you come up

with 15 days per person per barrel of oil.

So a person goes through a barrel of oil in about 15 days.

And so, if you think about having a barrel

of oil delivered to your house once every 15 days.

That's somewhat staggering and puts things in perspective.

But oil is only about a third of our total energy demand.

So you can scale that again simple math, now it's five days

to go through the equivalent energy contained in one barrel of oil.

So how much energy is that?

Well depends on what units you like.

Whether you like, gigajoules or joules or BTUs or [UNKNOWN] all are units of energy.

But, you know, comes out to six,

gigajoules, 6,000,000,000 joules, 6,000,000 BTUs, 1,700 kilowatt-hours.

And this is a very important point, if

you divide energy by time, that's called power.

And the units for power are watts.

So if you take one watt is one joule per second.

So if you take six gigajoules, and divide by how many seconds are in

five days, you end up with about 10,000 joules per second, or 10,000 watts.

That's a rate at which we go through energy.

That's not watts per second.

That's already a rate And that's a 24 seven

constant draw of power that each American is responsible for.

Now, we'll come back to putting that in perspective.

And for now, I just want to point out.

If you take 10,000 watts or ten Kilowatts, multiply it

by 24 hours, you get 240 kilowatt hours per day.

So, 240 kilowatt hours, that's now an

energy cause it's a power, ten kilowatts times

a time, in hours, so, that's how many energy units we use per day as Americans.

So, just to put 10,000 watts into perspective.

Imagine two clothes dryers running full time.

They run at about 5,000 watts.

Or, you could have, pick your appliance,

hairdryers microwave ovens, toaster ovens, space heaters.

They all run at about 1,700 watts and that's actually not a coincidence.

That's because household circuits are usually rated at 15

or 20 amps and so they're kind of maxing out.

What a typical outlet can handle.

So they're all about 1700 watts, you need about

six of those running full time to make 10,000 watts.

Here's an interesting one, a human that can, who consumes about 2,000 calories

per day that turns out 2,000 calories is a unit of power per day.

Sorry, 2,000 calories is a unit of energy.

Per day that turns into watts, and it turns out to be 100 watts.

So a human runs at about 100 watts.

You need 100 humans to make 10,000 watts.

That's basically saying that we have 100 energy slaves working for us in America to

do the things that we need to get done, so that's quite a work force.