Let's talk about some of the basic ideas
of Statics. So, Statics in general.  Is that helpful?
Statics in general: First of all, let's talk about the difference between statics and dynamics.
So statics is basically stuff
that doesn't move like static friction, right?
You use coefficient of static
friction with something's that's not moving.
It's not really that it's not moving,
it's that it's not accelerating.
So, you know how the idea is like if I'm at a constant speed, it's like I could be
still the whole world could be moving at
a constant speed or whatever? As long as
something is not accelerating, then it's
considered to be static. But in general,
when we talk about statics, we mean like
a...you know, table - it's not moving.
Statics would be something like that. Dynamics,
which is a whole other exciting class,
has bodies in acceleration. So bodies
accelerating. So, like a rocket. Like that. Okay.
Really, moving bodies, but bodies
undergoing some kind of acceleration or rotating, right?
Because whenever you're rotating, you have acceleration and stuff like that.
Statics is very easy, actually. The entire course can be pretty much summed up by "sum of forces is zero"
and "sum of moments" is zero. And that's
basically static, so now you're done.
So, write this out "sum of forces," 
and then "sum of moments."
There you go. Not spinning. And we spend a lot of time studying statics particularly.
And you may say, "Well, why? Because, I mean if nothing's going on, why is this such a
complicated issue?" Well, part of it is
that we design things in general, hoping
that they don't move. You know, like when
you design a table, you really don't want
it flying through the air, and if you
design a computer mouse, you know, it's
not going to be...Well, maybe that's a bad
example. A keyboard. A keyboard is not
going to be accelerating. So we design
things all the time with the assumption
that they're not going to accelerate.
Throughout statics, you'll have a lot of assumptions.
The main one is always - and
it always will be - asumptions...
Assume the cow is spherical. We do a lot
of overarching, perhaps, assumptions. The
biggest being a rigid body... meaning that
all the particles in an item stay the
same distance apart.
Same... distance... apart....
And this is important because it means that you're not going to have any bending,
so no deformation. So whenever you see the word
"rigid body," you should think that there's
no deformation. So there's no bending,
there's no twisting, there's no... none of
that kind of stuff.
Nothing's actually breaking. Okay? We also tend to assume...we assume sea level. We
assume everything's happening at sea
level, so it's not like, "Oh, we're on top
of the mountain so something weighs
such-and-such slightly different," or whatever.
We assume sea level and a latitude of 45 degrees.
And this can actually not be a good assumption,
depending on what you're doing.
Obviously, if you're looking at rocket trajectories, it
matters where you fire from, so...
But in general, for statics - because it's not going anywhere - it doesn't really matter where we're starting it,
or where we're building it.
So we call this a "standard location."
Okay? So we'll stick with those as our
basic initial assumptions, and then we'll go from there.
Some things that are important to know...
some review from probably a physics class,
is you've got Newton's Law.
Remember that the force between any two particles is given by the gravitational
constant times the mass of the two
particles times the distance between
them, and that G is going to be equal to
6.673 times 10 to negative 11,
your units on that are meters cubed over
kilograms squared, which is just basically
a bunch of junk that makes the whole
thing come out to newtons, because you
want you want force to be in newtons. So
if gravitational constant has all those
silly units there, then it comes
out to be newtons.
In general, since we're assuming that
we're on earth at standard sea level and
that kind of such and so and so, we usually rewrite this as the idea that weight
equals mg, and in metric g is 9.8
meters per second squared.
It also is 32.2 feet per second squared. Okay? Good? Now, in general...this is on Earth.
On... Earth.
So the idea is that if I set the radius as the radius of the Earth, and this is the mass of the Earth,
and I use this, these all equal 9.8
meters per second. So that should have
been something that you've seen before
in physics. If you're looking at statics,
hopefully you've seen physics. Otherwise,
this is just going to be a disaster.
So, that's all kinds of fun. Now, while we're
talking about weight, one of the things
that happens all the time in statics that you'll see students do is... don't convert...not "convert"...
maybe the right word is -
don't multiply. If you have something pounds by 32.2 - or 9.8 for that matter. So what
will happen sometimes is you'll have a
force, and, you know, you'll have a little
whatever...a little particle. And we'll
know that the particle has a mass of 10,
and we'll say, "Okay, well, what's the...
what's the force that this particle has?
What's the weight of the particle?" And we'll say, "Okay, well...(let's say 10. Is that better?) 10 kilograms."
And so it's force is 10 times 9.8, which is 98 Newtons. Okay? So the force, or the weight,
of a 10 kilogram particle - it's
not a really small particle, but whatever - is 98 Newtons.
Now the problem comes in is that later on, you're going to have a problem that says,
"Here we have something that is... 10 pounds."
Okay? And because you're just kind of in the mood, you're gonna end up multiplying
this times something. Or if you're really
not paying attention, you're going to
multiply it by that, which is bad, because you need to remember that in forces, 10 pounds is a force.
This is not a mass. It is a force. So that's why they say, well, you weigh differently on earth than you do on Mars.
Because you have a
different force that your body exerts.
So, if I weigh ten pounds (well, that would be terrible)...
If I weigh ten pounds on Earth, you know, I would weigh... 33.2 pounds or something like that on Mars.
If I have a mass of 10 kilograms, that's the same wherever I am in the universe. Okay?
So let's talk right quick about your unit systems and make sure you've got these straight, because you
don't want to be doing anything weird
to pounds, because it's already force.
So if we go systems of units...
Alright you've got, basically, the
metric system, or SI (System International),
and then FPS which is a customary.
Okay, I kind of have these backwards, so let's say...
a more specific terms for what we're going to do is SI, which is metric.
And we're going to do FPS, which is customary.
Okay? We've got length, we've got time,
we've got mass, we've got force.
[inaudible]
Okay?
Your metric system for length,
hopefully you got this one.
Right?
Maybe? Meters - time is seconds.
Mass in metric is... kilograms.
And force is measured in Newtons.
Now newtons are also kilogram meters per second squared.
This is called the derived unit,
which basically means that these are the ones that we stick with and this is the one that we calculate.
Now for FPS, we've got a basic unit of length with the foot, again times seconds.
Mass: do you remember?
This is the one we never see anymore...
is "slug." It is actually the one that is
a calculated unit of pound second
squared's over feets. Feet? Feet? Yeah. And then the force is in pounds. Okay?
So these are the set ones, and then the 
slug would be the calculated one. So
whenever you see that something has a
mass of kilograms, you need to multiply it
by something to get it to a force. If
something is given in pounds, you already
know the force, so don't do anything to
it. And that's kind of, I think, the whole
point of going into this. And while we're
going into this, remember that I'm
multiplying kilograms times 9.8 to get
into Newtons...
I don't know if I said that, but again I'm assuming you've had physics so that this is kind of easy-peasy.
Make sure you've got your unit prefixes. They're really important to have. So we've got 10 to the
12th - and you know a lot of these because of computers. Alrighty, and working down from
these, you should have Tera, Giga - 
terabyte, gigabyte, megabyte, kilobyte - so
if you've been doing computers since
the eighties, these are like, "My little 1.44 whatever..."
yeah, exciting. [laughs] Centi, milli, this one's fun: micro, and nano, and pico.
If you care, these are kind of...
these three are kind of in alphabetical order.
So every once in a while, in my brain I'll confuse nano and pico,
and I'll just remember they're in alphabetical order, and that helps me.
And you've got the numbers, so
capital T, capital G, capital M, little K,
little c, little m, mu (Greek), n, and p. Okay? And here's a fun story, because my
husband's also an engineer and we like
to travel and it's fun.
And we were in Greece. And in the States,
this is, I believe micron...the symbol for
a micron, which is one thousandth of an
inch. So, one micron is .001 inches.
Okay? But in Greece, this is
just - so this is US -
but in Greece, they're using actual Greek
letters, so mu just means m, right? Because
that's m in the alphabet, and so they'd
say the bridge ahead has a clearance of,
you know, 15 meters. But being engineers,
we look at that and say, "Ha ha! The bridge
has a 15 micron clearance!" and 
we'd giggle, and it was awesome because
that's what we do for funsies. So if
anything here is just desperately
confusing, then statics is just not,
not, not going to happen. So go ahead and
review this stuff, and the reason that
these, you know, prefixes and stuff are
important - so if they say, you know, "My
particle is 10 grams," you've got to
convert that to... 0.01 kilograms so then
you can multiply it times 9.8 meters per
second to get 0.0...hold on, I can do this - .98... Really? Am I having a...go two this way, two
this way...I think I did that right.
9.... 0.098 newtons. So you've got
to make sure that you're in...that
you're in the right unit system - or the
right the right prefix. Otherwise things
get...things get kind of bumpy.
But this is a good start in making sure
that you're comfortable with all this to move forward with statics in general.
