Now let's look at the
equation for static friction.
So static friction
is a case where
you've got two solid
surfaces in contact,
and you're trying to move
between those two surfaces.
So you're trying to move one
surface across the other.
But the objects don't slide
relative to each other.
So you're attempting
motion, but you're not
succeeding at moving things.
In other words,
the static friction
makes them stick together.
Well, the equation that
represents that is given here.
Now over here on
the left-hand side,
we have our frictional force.
Now the way our
textbook uses this,
it's a lower case f with
a subscript of an s.
Books do have an uppercase F,
but we're using a lower case f.
Over here on the
other side, we've
got the normal force, so that
F sub N is your normal force.
This is our coefficient
of static friction,
and that's the Greek symbol mu.
And because it's
static friction,
it has the subscript of an s.
We've got another
video for talking more
about that coefficient.
The last thing I want to
point out about this equation
is that the symbol
in the middle here
is not an equal sign, but
a less than or equal sign.
So we want to explain that.
We're not used to having
inequalities in our equations
here.
So less than or equal.
The force of static
friction is only
going to be as much force
is needed to hold it still.
And that means if you're
attempting to push it,
but you're only
pushing a little bit,
it only needs a little bit
of friction to hold it still,
If you push a little harder than
the friction has to increase
to keep it from moving.
Well, there's a maximum.
And that maximum is when it
actually equals mu sub s FN.
So up here you're going to
have less than mu sub s FN.
But here there is a maximum
amount that you can push.
If you push too hard, more
than that maximum amount
than friction can't
hold it still,
and you do not have
static friction
anymore because static
friction has to hold it still.
So there's a maximum
amount that we can have,
but anything else you're going
to have less than that maximum.
So this is our introduction
to static friction.
You're still going to need
to see some work examples
before you really get this.
