Wedge Friction Video Lecture - Mechanical Engineering

welcome to our lecture online now let's
talk about the wedge the wedge has some
very practical purposes in mechanical
engineering and here's a what we call a
typical example of how we deal with
wedges a wedge is an object that is used
to split something open like you put a
wedge in a log for example to split the
log or you could put a wedge in
somewhere to lift an object like we do
in this example we also use the concept
of a wedge when we talk about the screws
how you when you type in or loosen the
screw you push something up or down and
the concept there is exactly the same
we'll see some examples of that as well
so what's happening here is as we drive
using a force a wedge in between the
object a and the object C object a will
go upwards so we're trying to get an
upward motion on a by driving in this
wedge the question is how much force is
required to lift up an object like
object a well we draw some Freebody
diagrams will start with object a in
itself object a has a weight equal to mg
and that way this counterbalance of
course with the normal force on the
bottom surface we also have a friction
force here as we're driving this wedge
in here we push object a into the
surface at D there'll be a friction
between DNA and so as you're trying to
push the object a upwards there'll be a
friction force pushing downward as well
which means the upward normal force at
the bottom of a which is caused by
driving the wedge in here has to both
lift up a and counterbalance the
friction force at surface D we can also
see that the force driving the wedge in
here will cause a friction force exist
between B and a which causes a force to
act on a in the positive x-direction
that's the friction force that a which
is the normal force at a times mu that
will then cause a normal force that
exists on the back surface here called
the normal force a D which then causes
the friction force over there the
greater this fiction force the greater
the normal force here the greater
friction force there notice the friction
force at a is equal to the normal force
at D and eventually or finally you can
say that if n sub a is large enough to
overcome both the weight of object a and
the friction force Rd if n sub a is
greater than the weight and the friction
force the object will go upwards so
that's the ultimate objective here to
get a to go up to drive the wedge in
there if we look at the forces on the
wedge here notice we have n sub a also
acting downward to the top surface of
the wedge we have the force trying to
drive the wedge in and we have a normal
force at the surface B here notice the
normal force is slanted and we have an
angle here relative to the horizontal
typically those angles are fairly small
notice there will also be a friction
force at B against a wedge and so
there'll be a resultant force which is
the vector sum of these two forces the
normal force at B and the friction force
at B also notice the magnitude of the
friction force at a here is the same as
the magnitude of the friction there
because these are forces sliding over
one another eventually what we can now
do is draw a diagram here of the forces
acting on the wedge we have the normal
force acting downward we have the
resultant force at the bottom surface
which is the sum of these two forces
right here and then we have the net
force driving the wedge in the net force
will be equal to the force here that's
pushing against the wedge minus the
friction force there which is pushing
back so the net result of that is the
net force driving the wedge n notice
that the more force you apply the
greater n sub a can be with other words
as you apply a greater amount of force
you can lift up a larger object up here
also notice that of net force here
driving the wedge in is typically much
smaller than the force right here the
weight of the object and the friction
force keeping it from sliding up so
that's why this is kinda like the
mechanical advantage portion of this
problem a very small amount of force
driving a wedge in can actually lift a
very large object up and that
why wedges are used in various
circumstances notice that the friction
force in the bottom surface is already
taken into account in the resultant
force R right there and those are the
basic concept of what we called the
wedge the wedge is used to use a fairly
small amount of force to create a large
force pushing some large object in this
case a relatively small F will cause a
large weight here to be lifted up and
just by driving the wedge in there and
that's how we're going to look at the
concept of the wedge in some example
problems coming up that's how it's done