Physics Demonstration: Friction


Uploaded by cafedurhamcollege on 10.08.2012

Transcript:
In this physics video we are going to take a look at how gravity affects motion along
an inclined plane. And also how friction comes into play as well.
Ok. So to study motion on an incline plane, we’ve
got some equipment. Laptop, of course, to record the data.
We have our inclined plane itself. Our aluminum ramp.
And we have a motion censor. We also have, up at this end, we’ve got
our angle indicator, we’ve got a frictionless cart to test without friction first of all,
and then we have our friction containers with different surfaces.
Ok. To start with then, we going to start a simply
zero degree angle or horizontal. Now if I put something on a zero degree plane,
nothing happens of course. It doesn’t move.
And this cart represents zero friction. We have a little bit of sliding friction,
but it is very close to zero. Now to get it moving, we’re going to actually
have to incline the plane. We’re going to lift it so that the gravity
that’s pulling it down towards the earth is now redirected.
Some is down towards the earth, but some is now directed towards the end of the ramp.
So as we elevate it, it doesn’t take much, with a low friction car for it to move.
Now let’s take a look at other non-zero friction containers.
In this case, we’ve elevated the ramp a little bit, but now instead of a zero friction
car we’re going to use a box that has some friction.
Although it’s a very smooth surface and we’re going to add some weight, 250 gram
weight, (noice), and we’re going to place it on the ramp.
Now of course, the car was easily sliding by,by now, but this doesn’t yet slide.
There’s enough friction to hold it in place. So now we’re going to increase the angle
and as we increase the angle we reach a point where there is enough force acting down the
ramp (noice) that the box starts to slide. This is our first set of data.
We have the box with a smooth plastic bottom just starting to slide and it slides towards
the stop. So we see it at rest, sliding, and then the
sudden stop at the end. We see that, as it’s sliding, notice that
this has a slight curve to it, it’s not a straight line.
This box is accelerating as it slides down the ramp.
Now what can affect that? First of all we can test whether or not weight
affects it. So we add weight (noice) or mass and we place
it on the same slope that had it sliding (noice) and it continues to slide.
So weight does not provide any extra friction. (Noice)
Let’s try surface area. I now have two boxes with the same surface.
Both of them at the same weight. We’re now doubling the surface area and
surprisingly (noice) that doesn’t seem to affect it.
In this data collection we’ve got the two plastic boxes connected together so we’ve
got twice the surface area. As you can see in this one, we’ve got basically
the same type of slope slightly curved uh..oh and little bit of a glitch at the end where
it smacked into the stop. But, otherwise, we’ve got the same type
of acceleration and we see that surface area. The amount of surface area doesn’t really
affect the friction. More surface area, we still have (noice) the
same frictional force trying to hold it back. So what can affect it?
Well, we can try different materials. We’ll start off with this felt material.
Again we use the same weight (noice) 250 grams on our incline and nothing happens.
So the felt is providing a little bit more friction.
We increase the angle and we can find the angle at which it starts to slide.
So a little bit more angle and the felt starts to slide.
Trying another surface, we can try a cork surface.
With this cork (noice) surface we’ve got a lot more grip and it’s not going to slide.
So again we can try raising it and find the angle at which it will start to slide and
with this cork it’s going to be quite an angle.
We might even lose our sensor first. (Noice)
Now there we’ve got the cork sliding. So that gives us an idea of how friction is
affected and motion operates on an included plane.
So what we saw was the angle was critical for determining when the block would start
to slide. Friction does not so much matter about surface
area, but on type of material. (Music)