Hello, fellow scientists.
It's Justin again and – woah, woah, woah! Phew!
Be careful, it's uh, it's pretty slippery right there.
This ice is, um... Hey! Have you ever wondered why it's so much easier to slide around on
ice than it is to slide around on other surfaces?
Well, to answer that question, we're going to need to explore the force of friction.
By the end of today's lesson, you will be able to describe friction as the force that
opposes motion and identify materials with high and low friction.
Let's get into it.
In our last lesson, we learned that a force is any kind of push or pull on an object,
and we learned that forces determine how objects move.
One of the key forces involved in motion is friction.
Friction is a force that occurs whenever two objects rub against each other.
The force of friction opposes or resists motion.
Think about it like this: Imagine a ball rolling along a flat, grassy field.
No matter how fast that ball is going, you know that it will eventually slow down and
stop.
But Newton's first law states that any object in motion will remain in motion unless acted
upon by an outside force.
In this case, that force is the force of friction between the ball and the ground.
That's what's slowing the ball down and will eventually cause it to stop.
You could try creating some friction right now.
Rub both of your hands together as fast as you can, like this.
Pretty soon, you'll notice that your hands start heating up, right?
Well, that heat is generated by friction.
Friction occurs when objects rub together because, when they rub together, all the little
bumps and uneven areas on their surfaces catch on each other, and that makes it more difficult
for the objects to just slide right past each other.
Because of this, objects with rougher surfaces
will generate more friction – things like sandpaper
and concrete – and objects with smoother surfaces will generate less friction – like that ice
I was sliding around earlier.
Now that we know that, which do you think creates more friction, wood or glass?
The wood's surface is rougher, so it would create more friction when you rub against
it.
What about a grassy hill versus a snowy hill?
The snowy hill is smoother, so the grassy hill would create a larger amount of friction.
What things around you could create different levels of friction?
Pause the video here to write down what you can see that would
create a high amount of friction or a low
amount of friction.
Remember, things with surfaces that are coarser will create more friction, and things with
surfaces that are smoother will create less friction.
So, friction is a force that opposes motion that occurs when two objects rub against each
other.
Now, opposing motion might seem like a bad thing, but there are plenty of times where
we want lots of friction just to go about our everyday lives.
Like, take cars, for example. You might think that driving a car is one of those times where
you don't want anything slowing you down, but the truth is without friction, we would
not be able to control a car's movement at all.
In fact, cars' tires have lots of little grooves in them called "treads" that are designed to
increase the amount of friction between it and the road.
Plus, friction is an important component of
brake systems that, you know, stop a car from moving
when you need to.
Also, when there isn't enough friction between the car and the road, like when it's really
icy out, we might put sand or salt or other coarse substances on the road, or even put
chains on our car's tires, just to increase the amount of friction.
Cars aren't the only places where we want a lot of friction.
Friction is responsible for us being able to safely walk down a hallway, us being able
to write things on paper, and even us being able to turn doorknobs.
To prove how important friction is, pause the video right here and go and find the nearest
shoe you can and see what's on the bottom of it.
Jot down what you see in your guided notes.
Of course, there are times where we want to decrease the amount of friction as much as
possible, like with slides on a playground.
Those things are so much more fun if you go down smoothly.
You move so much faster.
Uh, don't even get me started on slip and slides.
When we want things to be able to move smoothly for them to work well, we want to decrease
the amount of friction – like in the metal that rubs together on door hinges or with
the gears inside a clock.
When we want to decrease friction for things to move smoothly, we might even add smooth,
slippery oil as a barrier between the objects that are rubbing together.
You might have seen this strategy for yourself if you've ever gotten your hands all greasy
from touching some bike chains.
So, when I slipped on the ice earlier, that must have been because there wasn't that much
friction.
But... Do you think that I could find a way to further decrease the amount of friction between
my feet and the ice?
Yeah, I could throw on some ice skates with some smooth, sleek blades to really let me
slide around.
And, if I wanted to increase the friction to make it harder for me to slip, well, I could just
put some metal spikes on the bottom of my shoes like mountain climbers do, to really
pump up the friction.
But I gotta say, I think the low friction option sounds a lot more fun here.
Before I strap on my skates, let's review everything we've learned about friction today.
Friction is a force that opposes motion when objects rub together.
Objects with smooth surfaces have less friction, and objects with rough surfaces have more
friction.
We can increase the friction in the objects around us when we need more control,
and we can decrease it when we need things to move more smoothly.
To learn more about the force of friction, be sure to check out the practice questions
and activities for this lesson.
Now, if you'll excuse me, I think I'm going to go observe the effects of a low force of
friction for myself.
Until next time, remember: Science is all around us!
See ya!
Weeeeee!