[deep breath]
[straining]
Oh, hello fellow scientists! It's Justin again. Welcome back! ...Um, I bet you're wondering why
I have this huge bucket of slime with me. Excellent question! See, my older sister
is super into pranks, and I've got the perfect prank just for her. All I gotta do is take this
huge bucket of slime over to my parents' house, and then up the stairs into my sister's room.
Uh... I don't know if you noticed, but, uh, I've been at this all afternoon and I just
can't MOVE this bucket. I think it's time to enlist the help of some simple machines.
By the end of today's lesson, you will be able to identify two more types of simple machines
and explain how they help us to do work. Let's get into it!
In our last lesson, we learned that simple machines are devices
that make work, or exerting force on objects to move them, easier,
either by changing the direction or the amount of force required. We also learned that
levers are very helpful simple machines that we can use to lift heavy objects. Trouble is,
I don't really need to lift my bucket. I just need to move it down the street to my parents' house.
Luckily, I think I know a simple machine that will do the trick: the wheel and axle.
You've probably heard of a wheel before. It's a round, disc-like object that can roll on its side.
By itself, though, a wheel actually doesn't do that much to help us make work easier,
but once you put an axle or a rod through the center of that wheel, then the possibilities
are endless. Axles are what allow us to carry loads on top of wheels, and they allow us to
connect several wheels together. Axles can also be what causes the wheel to turn in the first place.
Objects that use wheels and axles are everywhere: cars, trucks, scooters,
roller skates, even my little sister's tricycle, all use wheels and axles.
They are a crucial part of being able to carry heavy loads over long distances.
Wheels and axles aren't just used for transportation though. Take a windmill
for example. The wind pushes on the blades which are connected to a wheel, and that
wheel spins an axle. Now that redirected force can be used to accomplish tasks like grinding
wheat to turn into flour, or even generating electricity. Even a doorknob is an example
of a wheel and axle at work. Spinning the knob, the wheel turns an axle which releases a latch,
allowing the door to open. Can you think of any other places where wheels and axles are
used? Pause the video now to jot down your thoughts in your guided notes.
Wheels and axles are probably so common because we use them for all sorts of different things.
Sometimes we use wheels and axles to redirect force, sending it in directions that would be hard
for us to do ourselves. Like with the windmill,. When wheels and axles are used in transportation,
like in cars and scooters, they actually decrease the amount of friction between the load and the
ground. Less friction means less force required to move the object over a long distance.
That actually sounds like exactly what I need right now!
My wagon has wheels and axles at the bottom! If I put my
slime into that, that will make it much easier to get the book at home. Let's go!
Whistles
a tune]
Phew! Alright, mission accomplished.
Only... now we have to get the slime up the stairs to my sister's room. Wheels and axles are great,
but I don't think my wagon is going to help me safely get all this slime up a flight of
stairs. So maybe a different simple machine can help us out here: a pulley. A pulley is another
simple machine that also uses a wheel, only in a much different way than with a wheel and axle.
This wheel has a special groove around its edge that's designed to hold a rope or some chains.
If we want to lift an object using a pulley, we can tie a rope to it, put the rope over the wheel,
and then just pull the rope down from the other side to lift the object. Get it? Pull? Pulley! Eh?
Pulleys are great at redirecting force. Even though it will take the same amount
of force to lift this object with a pulley, pulling down on something is usually a lot
easier for people to do than lifting an object up themselves. We can even
decrease the amount of force required by adding more wheels to the pulley.
Pulleys are everywhere. If you've ever seen a big construction site, you've definitely seen a crane,
which is basically just a big pulley. Cranes are used for moving heavy materials and other machines
between the top and bottom of buildings. They're super important to construction.
And, once the structure is built, pulleys are used inside of it too. The elevators used to lift and
lower people between floors operate using a pulley system to move the elevator cars up and down.
Pulleys are great for helping us lift heavy loads, but they're also just really good at
helping us get objects to inconvenient spots that are hard for us to get to,
like the top of a flagpole or even the top of your window.
Can you think of any other places where you've seen pulleys in action?
Pause the video here to write down your observations in your guided notes.
I think a pulley is the perfect simple machine to get my slime to the top of the stairs. So we've
tied it to the bucket, we pulled down on the rope which turns the wheel, lifting the load...
And there we go! We've gotten the slime to the top of the stairs.
While I finish setting up my prank, let's review everything we've learned today.
A wheel and axle is a type of simple machine made of a disc-shaped wheel and a rod running
through the middle of it, the axle. Wheels and axles help us to do work by decreasing
the force needed to move loads or by changing the direction of the force.
A pulley is a simple machine that uses a wheel and a rope to lift heavy objects
by connecting the load to one side and pulling down on the other side.
They make work easier by changing the direction of the force or decreasing the force needed
as you add more wheels.
To find out more about wheels, axles, and pulleys, be sure to check out the activities and practice
questions for this lesson. But now, after all my planning, all my preparations, my prank is nearly
complete. My sister's gonna love this! All I gotta do is get into her closet door and...
[pop]
...And it seems like she was expecting me. Great. Ugh! I guess I got to be sneakier next time.
Once I uh... [cough] [cough] [clears throat]
...get all this glitter off me. So until then, remember:
Science is all around us. See you next time!