How would you like to build the best slide OF ALL TIME?  Of course you would.  We're going to have to think about many different things, though.  The most important one is friction, or the force that stops something from moving when it rubs against something else.  If the slide isn't slippery enough, then our riders might slide down about as quickly as sticky maple syrup on a cold winter night.  That's not good.  If the slide's too slippery, then kids might rocket down the slide too fast and fly halfway across the playground.  That's not great either.  So let's look at friction and find out how to make our slide fast enough to have fun but safe enough that no one flies off into space.


Did you know that you need friction just to be able to stand up?  Don't believe me?  Try standing in your socks on a floor that's just been mopped, or watch a three-year-old try to ice skate for the first time.  Static friction is a force that stops two things from starting to move, while they're touching each other.  It's the strongest kind of friction.  Think about that moment when you are sitting at the top of the slide and you have to push off to get moving.  You are fighting the friction between your bottom and the slide.  The heavier things are, the harder they push together, and that makes the friction stronger.  That's why we'll want a slide made out of metal that's slippery and smooth enough so that it won't rub too much against the bottom of sliders' pants when they are getting started.  Once they start sailing down the slide . . . well, that's a different story.

This slide is easier to climb up than slide down.


Friction changes after you start moving.  You do not have to push through that first bit of friction anymore.  Now you can just sail along.  Kinetic friction is the rubbing between two things when one or both of them are moving.  There will be less rubbing if the slide is very smooth, or steep enough that gravity pulls the rider along . . . or if parts of the slide could spin!  What if the slide was made of rollers like roller skate wheels?!  Try it!  Wait, did you just yawn?  Still not as fast as you would like?  It looks like we're going to need to step this slide up.

Now that looks like a smooth ride.


So we have tried smooth metals, tilted the slide at a steep angle, and put in rollers.  But we still want to go faster.  What do we need?  Lubricants help take away friction and make things rub less.  You will find them everywhere.  Oil helps a car engine run better because it stops the parts from grinding into each other.  Okay, I put grease on the rollers.  We'll have our riders sit on this piece of cardboard so they do not get any grease on their pants. 

No really, you go first.


Want to try it out?  Sit on the cardboard.  Ready?  You start with a little static friction as we try to pull you forward.  Then . . . ZOOM! you are off like a rocket with kinetic friction, but not much.  You fly down the rollers, which are covered in lubricant.  Your hair whips in the wind and your cheeks peel back around your teeth until . . . SPLAT!  Oh, I forgot to warn you I put a pool full of Jell-O at the bottom of the slide.  Hey, I needed some way to keep the fastest slide safe.  But I think a little bit of Jell-O face is well worth a ride down the best slide ever.  Don't you agree?



References:

Ducksters.  "Physics for Kids: Friction"  Ducksters, 2009.  <http://www.ducksters.com/science/friction.php>

The Teacher's Corner.  "Friction Science Experiment"  Teacher's Corner, 2010.  <http://lesson-plans.theteacherscorner.net/science/experiments/friction.php>

eHow Mom.  "Science Projects on Lubricants"  eHow, 2008.  <http://www.ehow.com/list_6454166_science-projects-lubricants.html>

Popular Mechanics.  "World's Wildest Water Slides"  Popular Mechanics, 2009.  <http://www.popularmechanics.com/technology/engineering/gonzo/worlds-wildest-water-slides#slide-1>