ROCKY's
Science Fun
WHAT CAUSES 
A SQUEAK?

Science Standards by State

 
You will need
  • chalkboard
  • several pieces of chalk

 
 
 
 

  See a picture
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

 

Have you heard a door hinge squeak?  Or a shoe squeak when someone walks by?  Or a board in a wooden floor squeak when walked on?  Some squeaks are annoying, and you want to get rid of them or prevent them.  Others are only slightly annoying.  But squeaks are fun to learn about, and to cause or prevent.  Want to know how?

Get a piece of hard chalk at least as long as your little finger and go to a chalkboard.  But since a squeak may be very annoying to others, make sure you are alone in the room, or that several of you are studying squeaks at the same time.  Hold the chalk tightly between thumb and forefinger of one hand and drag the tip of it across the board.  Does it make a squeak?  Is its track on the board continuous or dotted?  So long as you drag the chalk, can you make it squeak?  Does it make a difference whether you hold it at a low angle or a nearly right angle to the board so long as you drag the chalk, not push it?
 

Now change the angle of the chalk to the board so you push it instead of drag it.  Try to:

  • hold it tightly between your thumb and forefinger while you push it
  • vary the angle of the chalk against the board.  At what angle does the chalk seem to "stutter" or squeak the most?
  • push the chalk, then drag the chalk.  Which makes it stutter or squeak?  How would you hold the chalk to make the most widely-spaced dots on the board. 
How would you hold the chalk to make the most widely-spaced dots on the board?  How would you hold the chalk to make the most closely-spaced dots?  What kind of sound is made when the dots are most closely spaced?  If the sound made by pushing tightly-held, short chalk across the board makes a horribly annoying screech, is the track still made of dots, or is it a continuous line?  How can you tell?

Wipe part of the board with a wet cloth.  Now can you make the chalk squeak on the wet part of the board?  When the chalk stutters on the board, it makes a special track that is interrupted.  The chalk sticks, then slips and takes a tiny jump to a new place where it sticks, then slips and jumps to another new place.  It is this interruption of sticking, then slipping and jumping to a new spot - over and over again, very fast - that makes a squeak.  You can see and hear where the chalk sticks on the board, then jumps.  It makes a little dot there.  But you can't hear where it jumps to the next spot and sticks.  You only hear when it sticks.  So a squeak really is a series of stick-and-jump-and-stick-and-jump ... all happening so fast that it makes a squeak.

Try making a squeak with chalk on a board that you wiped with a wet cloth.  The chalk just won't stick, and so you cannot get a squeak.  That is what happens when you put a drop of oil on a squeaky hinge.  If you prevent the sticking that is part of any squeak, you prevent the squeak.  Water could prevent a squeak, but water dries.  Oil doesn't dry quickly, so it prevents a squeak for a much longer time.

When you hear any squeak, you know that something is “stuttering” across a surface in tiny jumps.  If the jumps are very close together, they produce a shrill sound.  But if they are farther apart, the sound is of lower pitch, like a door “groaning.”  If chalk on a board cannot stick and slip, it cannot squeak.  It must stop and go in tiny jerks for it to squeak.  Putting a drop of oil on a hinge is like wetting the board.  The chalk cannot stick on a wet board.  One part of a hinge cannot stick on another if a drop of oil lets two adjacent parts only slide.

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