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Non-Conductor
Food Preservation
Difference Between
Energy
Diamond
Earth
First on Earth
Black Hole
Force
Fruit Acid
Steel
First Lady on Space
Fax Machine
Charles Goodyear
Speed of Sound
Digestion
Largest Flower
Human Heart
Nine Planets
Dispersal of Seeds
Celestial bodies
Mercury
Jupiter
Tooth
Human Cell
Bacteria
Body Temperature
Dreams
Pluto
Milk rise
Allotropes of carbon
Revolution of Planets
Shadows
White Dots
Finger Nails
Filament of a Bulb
Tail of a Lizard
Space Shuttle
Fruit electricity
First lady
Pyramids
Non-conventional source of energy
Weight of Earth
Stars
Motion Sickness
Dinosaurs
Electricity
Beta Thalassemia
Test Tube Baby
Planet Pluto
Elements
Sulphur
UFO
Egyptian Mummy
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What's That Squeak?
Why are Tyres Black?
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What's That Squeak?
Shalbimtoms

While writing on the blackboard I found that the chalk made a squeaky sound if I held the chalk perpendicular to the board while writing. If I held the chalk at an angle it didn't make the sound.

What's the reason?

Answers
jayesh
If held horizontally or almost horizontally, friction between the chalk and blackboard is minimal and the chalk tends to slip while it is moved on the board. This produces the squeaking sound. If the chalk is held at an angle, the friction between the chalk and the board is greater. Now the chalk doesn't slip and so you don't hear the squeaky sound.
michael Dalton
I think the squeak is due to bits of material "bumping". If you rub your fingernail along a comb slowly there is a low pitched sound. The pitch increases the faster you run your fingernail along the comb. If you make the projections on the comb smaller, there are more projections as your fingernails pass over. and the pitch increases giving a higher note. Similarly if you rub two bits of silk together there is a high pitched sound, and most of the sound is not heard as it is ultrasound and beyond our hearing range. The follow up is "why is the chalk on blackboard sound so unpleasant."
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