Conduction of Heat.
Why does iron feel cold to the touch on a cold morning?
Because heat goes from the hand to the iron, thus giving the sensation of cold.
What is the passage of heat from the hand to the iron called?
It is called conduction.
When one end of a rod of iron is placed in a fire, does the whole rod become heated?
The whole rod does become heated.
How does this take place?
The heat of the fire passes from one particle to another throughout the rod.
What is this called?
It is called conduction.
What then is conduction of heat?
It is the passage of heat from one body to another which it touches, or from one particle of a body to another particle of the same body.
What bodies are good conductors of heat?
Such bodies as gold, platinum, copper, silver, iron, zinc, tin, and lead, in the order named, are the best conductors of heat.
What bodies are poor conductors of heat?
Such bodies as glass, wood, charcoal, wool, hair, and fur.
Fur is the poorest conductor of heat known.
Why does a piece of wood blazing at one end not feel hot at the other end?
Because wood is a poor conductor, and the heat goes slowly through it.
Why does a piece of iron feel cold in winter?
Because the iron is a good conductor, and carries the heat away from our hands very rapidly.
Why does fur feel warmer than iron in the winter?
Because the fur is a poor conductor, and carries the heat away from our hands very slowly.
Why does a wooden pump-handle seem less cold than one of iron?
Because wood is not so good a conductor as iron; hence, it does not carry the heat of our hands away so rapidly.
Why does carpet seem warmer than the bare floor?
Because the carpet is a poorer conductor than the wood of the floor, and does not carry away the heat of our bodies so rapidly.
Why does a stone pavement make our feet cold in winter?
Because the stone is a good conductor, and rapidly carries the heat away from our feet.
Why does heated iron feel hot to us?
Because the iron is a good conductor, and gives off its heat rapidly to our bodies.
Why does a piece of cloth, when heated, not feel hot?
Because the cloth is a poor conductor, and gives off its heat very slowly.
Why will a block of wood, when heated, remain hot longer than a heated brick?
Because wood is a poorer conductor than brick, and does not give off its heat so rapidly.
Why is a block of wood better than iron or brick, to keep our feet warm while on a journey?
Because it does not give off its heat so rapidly, and therefore remains warm longer than iron or brick.
Why should the wood or brick be wrapped in cloth?
Because the cloth, being a poor conductor, helps to keep the heat from passing off so rapidly.
Why does iron feel colder than water when both are at the same temperature?
Because iron is a better conductor than water, and carries away the heat from our hands more rapidly.
Are liquids good conductors of heat?
No; liquids are poor conductors of heat.
Is air a good conductor of heat?
No; air is a poor conductor of heat.
Are gases as good conductors as liquids?
No; gases are poorer conductors than liquids.
Why is water a better conductor than air?
Because the particles of water are closer together than the particles of air.
Why is iron a better conductor than water?
Because the particles of iron are closer together than the particles of water.
How do we know that water is a poor conductor of heat?
Because water may be made to boil at its surface without melting ice a short distance below the surface.
How do we know that air is a poor conductor of heat?
Because the air at the ceiling of a room may be made very warm without melting ice near the floor.
Why does a linen shirt feel cool?
Because linen is a good conductor, and there is but little air among its fibres.
Why is a cotton shirt warmer than one made of linen?
Because the cotton contains more air among its fibres, and air is a poor conductor of heat.
Why is a woollen shirt warmer than one made of cotton?
Because wool contains more air among its fibres, and is, therefore, a poorer conductor of heat.
Why is fur warmer than wool?
Because there is more air among the hairs of the fur, and it is, therefore, a poorer conductor of heat.
What fur is the warmest?
Fur with very fine hairs, like that of the rabbit, because it contains the most air.
Why is fur warmer when the hair is next to our bodies?
Because the fur and the air in it both help to keep the heat of our bodies from passing off rapidly.
Is the earth a good conductor of heat?
No; the earth is a poor conductor of heat.
How do we know that the earth is a poor conductor of heat?
Because the heat of summer warms the earth only a few inches below the surface.
How is it with the earth in winter?
In this latitude, the frost of winter reaches only a few inches below the surface of the earth.
In all parts of the earth, except in the Frigid Zones, the heat of the summer takes away the frost and ice of the winter, and the earth is warmed so that plants may grow.
Why is spring-water generally cool, even in summer?
Because the springs are mostly so far below the surface of the earth, that they are not warmed by the sun’s rays.
Why is snow a warm covering for the earth?
Because the air among the particles of snow prevents the heat of the earth from passing off rapidly.
Why does wrapping straw around a pump in winter, prevent the water in it from freezing?
Because the stalks of straw are hollow, and the air in the stalks makes them poor conductors of heat.
Will straw, wrapped around shrubbery, prevent it from freezing?
It will; because it keeps the heat of the shrubbery from passing off into the air.
Why are rooms warmer from having double windows?
Because the air which is confined between the double windows, being a poor conductor, keeps the warmth of the room from escaping.
Why is the space between the double walls of ice-coolers filled with charcoal?
Because charcoal is a poor conductor, and keeps the heat of the air from the ice.
Why do ice-houses have double walls, with saw-dust or straw between them?
Because the saw-dust and the straw are both poor conductors, and keep the heat of the air from the ice.
Why does ice melt more slowly when wrapped in flannel?
Because the flannel is a poor conductor, and keeps the heat of the air from the ice.
Why are woollen holders used about the stove?
Because wool is a poor conductor, and thus keeps the heat of the iron from burning the hand.