JUNIOR SCIENCEHeat

By the end of this lesson you should be able to OP22: understand that heat is a form of energy and that it can be

converted into other forms of energy OP23: investigate and describe the expansion of solids,

liquids and gases when heated, and contraction when cooled OP24: demonstrate the expansion of water on freezing OP25: measure the temperature of various solids and liquids at,

above and below room temperature; determine the melting point of ice and the boiling point of water

OP26: investigate the effect of pressure on the boiling point of water OP27: explain the difference between heat and temperature OP28: carry out experiments that involve changes of state from

solid to liquid and liquid to solid liquid to gas and gas to liquid

OP29: plot a cooling curve and explain the shape of the curve in terms of latent heat

OP22: understand that heat is a form of energy

Side-arm flask, plastic drinking cup, heat source, pointed support for cup.

Place the side arm flask containing water on the hotplate and let the water boil.

The cup is on a sharp point, e.g. a pencil or the holder of a compass needle.

Steam coming from the side arm of spins the cup into which little vanes have been cut.

Remove the source of heat. The water stops boiling, the steam stops - the cup stops spinning.

This shows heat energy being converted to kinetic energy.

Hero's engine

About 100 B.C., a Greek inventor known as Hero of Alexandria came up with a new invention that depended on the mechanical interaction of heat and water.He invented a rocket-like device called an aeolipile. It used steam for propulsion.

Hero mounted a sphere on top of a water kettle. A fire below the kettle turned the water into steam, and the gas travelled through the pipes to the sphere.Two L-shaped tubes on opposite sides of the sphere allowed the gas to escape, and in doing so gave a thrust to the sphere that caused it to rotate.This showed that heat was a form of energy.

OP23: investigate expansion and contraction solids, liquids & gases

Expansion contraction - topics for class discussion

Why are there lines of tar in footpaths and concrete walls?

How are metal rings put so tightly around barrels and wooden wheels?

Why are there gaps in railway tracks? Why are telephone wires loosely strung on the

poles? How does an automatic fire sprinkler system work? Why does a thick glass tumbler crack if boiling

water is added to it, whereas one made of thin glass does not?

Expansion contraction - topics for class discussion

Why are bottles of lemonade, etc. not filled completely to the top?

Why are we told not to throw aerosol cans into the fire?

Why is it dangerous to open the radiator cap in a car while the engine is still hot?

Why do water pipes sometimes burst in cold weather?

How does a Galileo thermometer work?

OP24: demonstrate the expansion of water on freezing

Dramatic on-screen Quicktime movie of an ice bomb, from the Journal of chemical education.

OP25 measure the temperature of various

solids and liquids at, above and below room temperature; determine the melting point of ice and the boiling point of water

OP26: investigate the effect of pressure on the boiling point of water

OP27: explain the difference between heat and temperature

OP28: show change of state from

solid to liquid and liquid to solidliquid to gas and gas to liquid

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OP29: plot cooling curve and explain the shape of the curve in terms of latent heat

The temperature of a tube of water was recorded every 30 seconds as it cooled from an initial temperature of 22°C

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The small container for the water can be made using a plastic pipette dropper. Cut off the dropping end, three-quarter fill with water and insert the temperature probe.

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Cooling curve data:

Time (s) Temp (C)30 2260 15.790 9.7

120 5.4150 2.4180 0.9210 -0.9240 -1.2270 -0.6300 -0.3330 0360 0390 0420 0450 0480 0510 0540 0570 -0.3600 0630 0660 -0.9690 -4.5720 -6750 -6.3780 -6.9810 -7.2840 -7.5870 -7.5900 -7.8

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Cooling Curve of Water

-10

-5

0

5

10

15

20

25

0 200 400 600 800 1000

Time (s)

Tem

pera

ture

(C)

As the water cools,

the temperatur

e drops Supercooling - particles

haven’t got organised to form crystals

yet

As the temperature drops, the energy of the particles in the

substance reduces. The particles start to join together. As the particles join together,

bonds are formed. When bonds are formed, heat is given out;

this heat stops the temperature falling further so while the liquid is changing to solid,

there is no further decrease in temperature. .

Eventually, all the water turns to ice, no more particles join

together, so now the temperature can continue to

drop

Completely cool !