By: Pawitra, G.7

What is Particle?A very small piece of matter.

2. Liquid

In liquids, the forces that hold the particles together are weaker than in solids

Liquids have the following properties :

They can be poured. As they fill up a container they take its shape.

They take up a definite amount of space - their volume.

They can not be squeezed into a smaller space.

4. Plasma

Is loosely described as an electrically neutral medium of positive and negative particles (i.e. the overall charge of a plasma is roughly zero). It is important to note that although they are unbound, these particles are not ‘free’.

E.g. a) Sun

b) Fire

1. Changes in solids

When a solid is heated it expands and when it cools it contracts. The expansion of materials due to heating must be taken into account whenever the materials are likely to encounter changes in temperature. The temperature changes due to the weather can also cause expansion and contraction.

2. Changes in liquids When liquids are heated they generally expand much more than solids for a given

temperature rise. They also contract to their original volume when they are cooled. Water has a strange property – as it is cooled it expands again when its temperature drops

below 4 (degrees) Celsius and continues to expand until it reaches 0 (degrees) Celsius.

When water is cooled

Almost all liquids contract when they are cooled and when they freeze they contract further to form a denser solid. Water below 4 (degrees) Celsius is less dense than water at 4 (degrees) Celsius.

In very cold winter weather this means that the water in a lake or pond freezes from the surface downwards because the coldest water is at the surface. Fish can remain alive and active in the warmer, denser water at the bottom of the pond while the surface is frozen.

3. Changes in gases Same like liquids and solids, gases expand when they are heated and contract when they

are cooled.

Example : a) Hot air balloons

b) Explosions

In a solid the particles are held firmly together but as they get hotter, they come to vibrate strongly that they begin to slide over each other. When this occurs, the solid has melted and become a liquid. The temperature at which a solid melts is called its melting point.

Boiling

Definitions

expansion : Enlargement of a material due to its increase in size (or space that the material occupies).

temperature : A measure of the hotness or coldness of a substance.

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