CHAPTER 4

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THE CHARACTERISTIC OF SUBSTANCE BASED ON ITS FORM

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SUBSTANCE

DEFINITIONSubstance is something occupying the room and has mass. According to the particle theory, substance consists of particle that its size is very small, related, and keep moving on. THE CHARACTERISTIC OF SUBSTANCE BASED ON ITS FORM

SUBSTANCES

SolidGasLiquid

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SUBSTANCE Solid is a substance that has a constant form and volume. Liquid is a substance that has a constant volume, but the form

changes following the place where it is. Gas is a substance that both its form and volume are

inconstant.Table : characteristic of solid, liquid, and gas

characteristic Solid Liquid Gasform

VolumeCompressibility

Specific Mass

Streaming

constant

constantuncompressed

Generally has high specific massNot streaming

Follow the place

constantHard to be

compressedMedium specific

massStreaming

Follow the place

Depending on the placeEasy to be compressed

Very low specific mass

Streaming

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THE FORM OF SUBSTANCE

Based on the form, the substances could be divided into 3 kinds, solid, liquid, and gas. Each of them has its own characteristic, either physical or the composer particles, as follows :

A. GasThe inter-particle space changes almost without any force each other.

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PHYSICS FOR JUNIOR HIGH SCHOOL VII

THE FORM OF SUBSTANCE

B. Liquid

Example : water, oil, lubricating oil, etc. Its molecules are

relatively closed if compared with gas, but not as close as solid.

The movement of its molecules are free,

The molecules are able to move, but not easy to be separated with their colony, because they are pulled each other,

The form is easy to change, but the volume is constant.

The inter-particle space is constant and somewhat distantly spaced. The force of attraction is weaker if compared with solid, and its particles are livelier and can move from one to another place

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THE FORM OF SUBSTANCE

Its molecules are very closed and tidy.

The inter-molecule force is very strong, so the molecules movement is not free.

The movement of its molecules are limited, they only vibrate and rotate.

The molecules are very hard to be separated, so that the shape is constant.

Example : wood, stone, iron, etc.

C. Solid The particles occupies the constant position and the inter-particle force of attraction is very strong. The particles movement is vibrating on its position

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ADHESION

AdhesionAdhesion is the force among the molecules that are different.Example : Ink can stick on the paper Chalk / ink can stick on the

whiteboard Cement can glue the stone

and the sand Paint can stick on the wall

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COHESION

Cohesion Cohesion is the force among the molecules that are same.Example : The force among the

molecules of wood form a wood

The force among the molecules of chalk form a bar of chalk

The force among the molecules of sugar form the grain of sugar

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MENISCUS AND CAPILLARITY

The effect of adhesive and cohesive force causes phenomenon as follows :

A. Concave and Convex Meniscus

In our daily life, we can easily find the adhesion and cohesion, for instance, when a drop of water drop on a leaf, it would form a water-ball. It is because of the cohesive force is bigger than the adhesive force.

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MENISCUS AND CAPILLARITY

B. CAPILLARITY

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The process of capillarity in our daily life : The absorption of oil

through the wicking in primus stove

The absorption of oil through the wicking in the gasoline blow-lamp

The absorption of oil to the leaf through the filter vessel

The drop of water on clothe inside the slender bucket

MENISCUS AND CAPILLARITY

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MEASUREMENT

If it is found a capillary pipe in an interconnected-container or the diameter of the pipes are significantly different, the liquid surface in the smaller pipe will be higher than in the bigger pipe, so that the law of interconnected-container will not occur.

C. THE INVALIDITY OF THE INTERCONNECTED-CONTAIINER LAW

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