Topic -1:

Some substances float on water while others sink right to the bottom.
An object float or sink when placed on the surface of the water because, An object sinks in water if its density is greater than that of water.
An object floats in water if its density is less than that of water. When the object's weight force is balanced by the upward push of the water on the object.
Density of water is weight of the water per unit volume 
Sinking substance: stone,iron,nails,....etc..
Floating substance:plastic,ball,wooden substance etc...
Some substance are floating on the water
According to their shape. For example
Iron was sinked  in the water but ironboat 
Is float on the water according to it's shape.


Topic -2:

Soluble substances: Substances that get dissolved in water are called soluble substances.
For example, common salt and sugar.

Insoluble substances: Substances which do not dissolve in water are called insoluble substances.
For example, sand, wood, stone, chalk powder, and wax.

Topic -3:

Materials are classified into three types
Solids,liquids and gases.

Solid
Solids are defined by the following characteristics:

definite shape (rigid)
definite volume
particles vibrate around fixed axes

Ex: wood,iron,plastic....etc..


Liquid
Liquids have the following characteristics:

no definite shape (takes the shape of its container)
has definite volume
particles are free to move over each other, but are still attracted to each other
Ex: water,sugar solution,mercury


Gas
Gases have the following characteristics:

no definite shape (takes the shape of its container)
no definite volume
particles move in random motion with little or no attraction to each other
highly compressible
Example:air,carbon dioxide,methene..etc..


Topic -4:

Substances can be categorized into transparent, translucent, and opaque, based on the transmission of light through them. 

Transparent: The material which allows light to pass through it is called transparent.
examples:.gacrylic sheet, glass, water, air, etc.

Opaque: The material which does not allow light to pass through it is called opaque.
e.g. wood, iron, asbestos, etc.

Translucent: The material through which light can pass partially is called translucent.
 e.g. butter paper, thin curtain, etc.

• Some marine animals(e.g. jellyfish) are nearly transparent. Transparency gives these animals protection from predators.

• Due to translucency of pale skin, the blue veins of the human body can be seen through the skin.

. Sometimes and translucent glasses are used in windows to protect privacy. The glasses are transparent from inside whereas opaque from outside.

opaque

• Smoke and fog are translucent substances. Objects appear blurred when seen through smoke or fog.

Topic - 5:

Materials can be divided into breakable or Unbreakable 
breakable is able to be broken while unbreakable is difficult to break and therefore able to withstand rough usage.
Some solids are breakable.
Examples: glass,tea cup,mirror...,wood..etc...
Glass is the most breakable substance.
Some solids are unbreabale 
Ex: iron.