Introduction

You can notice that some substances float on the surface of water (like a piece of ice, cork and wood) while some substances sink in water (like nails, wet pieces of paper and a hard piece of plastic), this is due to the matter's density. Objectives:

• Determine the mass of some substances.
  
• Determine the volume of some solid and liquid substances.
  
• Determine the density.
  

Determination of mass and volume

The mass:

• Is the amount of matter the body contains.
  
• The mass is determined by using the sensitive balance and its unit is the gram (gm).
  

The volume:

• Is the space occupied by the body.
  
• There are several ways used to measure the volume depending on the matter's state and form, the unit used is the cubic centimeter (cm³)
  

To determine the volume of a liquid, we do the following:

• Choose the cylinder of the right graduation and capacity.
  
• Pour in it the liquid whose volume is to be determined.
  
• Write down the reading reached by the surface of the liquid, this reading indicates the volume of the liquid in the cylinder.
  
• To determine precisely the volume of liquid in the graduated cylinder, the cylinder must be positioned vertically therefore you must place it on the surface of a horizontal table.
  
• When you take the reading of the cylinder, the line of sight must touch the lowest point of the concave surface of the liquid as in the case of water or the highest point of the convex surface of the liquid as in the case of mercury.
  

To determine the volume of a solid irregular shape that sinks in water (like a piece of copper), we do the following:

• Put some water in the graduated cylinder and determine its volume.
  
• Put the solid object carefully in the cylinder and notice that the surface of water rises up in the cylinder.
  
• Write down the new reading (volume of water and the solid object together).
  
• The volume of the solid object = The volume of water and the solid object together – the volume of water.
  
• This method is suitable for the volume determination of a solid object whether this object is regular or not.
  

To determine the volume of a solid irregular shape that floats on the surface of water (like a piece of cork), we do the following:

• Put a suitable amount of water in a graduated cylinder.
  
• Tie the sinker (a piece of rock or a cube of copper) in a thin thread and drop it carefully in the cylinder to sink totally under the water surface.
  
• Write down the reading reached by the surface of water, this reading indicates the volume of the water and the sinker together.
  
• Get the sinker out of the cylinder, then attach to it the piece of cork and drop them together carefully in the cylinder so that both of them completely sink under the water surface.
  
• Write down the new reading, this reading indicates the volume of the water, the sinker and the piece of cork.
  
• The volume of the solid object (cork) = the volume of the water the sinker and the piece of cork – the volume of the water and the sinker together.
  

Determining the volume of a solid regular shape:

The volume of the cube:


The volume of the cube = The cube of its side length





Determination of density

Density:

• The density is the mass of the unit volume of matter gm/cm³.
  
• Density = Mass/Volume and the unit is gm/ cm³.
  
• The density is considered as a physical property of matter.
  
• The density of matter changes by changing the temperature due to the change of its volume while its mass remains constant.
  

To determine the density of a liquid, we do the following:

• Use the graduated cylinder to determine the liquid's volume.
  
• Determine the mass of a clean and dry beaker using the sensitive balance.
  
• Pour the liquid in the beaker and determine the mass of the beaker and liquid using the sensitive balance..
  
• Calculate The mass of the liquid = The mass of the beaker and liquid - The mass of the beaker
  
• Calculate the density of liquid = Mass / Volume gm/ cm³