Physics

Density

Density is the mass per unit volume.Density tells you how much mass has been packed into a given volume of space.

The equation for density is :

At A-level we use the symbol 'ro' for density ( ) making the equation:    

                                                                                        

Densities of solids, liquids and gases

When most substances change from a solid state to a liquid state their volume does not change much. This is because the particles stay approximately the same distance apart. This means that the density of a substance, say iron, does not change by much when it melts

Density Cartoon Video

                                                        

 

Density in Computers

In computers density is involved with the pixels, the pixels affect the resolution and the visual quality of the monitor.

The equation to calculate diagonal pixel density is :

                      to calculate PPI:                          

 

 

where

• is diagonal resolution in pixels
• is width resolution in pixels
• is height resolution in pixels
• is diagonal size in inches (this is the number advertised as the size of the display).

For example :

• for a 21.5 inch (54.61 cm) screen with a 1920×1080 resolution (in which = 1920, = 1080 and = 21.5), we get 102.46 PPI;
• for a typical 10.1 inch netbook screen with a 1024×600 resolution (in which = 1024, = 600 and = 10.1), we get 117.5 PPI.
• for 27 inch screen with a 2560x1440 resolution we get = sqrt(2560^2+1440^2)/27 = 109 PPI