Thursday, 11 September 2014

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 :d_p = \sqrt{w_p^2 + h_p^2}
                      to calculate PPI:                          PPI = \frac{d_p}{d_i}
 
 
where
  • d_p is diagonal resolution in pixels
  • w_p is width resolution in pixels
  • h_p is height resolution in pixels
  • d_i 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 w_p = 1920, h_p = 1080 and d_i = 21.5), we get 102.46 PPI;
  • for a typical 10.1 inch netbook screen with a 1024×600 resolution (in which w_p = 1024, h_p = 600 and d_i = 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