Question

Why does lightning usually strike tall buildings?
Answer in 60-70 words.

Answer 1

Lightning is a sudden electrostatic discharge. The Lightning prefers the things which doesn't shorten it's path.
Tall buildings, trees generally absorb the lightning before it reaches to the ground and becomes neutral. In other words, lightning is absorbed by tall buildings. The lightning can cause a severe damage to the lifes. This sudden electrostatic damages the electric circuits, hence leading to short circuit. It may cause to blast or fires and harms the man.To avoid this, lighting conductors are arranged on tall buildings. They attract the lightning and make it reach the ground safely

Answer 2

Reason:
   Static electric charge induced in tall buildings during lightning. Taller the buildings are, closer they are to the clouds/charges flowing down from sky.  Charge induction happens more in closer objects than in far away objects.  Charge induction means equal and opposite charges come out on to surface of dry objects, when a static charge comes nearby.

Detailed reason:

Lightning is caused by a sudden and quick discharge of a large amount of electric charge from the clouds (and charged particles atmosphere) onto Earth. 

     Clouds develop static electric charges over a period of time. Due to the charge a voltage develops on the clouds. When the voltage crosses the breakdown voltage of air, then air becomes a conductor.  Then a large current current flows through air.  The breakdown voltage of air is like a million Volts. 

     When a charged object comes NEAR another dry object, opposite and equal charge is induced in the dry object. So due to this, the potential difference increases, and electric discharge happens between them with a lot of sound and light.

    Thus when charges flow down through air during a lightning, opposite and equal charges are induced in very very tall objects around there.  Metals develop the charges very quickly.  Tall metallic poles are erected on top of buildings.  They are connected to the large Earth point (potential = 0) below the building.  These poles are also called lightning arresters.  For attracting lightning towards them, these poles are sharp and thin too.

     The charges in the lightning hit the nearest object as viewed from the sky. So they hit tall buildings. As the most of the charges are taken by the tall buildings (lightning arresters), very less charge is passed to open areas without tall structures.