Police: It Is Not Safe To Fire Bullets In The Air!

By MUNGAI KIHANYA

The Sunday Nation

Nairobi,

16 January 2005

The police are quick to fire bullets in the air to disperse “unruly” crowds. Is this safe? What happens to a bullet fired in the air? How high does it go? When does it return (if ever!) and how fast does it hit the ground?

When an object is thrown upwards, it is slowed down by gravity. Eventually it stops and begins to fall back to the ground.  The amount of force accelerating it on return trip is the same as that decelerating it when going up. Thus the object strikes the ground at the same speed as it started off with. The maximum height reached depends on its initial velocity.

A stone starting at, say, 50km/h will rise to a maximum height of 10 metres above the ground. The journey to this highest point will last only 1.4 seconds. The return also takes 1.4s making a total of 2.8s flight time. Of course, the faster the initial speed, the higher the stone will go. At 100km/h, the maximum height is 39m.

How about firing a gun in the air? The initial speed depends on the type of gun, the bullet used. It varies between 1,400km/h and 3,300km/h. Theoretically, the average bullet moving at 2,500km/h should reach about 25km above the ground. The total flight time (up and down) is about two and a half minutes.

The important thing to note here is that (theoretically) the bullet lands at the same speed as that of firing. In other words, the blow of a falling bullet is equivalent to shooting at point-blank range – it is more dangerous than normal firing from a distance! In reality, however, the air slows down the bullet considerably.

All flying objects are slowed down by air resistance. The greater the velocity, higher the breaking force. So, as the bullet rises from the gun, it is retarded by two effects – gravity and air resistance. For this reason, the maximum height reached is only about 3km.

As the bullet picks up speed when falling back to the ground, the air resistance increases. Soon enough, a time comes when the breaking is equal to the pull of gravity. From that point onwards, the bullet falls at a constant velocity. This is called the terminal velocity.

The terminal velocity of a bullet varies from about 150km/h to 500km/h depending on the shape size and mass of the bullet. This is much slower than the firing velocity, but is it dangerous? Can it kill? A bullet striking at 120km/h will cut through the skin and flesh. At 250km/h, it can break a bone. Therefore, firing bullets in the air is dangerous. A falling bullet can cause serious injury.

But one question still remains: can an object be fired upwards so fast that it never comes back to the ground? Well, that is a story for another day.