Beware the Internet

Glenn Spencer, American Border Patrol – Nov. 6, 2012

Recently I had need to find the recoil of a mortar.  I Googled the term and came up with an article - How to Calculate The Recoil of a Mortar.

In it, the author says:

...3. Calculate the recoil energy of the mortar using this formula: Recoil energy equals one-half the mass of the mortar multiplied by the velocity of the mortar round squared. The mortar's mass is in kilograms, and the velocity of the round is in meters per second. The recoil energy is usually given in joules. A joule is a unit of energy equal to the work done when one newton acts through a distance of one meter. A newton is a unit of force related to acceleration. For example, A M224 mortar with a mass of 21 kg and a muzzle velocity of 124 mps has recoil energy of 161,448 joules.

I knew nothing about mortars so I continued to use the mass of 21 kg to mean the mass of the projectile fired by the mortar.  After a few embarrassing missteps, I went back and took another look at the calculations, only to learn that the author had used the entire weight of the mortar assembly to calculate the recoil, instead of the mass of the projectile – which is typically less than 2 kg.

The recoil of a 1.8 kg projectile with a muzzle velocity of 124 meters per second is 13,838 joules – or somewhat less than the 161,448 joules the author came up with.

So be careful when you use the Internet. It can lead to real trouble.

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