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Name: Willie C.
Status: other
Age: 40s
Location: N/A
Country: N/A
Date: Sunday, September 15, 2002

If the wonders in space were created by a big bang, what happened to the recoil?

Willie -

Good question with a cool answer... If the big bang did really happen, the explosion sent matter of all sizes in all directions... but if you were to measure the momentum of all the shrapnel it would add up to zero. Momentum is the key to your question.

To understand this, it is important to realize that momentum is the product of mass and velocity and - important - velocity is a vector quantity. It has direction. So therefore... momentum is a vector quantity. And, when you add up the momentum values in varying directions, the total is zero.

Any momentum found in an object in the universe is only situational. If we knew all the momentum quantities - the momentum of every object in the universe (including the baseball thrown by a pitcher), we would find that the sum of all is zero. An interesting concept and one that (to me) makes a great deal of sense.

A lot of the challenge in life is asking good questions. You asked a good question.

Larry Krengel


The recoil was part of the big bang. If an explosion pushes something in one direction, it must push something in the opposite direction as well. This is the recoil. The big bang pushed in all directions at once. Part of the explosion went "up" and part went "down". You could call the "up" part the push and the "down" part recoil, or the other way around. The same holds with "left" and "right". When gunpowder goes off, it pushes the bullet one way and the rifle the other. Because the rifle is heavier, it is not affected nearly as much as the bullet. We say the push on the gun is the recoil because the gun moves less. We could just as correctly say the push on the bullet is the recoil of pushing the gun.

When a rocket fires its engines, the rocket gets pushed forward and the burnt fuel gets pushed backward. In a "recoilless rifle", the bullet gets pushed forward and a great deal of expanding gas gets pushed backward. Every forward push has a corresponding backward push that is just as hard.

If you want to do more "research" regarding this, two official terms to look at are "Conservation of Momentum" and "Newton's Third Law".

Dr. Ken Mellendorf
Physics Instructor
Illinois Central College

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