Explain this law of physics- correctly?

Question

in the movies you see a guy with a shotgun or other firearm. he shoots someone and knocks them 30 feet through the air from the blast but nothing happens to the shooter from the recoil. what's wrong with this and what is the physical law it defies.

i'll take 20 answers the most logical gets the ten points

Answer 1

every action makes an equal and opposite reaction

therefore, the guy who shoots the gun should also fly back 30 feet (assuming he weighs the same as the other guy).

none of this happens in real life

Answer 2

The bullet isn't hitting him..

Answer 3

This is defined by Newtons First law. Every action has an equal and opposite reaction. In other words, forces come in pairs. If someone shoots another person with a shotgun, in order to make the person go flying back, the shotgun pellets would have to generate enough kinetic energy to knock a full grown man backwards. Now, this COULD happen if the person getting shot is wearing a bullet proof vest. The reason for this is because when someone gets shot, most of the kinetic energy is lost because the bullet passes through (or almost passes through) the persons body.  If the bullet makes contact with the vest ALL the energy that the bullet gained from being fired is then transferred to the body of the person.  This however might knock the person down but no one is flying back.  Think about it logically. A bullet weighs practically nothing.  And its energy it gains is based on its mass (as well as other factors).  The bigger the mass the more kinetic energy it will gain.  

Here is another way to look at it.  I mentioned earlier that forces come in pairs. When you fire a gun, all the kinetic energy that the bullet has also acts in the opposite direction on the gun. This is the guns "kick back" THAT is the force of the bullet.  If you shot a gun and it knocked someone back, YOU would also go flying back as you shot it.

Hope that helps...:D

Answer 4

Yes, the knocking "30 feet thru the air" is an exageration if the shooter also isn't knocked back. The amount of energy needed by a bullet to do that is enormous and one should expect the shooter to be launched off his feet. Also if the bullet is allready packing that much amount of energy, it should have ripped clean through the other side. Not to mention that to create such energy you would have to pack a lot of gunpower for one measely shell, and liable to have the gun explode into shrapnel.

It defies newton's third law (for every action there is an equal and opposite reaction) and the law of conservation of energy - atleast.

Answer 5

Lex III: Actioni contrariam semper et æqualem esse reactionem: sive corporum duorum actiones in se mutuo semper esse æquales et in partes contrarias dirigi. All forces occur in pairs, and these two forces are equal in magnitude and opposite in direction.

Answer 6

In real life, the victim could be knocked off balance. but not blown away.  I like the older movies where the actors cringe with emotion and takes a few seconds to die.  According to the Staussburg incapacitation test, this is more realistic.

Newtons third law of momentum dicatates that for every action there is an equal and opposite reaction.  In the gun world we call this recoil.  For the sake of argument lets say a semiauto shotgun is being used. The slug moves forward while the gass pressure is accelerating the bolt back.  The bolt transfers the recoils smoothly through the recoil spring then shocks the shooter back when the bolt hits full back.  Then the recoil is smoothly transfered again as the recoil spring pushes the bolt forward.  Regardless if the shotgun is semi auto or just plain break barrel, the momentum is the same, the sami auto transfers the mass at a slower rate.  The slower rate has less power and therefore less "percieved" recoil.

The effects of the blast is felt by the shooter, therefore the shooter and victem will experience the same momentum transfer.  That is mass times Velocity.  The longer the shot, the more energy is being attenuated by air friction.

The victim however will experience something else. Collision with higher energy on with smaller surface area.  His body cannot absorb the energy at the surface so the shot must dissapate the energy by going trough the flesh and bone.  If unexpeccted, the victim can be knocked out of balance and then out of conscienceness.

Answer 7

Movies are typically fiction.

But you are absolutely correct.  The conservation of momentum does indeed indicate the shooter and the victim should be shoved the same amount, but in opposite directions if they are similar masses.  Here's why...

At the muzzle, Mv = mV; where M is the shooter and m is the bullet.  The shooter's velocity would be v = (m/M)V  At the vic, mV = Mu; so the vic's velocity u = (m/M)V = v.  And there you are, the vic's velocity is u and the shooter's is v.  But u = v or u - v = 0 showing they are equal but opposite velocities.

Good observation.

PS: The vic's velocity presumes the bullet is embedded and does not pass through.  And, while embedded in the vic,  I discounted the bullet's mass m <<<< M because its very small compared to M.

PPS: A shooter braces herself when shooting; so she is not knocked backward by the recoil (the energy from the v in the equations above).  Also, some weapons have recoil absorbing spring-like mechanisms to help absorb the recoil.

Answer 8

the law of physics states that in every action, there is an equal and opposite reaction. In your case, the barrel of the gun for whatever gun it is, absorbs the force or the action. It might only be a tendency of over-acting as the actor was told by the director.

Answer 9

No physical law is defied if the shooter is leaning on a wall. Therefore the person who shoots will not be thrown away. But there is still an equal amount of forces exerted.

Also there will be no physical law to be defied if the shooter is much much more heavier, that the force to be exerted on him will be resisted; the person to be shot must be too light that he is blown that far.

Answer 10

The law involved in this question is Newton's Third Law of Motion, which states that for every action there is an equal and opposite reaction. The bullet being shot out of the gun barrel is the action, so there should be a reaction, acting in the opposite direction - this happens to be the recoil, which pushes the shooter backwards, or jerks their arm upwards at the elbow.

There's no way a person could shoot a firearm and not be pushed backwards. Even if they were supported from behind by a wall or something, the reaction force would be transferred into that...in fact, if a person fired a shotgun whilst standing in front of a wall made of weak polystyrene, they would probably be pushed backwards and through the wall, which would break under the force of the reaction.

When a person is shot, they also may be thrown backwards. This is due to the Law of Conservation of Momentum, whereby the bullet slows down but transfers momentum to the body.

Hope this helps ;)

Answer 11

Well, if we had a gun that would also kill he shooter our murder rate would drastically decrease. If you had been in the military, you would know that you get a kickback when you fire a gun or a rifle.

The reason you feel the kickback is that the powder that is ignited puts an equal pressure against the bullet and the back of the barrel.

If you did not anticipate the kickback you can be knocked on your a**.

Experienced shouters brace themselves, by perhaps placing one leg a distance behind the front leg. So, the principle (Newton's) for every force there is an equal reactive force is valid.

Once the bullet flies through the air, there is no longer any force on it, because Force = ma, and there is no longer an acceleration. The maximum velocity the bullet reaches, is reaches at the moment it leaves the barrel. The bullet now has momentum and kinetic energy.

Obviously, the bullet once leaving the barrel exerts no longer a force on the shouter. As the bullet hits its target, the target has to absorb the kinetic energy and momentum of the bullet. Damage to the victim absorbs most of the energy if the target were a human being, if it were a concrete wall, the energy would turn mostly into internal energy, the bullet would be smashed and its temperature would rise, if the target would be a light object that would not break, it would fly off while it would assume some of the momentum of the bullet.

  

Answer 12

To be breif, bnot every gun has a recoil, theres a lot of physics which most of you in your over complicated ways have ignored, but lets not go there...

Answer 13

the shooter must recoil in opposite direction by same amount of force he exerted...

but to in the movie.. they need to make the hero to look macho n stuff.... so they defies the law of physics....