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How is Newton's 3rd Law Responsible for Recoil?
Many people are familiar with the fact that a rifle recoils when fired. The Recoil that people experience when they fire a gun is closely related to physics and is due to Newton’s third Law. This recoil is the result of action-reaction force pairs. A gunpowder explosion creates hot gases which expand outward allowing the rifle to push forward on the bullet. Consistent with Newton's third law of motion, the bullet pushes backwards upon the rifle. The force of the bullet by the gun results in an equal but opposite force on the gun by the bullet. These two forces are the ones that put the bullet and the gun in motion. The gun and the bullet form an action reaction pair.
Though the force on the rifle and the force on the bullet are equal, the acceleration of the recoiling rifle is less than the acceleration of the bullet being fired. Though the forces are equal, acceleration depends on both force and mass. The bullet has a greater acceleration due to the fact that it has a small mass. This makes sense because you have to recall that acceleration and mass are inversely proportional, the greater the mass the less the acceleration and the less the mass the greater the acceleration.
According to Newton’s third law of motion, when one object exerts a force on another object, the second object exerts on the first an equal force in the opposite direction.
The third law of motion applies to two different forces on two different objects. The action force is when one object exerts a force on another, and the equal but opposite reaction force is the force that the second object exerts on the first. For this reason, Newton’s third law of motion is commonly called the action-reaction law. Because of this, when discussing the third law of motion people often state that: for every action, there is an equal and opposite reaction.
Simply put, this statement means that for every interaction between two objects there are two forces present acting on those two objects. The size of the forces on the first object is the same as the size of the force on the second object. The direction of the force on the first object is opposite to the direction of the force on the second object. Forces always come in pairs- equal and opposite reaction pairs.
An important aspect of the third law of motion is that action and reaction forces never balance out because they act on different objects.
The recoil on a larger and more powerful gun is also going to be greater than the recoil on a smaller or weaker gun because of Newton’s Third Law of Motion. When a bullet is fired the same amount of energy is pushed back on the rifle.
A more powerful gun will have more recoil because if a bullet is fired with more energy there will be more energy pushing back on the gun. Likewise, a less powerful gun will fire the bullet with less energy and therefore have less recoil.
For Example, the heavy-duty shotgun pictured to the left will have significantly more recoil than a small handgun such as the one pictured to the right.
This force diagram clearly illustrates Newton's third Law acting on the gun and creating recoil by showing the action and reaction forces.