Consider hammers, clubs, guns, knives, brass knuckles, blackjacks, spikes, and swords. What are the advantages of using a weapon in a fight as opposed to just using your bare hands?
Note: I have heard on this site that "Knives and all weapons are "force multipliers". "
Any weapon (well maybe except brass knuckles) will keep an opponent farther away than they would come if you had none - given you use it appropriately. This is a major advantage since it narrows their tactical options to harm you considerably. Historically, when two fighters similarly proficient with their weapons fought, the one with longer range typically won most of the times (given similar ranges and mobility, ie. not necessarily spear vs. rapier). That is because if your range is shorter, you need to accept more risk in order to get into range.
The main reason why any weapon (except brass knuckles, or perhaps a spike or spear), blunt or sharp, does more damage and is literally a 'force multiplier' is due to physics: The end of the weapon will have more leverage/speed compared to the movement of your fist.
Another physical reason for them doing more damage is a focus of force into a very small area of impact, namely a blade or a spike or a small area of the rounding of a nunchuck. Thereby, the acceleration of tissue in the impact area and the relative gradients of acceleration compared to surrounding tissue are much higher, even if it was hit with the same amount of force. This is also what allows blades and spikes to penetrate the skin and body, or blunt weapons to tear skin and break bone, all of which is actually pretty hard to nigh impossible to achieve with your bare hands.
Let's face it: The human body is not designed for high-velocity impact with any of its parts; it is relatively fragile. Thus, you can hit more recklessly and therefore harder than you would ever be able to with your bare hands, which actually break pretty easily especially if they happen to hit anything hard like a bone. Most boxers having their first serious fight break their hands because they are used to the damage being mitigated by a seriously thick glove.
With a weapon, you can keep an opponent farther away and hit harder and do pound for pound much more damage with essentially the very same move. It doesn't matter much whether you punch or thrust with a knife, it is the same kind of force generation, biomechanically speaking. The knife thrust will do a lot more damage if it connects, compared to a connecting punch though. That is why they are considered force multipliers.
How weapons work is complicated. We have different ways we can consider "how weapons work."
Humans devise tools to enhance their abilities. Weapons are just the tools humans devised for harming other animals and people. Some of them are explicitly for that purpose, such as many swords and polearms, while others have utilitarian uses as well, like camp knives or hatchets. The end goal for weapons is the same: do enough damage to a target(s) such that they cannot participate in combat or function any longer.
Weapons, especially of the non-explosive and non-chemical variety, generally rely on breaking bones, disabling muscles (by cutting or thrusting), or decreasing blood supply (bleeding) to achieve "damage." Each weapon will have varying capacities for each of these modes of damage-dealing. Understanding what a weapon is good at and relative advantages against an opponent is also very important to being an effective martial artist.
Frequently, weapons achieve these modes of damage by generating a lot of energy and focusing forces. Points and even blades act to focus forces, weight and center of mass manipulate how quickly it can accumulate kinetic energy and how much of that goes into the target (instead of, say, rotating the weapon after impact). Some other considerations exist, too, like recovering from a blow and not getting stuck in the target. In any case, weapons generally allow for more focused forces and/or quicker energy generation. This is one of the main advantages over hands and legs. Consult the Strain-Energy Equation if you want a more rigorous approach.
Of course, interrupting other life-critical systems is also an option (such as beheading, paralyzing, poisoning, etc). These are not as reliable against opponents who can resist. So I am just acknowledging that they exist, not the primary methods.
There are many, many techniques for using weapons. Enough for a lifetime of study and practice. There is also an equally large number of weapons to train and to master. There are some concepts that run through all of them, like distance, timing, and technique. In this respect, there is no one way that weapons work.
Even something like a European longsword (or "bastard" or "hand-and-a-half" sword) has multiple grips and literal books worth of techniques! Each grip and technique caters to one or several situations. There are good times to use them and bad times, and that's the "art" part of martial art.
There are several advantages:
Essentially weapons are vastly more powerful than anything a human can achieve unarmed. Even boxing gloves help with this, let alone a knife or a staff.
However beware of the laws of the country you are in. Carrying a weapon may or may not be illegal and using one may have other legal complications.
Besides all the advantages the other answers mention, there is another one, which is true especially for edge weapons: the time your attack is a threat is maximized. (not sure if it's the correct way of saying this)
I'll give an example of what I mean with that:
a punch is mostly effective if it hits at the maximum speed, when the arm is almost extended. If you hit while you are starting your movement, it is not doing much damage. Also, while you are pulling your arm back, your punch is not a threat to the opponent.
Now, if you think the same movement, but with a knife in your hand, your hand is a threat 100% of the time: your opponents close the distance? He gets cut. You hit him before the apex speed? He gets cut. If you miss, you can still cut him while pulling your arm back. The knife cuts anyway.
This makes a weapon a great advantage in a fight.
Whut. Surely you've noticed that wood and metal are harder than your fists? If not, punch a sword and assess the damage to your hand and to the weapon. Let's break it down:
Note: I am trying to present a physical idea in non-physical terms in the hope it will help grasp the concept of heavy weapons.
I recently thought about why hammers work, or why stones work as hammers. My thought was: Why can I hammer more heavily with a stone than without it, if at any moment, the hammer does not multiply my strength magically?
The answer lies in the moment. A hammer is not used in a moment, it is used after a period of acceleration. In simplified terms, while accelerating the hammer or stone, you continously charge it up with the momentary force you apply to it. A hammer (or stone) is not useful because of heaviness alone. It only becomes useful upon strike when it has a history of applied force in it.
Time and mass are essential. Upon accelerating a stone in your hand, you transform potential energy from your body into kinetic energy in the stone. Speaking non-physically, the total amount of energy in the accelerated stone is the product of time and force put into the stone.
There is a certain distance or time you can put into accelerating the stone - hammer throwers increase it by spinning, javelin throwers increase it by sprinting.
Now imagine a feather: You have may have distance, but because it is so light, you cannot apply much force to it before running out of distance or time.
That's where the stone's mass comes into play: Mass allows you to apply more force before running out of time/distance. The heavier the stone, the more energy you can transfer to it before running out of time/distance.
Of course, to be useful, the maximum mass of the stone is capped by your physical strength.
Weapons work primarily by offering a different object/surface that hits or is exposed to your opponent than your fist. If you use your fist, for example, your fist can be cut, bludgeoned, etc. The range advantage works by exposing a different thing to your opponent (if your opponent hits your sword it is not injuring you). The surface or material or other properties (hot or cold, electric, etc.) can have damaging effects, whereas your fist may not. Think about it: if a bat with spikes collides with your neck, it is more devastating than a fist colliding with your neck.
