How Knife Throwing Works

Knives have been around longer than modern humans have. They were among the first tools our hominid ancestors produced, and we have since developed them into specialized versions suited to an endless variety of tasks, from hacking through jungle to performing eye surgery. At times, knives have represented freedom and independence, the ability to survive [source: Ewalt]. But they've never lost their sense of danger.

One of the more interesting examples of this violent versatility is the wide variety of throwing knives found among African cultures. From the Sudan down to the Gabon and the Congo Basin, blades for throwing assume a variety of surprising shapes and sizes. Some measure as much as 2.5 feet (0.76 meters) across; many are curved, or sport long handles; some look like police batons, while others resemble large, drunken throwing stars, sickles or the heads of polearms. They feature multiple nasty edges designed to ruin the legs of men and horses, and warriors throw them using a wrist-snapping sidearm that spins them in a lateral arc toward their targets [source: McNaughton].

No one can say when people first started throwing knives. Likely, it was sometime after blades assumed a more balanced, single-edged form around 5,000 years ago [source: Ewalt]. We like to imagine the activity began, as so many do, from boredom. Probably, tossing a knife at the ground or a nearby tree stump took the edge off fireside boredom or provided a way to cull the rodent population. From there, it may have advanced via a series of competitions or challenges into a way for warriors or hunters to display their skills.

This is mostly speculation, but we like to think that the decision to cross over into William Tell territory was likely based on a dare (we refer doubting readers to YouTube and the Darwin Awards). Whatever its origins, the impalement act has entertained crowds at circuses and Wild West shows since at least the late 1800s. The danger and skill on display in such acts, especially those involving a blindfolded thrower or a comely assistant strapped to the spinning "wheel of death," have caused many to suspect fakery is afoot [source: Hart]. But in truth, although stagecraft tricks exist for simulating knife throws, most impalement acts are perilously real [source: Esquire].

So how do they manage to never hit their assistants? Well, as world-record knife thrower David Adamovich told Big Think, "They last a lot longer if you throw around them than if you throw at them." Even so, throws do sometimes go astray [sources: Adamovich; Esquire]. Humans, after all, are fallible, and physics is unforgiving.

Whether you throw by handle or blade, whether your preferred missile is a knife, ax, tomahawk or some other pointy object, the basic rule of throwing is the same: Grip the light end and throw heavy-end first. Just as when a juggler spins a set of clubs skyward, this arrangement creates a natural motion that encourages spin and stability [source: Janich].

As you swing your arm toward the release point, you impart two kinds of motion to the knife: First, you move it in a partial circle around your shoulder joint; second, you create spin. How? Because velocity = distance / time. By the time you've completed your swing, the outer end of the knife has moved a greater distance than the end that you are gripping, but in the same amount of time. This differential motion imparts spin, which is influenced by center of mass, which is why knife balance is so crucial.

What path does the knife take? Well, physics tells us that a revolving object that suddenly breaks free will continue to move in a straight line tangential to the point at which it was released. For this reason, the release point for a knife throw occurs much earlier than most people expect -- at the top of the arc, not at your arm full extension [source: Thiel]. If you let go at the end of your throw, the knife would instead fly into the ground.

Of course, this is an idealized case, and the actual arc, motion and release point will depend on your throwing style.

Once released, the knife flies toward the target at a speed averaging between 26 and 30 mph (42 to 48 kph) [source: Adamovich]. If you've brought all the throwing elements together properly, then the knife completes its rotation just as the business end points perpendicular to the target.

Now the weight of the knife comes into play. Since momentum is proportional to velocity and mass, a knife with some properly proportioned heft considerably improves your odds of sticking in the target. A sharp point is essential, too, because pressure, which drives the knife into the wood, is inversely proportional to the area of contact. If you've ever had a cat wake you in the morning by putting all of its weight on one kidney-punching paw, then you are familiar with this concept. This is a good thing, because it's going to help you choose your weapon.

Like anyone who has tried to put together Ikea furniture without a hex wrench, knife throwers know that success, especially for beginners, depends on choosing the right tool. So before we get into how to throw, let's spend a moment to consider the qualities that make for a good throwing knife.

As hinted at in our physics section, a good throwing knife relies on the right combination of three factors, in the following order: balance, weight and length [source: McEvoy].

There's a bit of a chicken-and-egg relationship between knife balance and the kind of throwing you plan to do. As we mentioned in the previous section, you'll want to throw heavy-end-first, and your knife will reflect that. If balanced for handle-throwing, then a knife's center of mass is shifted toward the tip; if balanced for blade-throwing, the opposite will hold true. Some knives are balanced to be thrown either way, with the weight balanced dead-center [sources: Branton; McEvoy].

We've already seen that weight determines whether your pig-sticker packs enough punch to pierce the target, and that this heft must be balanced for throwing. A good rule of thumb is to select a blade that weighs roughly 1 ounce per inch (11 grams per centimeter) of total length (not blade length) [sources: Branton; McEvoy]. Most throwers use knives weighing more than 10 but less than 16 ounces (283 to 454 grams). If you do the math, that means a typical knife length runs from 10 to 15 inches (25 to 38 centimeters). Note that a longer knife means a slower rotation, so some experts suggest a knife of 12 to 14 inches (31 to 36 centimeters) for beginners [sources: Adamovich; AKTA; Branton; McEvoy].

It should go without saying that throwing knives should not have particularly sharp edges, especially if you plan to throw them by the blade [sources: Branton; McEvoy]. Although you will keep your fingers curled away from the blade when throwing, having a sharp edge adds nothing to the throw except the danger of cutting yourself. Remember: When it comes to sticking, it's the knife's point that matters.

As for cost, throwing knives can start in the low teens and ramp up to more than $100 apiece for custom models. Most experts advise buying the best you can afford. Cheap or poorly balanced knives can break or not perform well, leaving you frustrated and throwing off your technique [source: AKTA]. Throwing knives are often sold in sets of three or five, a worthwhile investment that can save you the fatigue and loss of focus of walking back and forth. This is important, because learning to throw a knife is all about practice, posture and finding your perfect distance.

Before you start, remember that knife throwing might feel awkward at first, but at one time so did playing a musical instrument, riding a bike or throwing a football. Any new activity requires time for your body to develop muscle memory and to gain strength. Be patient, and quit when you feel yourself getting tired or sense that your concentration is slipping.

The two most widely used throws are based on a half spin and a full spin of the knife, depending on whether you use a blade grip or handle grip, respectively. As you might imagine, a knife gripped by the blade must complete half a spin before it points in the right direction, whereas a handle-gripped knife begins its flight pointed the right way and must make a full spin to return to it. Although the total number of spins depends on throwing distance, these two styles will always involve some multiple of half or full spins.

Whether throwing by blade or by handle, the technique is the same. First, stand at the appropriate distance (more on that in a minute). Now, balance yourself by standing with the leg opposite your throwing arm forward. Present the knife to the target, sight with it and smoothly bring it back behind your shoulder. Keeping your eye on the target, swing the knife in an arcing, vertical overhand motion and release it near the top of the arc or just after (it will take practice to develop the feel of this). The knife should slip easily out of your hand. Do not whip your wrist. Follow through until your arm extends in front of you as if you were shaking someone's hand. It's common to transfer your weight from the back foot to the front during the throw.

Beyond these basics, you'll need to make adjustments based on distance, type of knife, stance, body proportions and throwing style. For a half-turn throw (blade grip), you'll usually throw from around 7 to 8 feet (2.1 to 2.4 meters). A full-spin throw (handle grip) will require 12 to 15 feet (3.7 to 4.6 meters) to complete one turn, and 18 to 19 feet (5.5 to 5.8 meters) for the more difficult two-spin throw [sources: AKTA; McEvoy].

As with most aspects of knife throwing, distance requires some dialing in. If your knife enters the target with the handle slanting toward the ground, then you are standing a bit too close. Try moving another 6 inches (15 centimeters) back from the target. If the handle is angled upward, then you are standing too far away [sources: AKTA; AKTA]. Once you have your distance, the rest is a question of grip and technique.

Just like any other throw, an effective knife throw requires developing an effective grip and a sense of what your wrist, shoulder and elbow ought to be doing throughout the motion.

For a handle throw, grip the knife like a hatchet, with your fingers curled around and your thumb pressed near the crosspiece. Some prefer to place the thumb along the top of handle, which slows rotation and lets you finesse throwing distance [sources: AKTA; McEvoy].

For a blade throw, hold the blade edge-down, with the sharp part away from your palm. Now line up your first through third fingers on the side opposite your thumb and curl your pinkie out of the way. You should have about an inch of blade sticking out past your fingers toward your wrist [source: McEvoy]. Note that, aside from finger curling, your grip, throw and release remains the same as during the handle throw [source: Janich]. This means that you don't have to learn two completely different sets of biomechanics for the two throw types.

No-spin techniques also exist, although they are less common in competition. The advantage of such techniques is that, because they do not involve spin, distance is less of a factor. However, some knife throwers argue that these methods are more tiring and harder on the joints [source: Thiel]. Your mileage may vary.

There are three main approaches to no-spin throwing. All three use the so-called "finger of God" grip, in which the thrower lays an index finger along the knife's spine to helps eliminate rotation [source: Thiel].

One technique, sometimes called mumyouan style, derives from the martial arts of the bo-shuriken, a Japanese throwing spike. It involves locking your wrist and releasing the knife with something like a push or shot-put motion. Another, Thorn Style, resembles a spear-throwing action, with arm and elbow swung well away from the body and a lot of wrist action on the release. It works best with large weapons like swords. Finally, Russian style throwing consists of a more compact motion, with the elbow held in near the body. After cocking the knife behind the ear, a Russian thrower makes a low, whip-crack motion while coming around and releasing the knife [source: Thiel].

Whatever style you choose, remember: Aim small, miss small. Try to hit as small a target as you can, then see where the knife goes and make small corrections. Adjust one element at a time, whether it's distance, grip or release point, but always try to keep the force of your throw constant to limit your variables. With a bit of practice, you'll be impressing your friends and frightening your neighbors in no time.