Watching master chefs showing off their knife skills is a wonderfully brilliant thing to see. Witnessing the vegetable or protein of choice literally metamorphose before your very eyes from its whole manifestation to their new form feels like being in a magic show. You can’t help but cringe when you think about what would happen if the chef accidentally ended up slicing off his finger instead of the food.
With the bravado of showmanship providing a visual spectacle to our senses, what we do not see in the actions is what is happening at the knife’s blade level. I couldn’t help but wonder how this took place and happened and so did some experimentation and research on the matter. The complex and astounding science behind what seems like a normal, everyday chore in our kitchens just astounded me.
Essentially the knife is a machine called a wedge. The wedge is comprised of 2 other simple machines called an inclined plane that are put together. The main task of the wedge as a machine is to apply force in a specific area causing it the molecules to separate and split apart. The wedge takes the potential energy from a large area and concentrates it into a smaller area through its V-shape. When force is applied, which in the case of the knife is your hand’s energy plus gravity to assist it, that focused point allows the separation to occur.
The smaller the distance between both sides are, the more precise the separation will be. In the case of a knife, if the V shape is angled at a larger area, then it will result in less precise and accurate cuts. An example of this is the butcher’s cleaver. The cleaver’s main task is to separate hard bone and chops of meat instead of creating finer slices. Since this requires more force and less precision, the angle of the knife is less focused because it allows more surface area to come in contact with the meat and separate it.
If you’re still feeling a little lost, here’s another example for it. Take a sledgehammer for instance. A sledgehammer is a powerful device that can smash through an object as hard as rock or concrete. The larger surface area of the sledgehammer allows a bigger amount of force expended from you and from gravity to impact the object and this full force is seen when the object gets smashed into smithereens. The drawback, of course, is that the object is smashed and you can’t control the shape that it will end up in because of the larger surface area.
The other factor to consider for knives when cutting is the initial penetration or tearing stage. Tearing into the fruit, vegetable or meat you are planning to cut through makes it easier to accomplish and allows the area to be focused on. The most important reason why tearing into it is important is because this lessens the amount of force needed to go through the object. Once you have been able to enter the area you are about to tear into, the efficiency of the wedge along with the downward force of gravity enables the object to get separated easier.
Knives do this wonder through microscopic jagged edges on the blade end. For the knife to do an effective piercing of the object it is looking to cut, it is essential to generate a lot of friction on that surface in order to weaken the molecules and then the split occurs. Smoother objects will not create the necessary friction and will have a hard time piercing and penetrating the object. Have you ever been in a situation where you didn’t have a knife around and needed to cut your pork chop into smaller pieces? When you use a fork to do that, notice how much force you needed to expend to cut through it.
Understanding these 2 aspects of knife edges basically gives you the lowdown on why the material a knife is made of and maintaining its sharpness are essential for home cooks like us. Having a knife that pierces easily and has a fine point allows us to slice tomatoes, cucumbers, pork, beef, onions and just about anything in the manner needed by our recipes. Having a jagged edge versus the smooth edge of a blunt knife keeps us safer when we’re cutting as the knife only penetrates the area we want it to versus slipping and targeting something else like our fingers.