What is hydraulics? Hey Engineering Lovers, what is the connection between a water gun and this giant crane? At first glance, no connection.
But think about the science behind them and you'll come to the surprising conclusion that water guns and cranes use the power to move liquids in a very similar way. This technology is called hydraulics and is used to power everything from car brakes and garbage trucks to motor boat steering and garage jacks. But let's start with some properties of matter.
Gases are easy to compress and everyone knows how easy it is to compress a balloon. Solids are exactly the opposite. If you've ever tried to squeeze a block of metal or a piece of wood with nothing but your fingers, you know it's practically impossible.
But what about liquids? Where do they fit in? You probably know that liquids are an intermediate state, a little like solids in some ways and a little like gases in others.
Now, since liquids flow easily from one place to another, you might think that they would behave like gases when you try to squeeze. In fact, liquids are virtually incompressible, much like solids. This is the reason why a belly dive hurts if you mess up your dive into a pool.
When your body hits the pool, it's because the water can't squeeze down like a mattress or diving board would, or get out of the way fast enough. This is also why jumping from bridges into rivers can be very dangerous. Unless you dive properly, jumping off a bridge into water is almost like jumping on concrete.
But the fact that liquids don't compress easily is incredibly useful too. If you've ever fired a water gun, you've used this idea. You've probably noticed that it takes some effort to press the trigger on a water gun.
When you press the trigger, you're having to work hard to force water out through a narrow nozzle. You're actually applying pressure to the water, which is why it squirts out at a much greater speed than you move the trigger. If water wasn't incompressible, water guns wouldn't work properly.
If water guns can change pressure and speed, that means in strict scientific terms that they function as tools and machines. In fact, the same science as water guns powers some of the largest machines in the world such as cranes, dump trucks and even excavators. Hydraulics is based on a simplified form in this way.
Let's imagine a pipe containing a liquid, where at one end we have a smaller diameter and another end with a larger diameter. When we apply a large force to the tip with a larger diameter at a low speed, as the liquid cannot compress, it pushes the same liquid through the pipe, causing the tip with a smaller diameter to come out with less force, but with a higher speed. This is exactly how a hydraulic jack works.
The science behind hydraulics is called Pascal's principle. Essentially, because the liquid in the tube is incompressible, the pressure must remain constant the entire way, even when you push it hard at one end or the other. Now, pressure is defined as the force acting per unit area.
So if we press down with a small force on a small area at the narrow end of the tube on the left, there must be a large force acting upward on the larger area piston on the right to keep the pressure equal. This is how the force “amplifies”. And where can we see practical applications of hydraulics?
You can see hydraulics in action on an excavator for example. When the driver wants to contract the arms, he pulls a lever and the excavator's engine pumps fluid into the piping lines and hydraulic cylinders attached to the arms, forcing those cylinders to extend. If you put together multiple cylinders and multiple positions, you can make an excavator arm extend and move like a person's, only with much more force.
The hydraulic cylinders are effectively the muscles of the excavator and they utilize the base of hydraulics to move large parts or dig the ground around. But you might wonder how this cylinder can move in and out if the hydraulic fluid is always pushing it in one direction. And the answer is that the fluid doesn't always push in the same way and direction.
Each cylinder is fed from opposite sides by two separate tubes. Depending on which way the fluid moves, the cylinder moves the piston in or out, very slowly and smoothly, as we can see in this animation. When we want to extend the arm, the fluid is pumped in the first line in one direction and relieved in the other line, and when we want to contract, the fluid is pumped into the second line and relieved into the first, and that's how the movement in the cylinders happens.
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