Hydraulics vs. Pneumatics

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This week I read an article on pneumatics vs. hydraulics. Once interesting fact I learned was that both pneumatics create a mechanical advantage, which is why they are both commonly used in machines. It is important to read articles like this so we can understand many of the systems that power the machines and vehicles that we see and use in every day life.

Image credit: www.designnews.com

In STEM we've been learning about two different pressure systems, hydraulics and pneumatics. The two systems are similar in that they are both pressure systems used to utilize force. The difference is between them is that hydraulics involve liquids and pneumatics involve gases. Because of how spread out gas molecules are, gas can be compressed, or made more compact. Liquids, on the other hand, are incompressible. For example, if you filled a water bottle all the way to the top and tried to screw on the cap, some of the water would spill out, because the cap would take up a tiny bit of space previously occupied by water, and since water is incompressible and can't be forced to become compact enough to fit in the smaller space, it spills.

Image credit: hendrix2.uoregon.ed

Pressure is defined as the amount of force per unit area. Atmospheric pressure varies depending on how close or far you are from the cor of the Earth. If you are closer to the core of the Earth, then the atmospheric pressure will be greater, because the gravitational pull on the air molecules is stronger and the mass of the air molecules higher up also contribute to the pressure.

Pressure also changes based on the state of the container the substance is in. For example, the pressure in an open container containing liquid only pushes down, and as with the air molecules causing atmospheric pressure, the pressure in an open container increases deeper in the water because of the mass of the water above it. In a closed container, the water is occupying less space than it wants so, so the pressure it applies is spread evenly in all directions.

Mechanical advantage is how a tool or machine can be used to amplify the force put into it. When relating to mechanical advantage, the relationship between cylinder size and force is proportional - applying a small force to the small cylinder results in a large force applied to the large cylinder. However, the relationship between cylinder size and distance is different. The small cylinder has to move a greater distance for the large cylinder to move a smaller distance.

It is important to think about mechanical advantage when we want to create a hydraulic arm so that we can understand and utilize it to increase the efficiency of the arm, and so we can use it to move heavier objects with less force When building the arm, it is useful to use syringes of the same size and differing sizes. If you want the amount of force you put in to be equal to the output force, use two syringes that are the same size. If you want to put in a smaller force for a greater distance to get a greater output force for a shorter distance, use two syringes of differing sizes.

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