Suspension

(Norsk)
Destin, from one of my Youtube-channel favourites, Smarter Every Day, has recently uploaded a new clip which you can see at the bottom of this post. Amongst other things it show a suspension system works. One of the simplest and most commonplace examples of using a spring suspension system is a standard ballpoint pen. In my case, it is my trusty pen from NITO (the Norwegian Society of Engineers and Technologists):

When you push a spring together, you notice that that the resistance grows greater. This is because the force needed comes from this expression: F = cx. Here c is a constant for this specific spring, depending on the shape and material of the specific spring. As shown below x is the distance the end of the spring has moved compared to the initial position.

So, the more you compress the spring, the larger x becomes, and the larger the needed force also becomes. The same happens in a cylinder where you push the piston inwards. Here the force needed comes from the expression: F = pA, where p is the pressure and A is the area of the piston head. When the volume on the inside decreases, the pressure increases, and so also does the force necessary to push the piston further.

But, as Destin and the guys from NASA show in the clip below, a way to avoid that increase in resistance, is to use a cylinder with vacuum instead. The vacuum remains constant, even though the volume increases as you pull the piston outwards, and thus the resistance remains the same. Brilliant!