Four-bar linkage

Imagine you have 4 sticks, one smaller than the other three. You hold the smallest stick at one end with one hand, and you take the other end of it and attach it to the end of the second smallest stick. Then, you attach the other end of that stick to the end of the third smallest stick. Finally, you attach the other end of that stick to the end of the biggest stick. Now you have four sticks connected together, with the smallest one being connected to the next biggest one, which is connected to the third biggest one, which is connected to the biggest one.

This is what we call a four-bar linkage, and it's an important concept in engineering. The linkage is a set of four rigid bars that are connected by four pivots or hinges, which allow them to move relative to each other. When the bars move, they can create different kinds of motion or output, such as rotation or linear motion.

Four-bar linkages can be found in all kinds of machines and devices, from car suspensions to robotic arms to simple toys. They help us to transfer energy and forces from one place to another, or to change the direction of motion or force.

Overall, a four-bar linkage is a way of connecting four sticks together to create different kinds of motion or output. It's a simple but powerful concept that engineers and designers use to build all kinds of things.