It is possible for objects to share similar motions with other objects, an example would be a car and the driver, both are traveling at the same speed and direction. When scenarios like this occur, we call it a coupled system. This section will help develop the necessary tools to identify coupled systems and the resulting constraints that arise from this coupling.

In coupled system we often have to think about which objects have the same motion or some known relative motion. Those objects that do move together can be grouped into one system with multiple objects inside and the acceleration of the whole will equal that of the individual pieces. They may also be constrained together in some way. Think of all the objects that move together, the constraints on their motions, and the Newton's 3rd law force pairs in the video below.

Mechanical advantage is measure of how much effort it to do something without a device, such as lifting a mass, divided by how much it takes to do that with the aid of a device, such as lifting the mass with a pulley system. Mechanical advantage tells us how much easier a job is with a tool than without. A ramp with a wheelbarrow, a bikes gears, a pulley system, theses are all examples of simple machines used to create mechanical advantage.

This video will help orient us towards what a pulley system is. We'll have to go deeper into the analysis but is a good start.