Thermodynamics is the study of the connection between heat (or energy) and work. To put it another way, thermodynamics is the science of putting energy into a system (whether it's a machine or a molecule) and getting it to work. Alternatively, we may be able to change a system to make it create energy (for example, by spinning turbines in a wind turbine or a power plant that generates energy). On the other hand, pressure is a measurement of the force applied per unit area on a substance's boundaries (or system). It is caused by the collisions of the substance's molecules with the system's boundaries.