What is an example of rectilinear translation?

Rectilinear translation refers to the movement of an object along a straight line. In the context of the options provided, the piston of an engine exemplifies this type of motion perfectly. When the piston moves within the cylinder of an engine, it does so in a straight path, translating linearly from the top dead center to the bottom dead center during the power stroke. This is a prime example of translational movement as it follows a linear trajectory due to the force applied by combustion.

The other options involve forms of movement that do not solely adhere to rectilinear translation. Locomotive wheels, for instance, rotate around an axle, which does not constitute linear translation. Rack gears engage with a pinion and convert rotary motion to linear motion, but the gear itself does not move in a straight line. A jack may lift objects vertically, but its mechanism also involves rotational or angular movements to function effectively. Therefore, the piston provides the clearest illustration of rectilinear translation.