Mechanism

Converting Rotational motion to Linear Motion
(after looking at the videos, I'm pretty sure the Boston Museum of Science has a whole wall of these mechanisms...)

Slotted Connecting Rod
These are what are on elliptical machines. The rod moves in and out and linear-ish and while the little nob part moves in a circle. 


Reciprocating Rectilinear Motion
The bar at the bottom goes back and forth (linear). A perpendicular piece rocks side to side. That connects to a nub on the circular gear. It seems to slow down at the top and speed up at the bottom of the gear's motion. 

Rotary into Rectilinear Motion
This one is pretty cool because it looks like the components are playing game or they are in an assembly line or something. In the top, 2 nubs are attached to the circle and they spin. The hit the prongs coming out of the other parts and knock them away. 
In the bottom one, the triangle spins in the center and the prongs hit the corners of the surrounding piece moving it from side to side. This moves the whole axis left and right.