# General Planar Motion

### Constraints

Many mechanisms that you will see in real life have constrained motion. Motion is constrained when the mechanism is forced to move in a particular way.

Examples of machines that exhibit constrained motion:

• Train on a train track.
• An engine piston.
• A car must follow the ups and downs of a road.

### Linear bearings / collars

Linear bearings and collars are sleeves that fit around or on shafts. They constrain motion to be in the direction of the shaft.

A good example of a machine with linear bearings is an exercise machine.

### Slots

A slot constrains the motion of a pin, for example, to move in the direction of the slot.

An example of a slot constraint is a Geneva wheel. A Geneva wheel changes continuous rotary motion to periodic motion.

### Joints

Joints can restrict the motion of mechanisms to which they are attached.

### Surface contacts

Surface contacts constrain the motion of some point on the rigid body to the profile of the surface, such as a car on a road.