Rigid Body Motion

• Of course bodies move both translationally and rotationally simultaneously.
• You can separate these forces.
• Size doesn't matter much when it comes to Newton. So, you can model using the Centre of Mass of an object (centre of gravity).
• For translational motion, even if the object is spinning, the object moves (via forces) in respect to the centre of mass.
• Calculating the centre of mass can be difficult, but for spheres of one substance it's easy.
• So, you can treat the object as a point.
• To combine translational and rotational, you typically use two coordinate systems.
• The translational system deals with the object moving.
• The rotaional system is usually centred on the center of mass.