Understand and use Newton's third law; equilibrium of forces on a particle and motion in a straight line (restricted to forces in two perpendicular directions or simple cases of forces given as 2-D vectors); application to problems involving smooth pulleys and connected particles; resolving forces in 2 dimensions; equilibrium of a particle under coplanar forces.
Connected particle problems could include problems with particles in contact e.g. lift problems.
Problems may be set where forces need to be resolved, e.g. at least one of the particles is moving on an inclined plane.