Solution:

• A mechanical system can include either a single object (for instance, an engine’s piston) or multiple objects that are connected (the entire engine).

Particles:

• When the physical dimensions are unimportant with respect to calculating forces, the object is called a particle.

• This concept idealizes the system as being concentrated at a single point rather than being distributed over an extended area or volume.

• Particle analysis will only have to consider the forces acting on the body and translational motion because rotation is not considered for particles.

• For the purposes of solving problems, a particle can be treated as having negligible dimensions.

Rigid bodies:

• On the other hand, if the length, width, and breadth of an object are important for the problem at hand, it is called a rigid body.

• As an example, when looking at the motion of a communications satellite as it orbits the Earth, the spacecraft can be regarded as a particle because its dimensions are small compared to the size of the orbit.

• However, when the satellite is being launched and engineers are interested in the aerodynamics and flight characteristics of the rocket, the launch vehicle would be modelled as a rigid body.

• Figure illustrates the conceptual distinction between forces applied to a particle and to a rigid body. You can see how a force imbalance could cause the rigid body, but not the particle, to rotate.