2.1 Modelling the Motion of a ParticleA particle, in physics simulation terms, can be thought of as a point mass. The importantfact to note is that a particle has mass, but neglects the properties of volume and shape: asa consequence they are much simpler to simulate than a full body.2.1.1 Newtonian EquationsLet’s say that at a particular time a particle’s position and velocity are both known. SirIsaac Newton’s First Law of Motion states that from these properties, assuming theparticle is affected by no outside forces, the motion of the particle can be modelledforward in time indefinitely. If the velocity is zero the particle will simply remain still; if itis non-zero the particle will continue on at that velocity forever. This is described formallyby Newton’s First Law of Motion.“Every object in a state of uniform motion will remain in that state ofmotion unless an external force is applied to it.”Newton’s First Law of MotionFor a particle to change velocity therefore, a force needs to be exerted upon it. Bydefinition, this will cause the particle to accelerate (acceleration is defined as change invelocity over time). This is described more formally in Newton’s Second Law of motion.F = ma