ASRJC Dynamics Notes

ANDERSON SERANGOON JUNIOR COLLEGE PHYSICS 9749 / 8867 1 Additional Notes Topic 3: Dynamics Content: • Newton’s laws of motion • Linear momentum and its conservation Learning Outcomes: Candidates should be able to: Newton’s laws of motion (a) state and apply each of Newton’s laws of motion. (b) show an understanding that mass is the property of a body which resists change in motion (inertia). (c) describe and use the concept of weight as effect of a gravitational field on a mass. Linear momentum and its conservation (d) define and use linear momentum as the product of mass and velocity. (e) define and use impulse as the product of force and time of impact. (f) relate resultant force to the rate of change of momentum. (g) recall and solve problems using the relationship F = ma, appreciating the resultant force and acceleration are always in the same direction. (h) state the principle of conservation of momentum. (i) apply the principle of conservation of momentum to solve simple problems including inelastic and (perfectly) elastic interactions between two bodies in one dimension. (knowledge of the concept of coefficient of restitution is not required.) (j) show an understanding that, for a (perfectly) elastic collision between two bodies, the relative speed of approach is equal to the relative speed of separation. (k) show an understanding that, whilst the momentum of a system is always conserved in interactions between bodies, some change in kinetic energy usually takes place.

ANDERSON SERANGOON JUNIOR COLLEGE PHYSICS 9749 / 8867 2 Additional Notes Introduction • In Kinematics, we described motion in terms of position, velocity and acceleration without considering what might cause that motion. • In Dynamics, we consider the cause – what might cause one object to remain at rest and another object to accelerate? The two main factors are the mass of the body, and the forces acting on the body. Dynamics is therefore a study of the relationship between the forces acting on a body and the motion of that body. • The study of dynamics is largely governed by Newton’s Three Laws of Motion. A.1 Newton’s 1st Law • Newton’s 1st Law is also known as the law of inertia. • The inertia of a body is the property of a body to resist a change in its motion. • The mass of a body is a measure of the resistance of a body to a change in its motion i.e. a measure of its inertia. • The greater the mass of a body, the lesser the body accelerates under the action of a given applied force. • Unlike weight (see side note) which depends on gravitational field and therefore varies from place to place, mass is independent of gravitational forces, i.e. the mass of a body is the same on the Earth as on Moon. Mass is a scalar quantity while weight is a vector. Newton’s First Law (Law of inertia): A body stays at rest or continues to move with constant velocity unl