Dynamics JPJC Notes

1 JURONG PIONEER JUNIOR COLLEGE 9749 H2 PHYSICS DYNAMICS ______________________________________________________________________ Content (1) Newton's laws of motion (2) Linear momentum and its conservation Learning Outcomes Students should be able to: (a) state and apply each of Newton’s laws of motion (b) show an understanding that mas s is the property of a body which resists change in motion (inertia) (c) describe and use the concept of weight as the force experienced by a mass in a gravitational field (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 that 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 m omentum 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 closed system is always conserved in interactions between bodies, some change in kinetic energy usually takes place.

2 Introduction_________________________________________________________ If you see the velocity of an object change in either magnitude or direction, you know that something must have caused that change (or acceleration). An interaction that can cause an acceleration of a body is called a force, which is loosely speaking, a push or a pull on the body. The relationship between a force and the acceleration it causes was first understood by Isaac Newton (1642 – 1727). The study of the relationship is called Newtonian mechanics. We shall focus on its 3 primary laws of motion. Newtonian mechanics does not apply in the following situations:  When the speeds of the interacting bodies are very large (i.e. approaching the speed of light). In this case, Einstein’s special theory of relativity replaces Newtonian mechanics.  When the interacting bodies are on the atomic scale. In this case, Quantum mechanics replaces Newtonian mechanics. Physicists now view Newtonian mechanics as a special case of these two more comprehensive theories. Linking Kinematics and Dynamics In Kinematics, when we look at describing the motion of objects, we are concerned only with how the displacement, velocity and acceleration of the objects change with time. We then try to answer questions like: a) How far has the object moved from the starting/reference point? b) How long does the object take to move from