TJC Unit 3 Motion & Forces

1 i Unit 3: Motion & Forces Learning Outcomes Students should be able to: (a) show an understanding of and use the terms position, distance, displacement, speed, velocity and acceleration. (b) use graphical methods to represent distance, displacement, speed, velocity and acceleration. (c) identify and use the physical quantities from the gradients of position-time or displacement-time graphs, and areas under and gradients of velocity-time graphs, including cases of non-uniform acceleration. (d) derive, from the definitions of velocity and acceleration, equations which represent uniformly accelerated motion in a straight line. (e) solve problems using equations which represent uniformly accelerated motion in a straight line, e.g. for bodies falling vertically without air resistance in a uniform gravitational field. (f) show an understanding that mass is the property of a body which resists change in motion (inertia). (g) define and use linear momentum as the product of mass and velocity. (h) state and apply each of Newton’s laws of motion: 1st law: a body at rest will stay at rest, and a body in motion will continue to move at constant velocity, unless acted on by a resultant external force; 2nd law: the rate of change of momentum of a body is (directly) proportional to the resultant force acting on the body and is in the same direction as the resultant force; and 3rd law: the force exerted by one body on a second body is equal in magnitude and opposite in direction to the force simultaneously exerted by the second body on the first body. (i) recall the relationship that resultant force 𝐹 = 𝑚𝑎 for a body of constant mass, and use this to solve problems. Name : ________________________________ Class : _________

2 1 Introduction Kinematics is the study of objects in motion. Motion occurs all around us. We see it in the everyday activity of people, of cars on the expressway, of javelins thrown by sportsmen, and even in the motion of comets. In Kinematics, we describe motion in terms of space and time while ignoring the agents that caused that motion. In the later part of this unit, we study the effects of forces on the motion of bodies. 2 Definition of quantities LO(a) 2.1 Position, Distance and Displacement Position is defined as the location of the object at any given time. For one-dimensional motion, we often choose the x axis as the line along which the motion takes place. Then the position of the object at any moment is given by its x -coordinate. If the motion is vertical, as for a dropped object, we usually use the y axis. Consider a particle, P, moving from position A to position B. • Dotted lines represent the path taken by the particle P. • The distance travelled by P between points A and B is the length of