H204 Forces - 1. Notes (1718) [For Upload]

9749 H2 Physics Lecture Notes Topic 4: Forces Page 1 of 20 Topic 4 Forces Content  Types of force  Centre of gravity  Turning effects of forces  Equilibrium of forces  Upthrust Learning Outcomes Candidates should be able to: (a) recall and apply Hooke’s law (F = kx, where k is the force constant) to new situations or to solve related problems. (b) describe the forces on mass, charge and current in gravitational, electric and magnetic fields as appropriate. (c) show a qualitative understanding of normal contact forces, frictional forces and viscous forces including air resistance. (No treatment of the coefficients of friction and viscosity is required). (d) show an understanding that the weight of a body may be take n as acting at a single point known as its centre of gravity. (e) define and apply the moment of a force and the torque of a couple. (f) show an understanding that a couple is a pair of forces which tends to produce rotation only. (g) apply the principle of moments to new situations or to solve related problems. (h) show an understanding that, when there is no resultant force and no resultant torque, a system is in equilibrium. (i) use a vector triangle to represent forces in equilibrium. (j)* derive, from definitions of pressure and density, the equation p = gh. (k)* solve problems using the equation p = gh. (l)* show an understanding of the origin of the upthrust acting on a body in a fluid. (m)* state that upthrust is equal to the weight of the fluid displaced by a submerged or floating object. (n)* calculate the upthrust in terms of the weight of the displaced fluid. (o)* recall and apply the principle that, for an object floating in equilibrium, the upthrust is equal to the weight of the object to new situations or to solve related problems. * Not required for 8867 H1 Physics

9749 H2 Physics Lecture Notes Topic 4: Forces Page 2 of 20 4.0 Introduction One of the main goals of Physics has been to understand the immense variety of forces in the universe in terms of the fewest number of fundamental laws. Today, all forces are understood in terms of just four fundamental interactions as follows: Force Effects Range/m Gravitational Force Weakest. Acts on all masses infinite Electromagnetic Force Acts on electric charges infinite Strong Nuclear Force Holds protons and neutrons together in a nucleus 10-15 Weak Nuclear Force Causes radioactive decay processes. 10-17 A force is a push or pull exerted by one body on another. It is an interaction between two bodies or between a body and its environment . Force is a vector quantity and hence it is quantified by having both a magnitude and a direction. The unit of force is newton (N). 1 N is defined as the magnitude of a force that accelerates a mass of 1 kg at a rate of 1 m s-2 in the direction of the force.

9749 H2 Physics Lecture Notes Topic 4: Forces Page 3 of 20 4.1 Types of Forc