DHS 04 Forces (Lecture Notes)

DUNMAN HIGH SCHOOL 9749 H2 PHYSICS Year 5 (2024) TOPIC 4: Forces 1 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 taken 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 the definitions of pressure and density, the equation p= ρgh (k) solve problems using the equation p= ρgh (l) show an understanding of the origin of the force of upthrust acting on a body in a fluid (m) state that upthrust is equal in magnitude and opposite in direction 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 in magnitude and opposite in direction to the weight of the object to new situations or to solve related problems

2 Concept Map 1 Introduction One of the main goals of Physics has been to understand the immense variety of forces in the universe. 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

3 2 Types of Forces Learning Outcomes (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) In the past, we learn that a force is a push or a pull which one body exerts on another.