H1.04. 2022 Forces Notes

CJC H1 PHYSICS LECTURE NOTES JC1 2022 4(1) 4 Forces Main concept(s) 1. Meaning of force 2. Elastic force and Hooke’s law 3. Meaning and examples of contact force and non-contact force 4. Friction and viscous forces 5. Turning effects of a Force, moments and torque of a couple 6. Conditions for Equilibrium 7. Fluid (or hydrostatic) pressure 8. Upthrust, Archimedes’ Principle and Principle of Floatation Learning Outcome(s) 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 a mass, charge and current-carrying conductor 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 Introduction The concept of forces is fundamental in Physics and spans across many different topics. This chapter briefly overviews two broad categories of forces, namely contact and non-contact forces. Following that, a more in-depth study of some contact forces including resistive forces, elastic force, fluid pressure and upthrust is presented. You will also learn the turning effects of a force as well as the conditions for a system to be in equilibrium.

CJC H1 PHYSICS LECTURE NOTES JC1 2022 4(2) 1. 4.1 The Meaning of Force • A force is a push or pull. • Exists as a result of interaction between 2 bodies. • Whenever there is an interaction between two bodies, there is a force upon each of the bodies. • Force is a vector quantity that has both magnitude and direction. 1. 4.2 Broad categories of Forces All forces (interactions) between bodies can be placed into two broad categories: • Contact forces are those types of forces that result when the two interacting bodies are physically in contact with each other. • Non-contact forces are forces resulting from action -at-a-distance. These forces between two interacting bodies, which are able to exert a push or pull on each other despite their physical separation. Examples Contact forces Non-contact forces Friction Air Resistance Tension Applied Force Normal Contact Force Spring Force Gravitational Force Electrical Force Magnetic Force The usual abbreviation