## Chapter Topics:

Types of forces
Centre of gravity
Turning effects of forces
Equilibrium of forces
Up-thrust

## Learning Objectives:

(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 center 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 up-thrust acting on a body in a fluid.

(m) State that up-thrust is equal in magnitude and opposite in direction to the weight of the fluid displaced by a submerged or floating object.

(n) Calculate the up-thrust in terms of the weight of the displaced fluid.

(o) Recall and apply the principle that, for an object floating in equilibrium, the up-thrust is equal in magnitude and opposite in direction to the weight of the object to new situations or to solve related problems.