ch 4 forces

field of force

a region of space in which a force acts on a body

centre of gravity

of a body is the single point at which the whole weight of the body may be considered to act

friction

force that opposes reactive motion between surfaces in contact

Hooke’s Law

states that the extension of a body is proportional to the applied force, provided that the limit of proportionality is not exceeded

formula for Hooke’s Law

F=kx

translational equilibrium

sum of forces acting on the object in any direction is zero

moment of a force

about a point is the product of the force and the perpendicular distance of the line of action of the force to the pivot

torque of a couple

is the product of one of the forces and the perpendicular distance between the forces

rotational equilibrium

no resultant force about any point

principle of moments

states that for an object to be in rotational equilibrium, sum of clockwise forces about any point must be equal to the sum of anti-clockwise moments about the same point

a body is in equilibrium when

1. sum of forces acting on the body in any direction is zero

2. sum of moments of the forces acting on the body about any point much be zero

pressure

is the force acting normally (perpendicularly) per unit area of a surface

upthrust

the net upwards force exerted by a fluid on a submerged or floating object. It arises due to the difference in pressure between the upper and lower surfaces of the object