3.2: Forces in action Flashcards
Archimedes’ principle
The upwards force acting on an object submerged in a fluid, is equal to the weight of the fluid it displaces.
Centre of gravity
The single point through which the object’s weight can be said to act.
Centre of mass
The single point through which all the mass of an object is said to act
Couple
Two equal and opposite parallel forces that act on an object through different lines of action. It has the effect of causing a rotation without translation.
Density
The mass per unit volume of a material
Drag
The frictional force that an object experiences when moving through a fluid.
Equilibrium
For an object to be in equilibrium, both the resultant force and resultant moment acting on the object must be equal to 0.
Friction
The resistive force produced when there is relative movement between two surfaces.
Moment of force
The product of a force and the perpendicular distance from the line of action of the force to the pivot.
Newton
The unit of force
Newton’s second law
The resultantforce acting on an object is equal to the rate of change of momentum of the object. It is also expressed as the net force acting on an object equaling the product of the object’s mass and acceleration. F = ma
Normal contact force
The reaction force between an object and surface.
Pressure
The force that a surface experiences per unit area. It is measured in Pascals (Pa)
Principle of moments
For an object to be in equilibrium, the sum of the clockwise moments acting about a point must equal to the sum of the anticlockwise moments acting about that point.
Tension
The result of two forces acting on an object in opposite, outwards directions.
