4 - Definitions Flashcards
F = ma
Force = mass x acceleration
W = mg
The weight of an object is the gravitational force acting on the object.
Centre of of gravity/ centre of mass
They coincide. Imaginary point where all the objects weight appears to act.
Finding centre of gravity:
Suspend the object, it will come to rest with its centre of gravity vertically below its point of suspension.
Hang a plum line to draw a straight line.
Repeat.
Centre = point of intersection.
Terminal velocity
Speed = constant
In free fall, weight remains constant but drag force increases as the speed increases.
At the beginning of the fall there is no drag and accel = 9.81
As it falls speed increases and therefore, drag force does too.
Eventually the object reaches terminal v, when drag = weight.
Moment of a force
Moment = force x perpendicular distance of line of action of force from axis/ pivot.
SI unit for a moment
Nm
Principle of moments
Equilibrium
Net force = 0
Net movement = 0
Sum of anti-clockwise moments = sum of clockwise moments.
Torque of a couple
One of the forces x perpendicular distance = fx
Pressure
Force / Area
Upthrust
Is equal to the weight of the fluid displaced.
Volume of obj submerged x fluids density x 9.81
Density =
Mass / volume
SI of Density
kgm^-3
Pressure in vertical column of liquid =
Height of column x density of liquid x 9.81
