Forces, Density and Pressure Flashcards
Centre of gravity
the point at which the weight of the object may be considered to act
Centre of gravity vs centre of mass
centre of gravity:
depends on gravitational field
weight = mass x acceleration due to gravity
centre of mass:
does not depend on gravitational field
Moment
the turning effect of a force
moment = force x perpendicular distance
The principle of moments
for a system to be in equilibrium, the sum of clockwise moments should equal to the sum of anti clockwise moments about the same point
Couple
a pair of equal and opposite coplanar forces that act to produce rotation
Factors for a couple
- equal in magnitude
- opposite in direction
- perpendicular to the distance between them
Torque
the moment of a couple
equation for torque of a couple
torque of a couple = one of the forces x perpendicular distance between the forces
Equilibrium
all forces in a system are balanced. no resultant force, no resultant torque
Coplanar forces on equilibrium
- represented in closed vector triangles
- draw all the forces in a free body diagram
- remove the object and put all the forced coming from a single point
- rearrange the forces into a closed vector triangle, keeping the same length and direction
Density
the mass per unit volume of an object
p = m / v
Pressure
force per unit area
P = F / A
Hydrostatic pressure
the pressure that is exerted by a fluid at equilibrium at a given point within the fluid, due to the force of gravity
△P = pg△H
Atmospheric pressure
pressure we experience on the surface of the Earth due to the weight of the atmosphere pressure us to the Earth at right angles of every surface of our body
Total pressure
Total pressure = atmospheric pressure + hydrostatic pressure
