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Module 3 - Chapter 4 - Forces in Action II - Coggle Diagram
Module 3 - Chapter 4 - Forces in Action II
Moments
Moment of a force is the turning effect of a force about some axis or point
Moment = Force x perpendicular distance of the line of actions of force
Principle of moments
When a body is in equilibrium, the net force acting on it is zero and its net moment is zero
For a body in rotational equilibrium, the sum of the anticlockwise moments about any point equals the sum of the clockwise moments about that same point
If the force is acting parallel to the pivot, it will not produce a moment
Couples
Two equal and opposite forces on an object that act a distance apart
Allows an object to spin without any translational motion
Two forces are parallel along different lines
Torque of a couple
The moment of a couple
One of the force x perpendicular separation of the forces
Creates rotational acceleration but not linear acceleration
Triangle of forces
Forces in equilibrium
Arrows are drawn to represent each of the three forces end-to-end
Triangle is clsoed because the net force is zero so the object is in equilibrium
Different ways of thinking
Resulatnt forces of two forces must be equal in magnitude to the third force, but in the opposite direction
Resultant force verticlly/ horizontally must be zero, so the resultant force can be resolved into its vertical and horizontal components
Coplanar forces
Coplanar forces are forces that lie in the same plane
If all three coplanar forces pass through a point in space, you can draw a triangle of forces for the forces plassing through that point
Density and pressure
Density
Mass per unit volume
Density = mass / volume
Determining density
Mass can be measured directly using a digital balance
For liquid, use a measuring cylinder for volume
Volume
Liquids - use measuring cylinder
Regular shaped solid - Use digital callipers to measure length, width and height
Irregular shaped solide = Use the volume of water the object displaces
Pressure
Normal force exerted per unit cross sectional area
Pressure = Force/ Area
Pressure in fluids
Gases and liquids are fluids
Fluids exert pressure do to the constant bombardment by their molecules
Pressure exerted by the earth's atomstphere is around 101kPa
Liquids
p = height x density x acceleration of free fall
Pressure at a particular depth is the same in all directions
Derivation
Upthrust
Buoyant force on a submerged object can be explpained in terms of the pressure difference at its upper and lower surface
Resultant force =
force at top =
Resultant force = force at the bottom - force at the top
Upthrust is equal to the weight (axp)g of the fluid displaced by the block of wood
x = height of object
Archimedes' principle - upthrust exerted on a body immersed in a fluid is equal to the weihgt of the fluid that the body displaces
mass = Axp (volume x density)
Force at bottom =
