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Moments and Pressure By Bethan Poole (5.4 Moments, levers and gears…
Moments and Pressure
By Bethan Poole
5.4 Moments, levers and gears
When a force causes an object to rotate about a pivot point, turning effect is called the moment of a force
If an object is balanced, total clockwise moment about the pivot equals the total anticlockwise moment about that pivot
F1 x d1= F2 x d2
Leavers and gears can be used to
transmit the rotational effects of forces
Magnify either the size of the applied force or the distance the force moves over
When the applied force moves further than the transmitted force, force is increased
When the applied force is bigger that the transmitted force, distance is increased
5.5 Pressure and pressure differences in fluids
5.5.1 Pressure in a fluid
Fluid can be a liquid or a gas
As particles move around in a fluid, they collide with the surface of objects in the fluid or the surface of the container
Collisions create a force normal (right-angle) to the surface
If the pressure acts on a bigger area, it will produce a larger force
5.5.1.2 Pressure in a fluid 2
Pressure at a point in the liquid is dependent on:
Height of column above a point
Density of liquid
The higher the column and the denser the liquid...
the greater the weight above the point
the greater the force on the surface at that point
the greater the pressure
Upthrust
When an object is submerged in a liquid there is a greater height of liquid above the bottom surface that above the top of the surface
Greater pressure at bottom that top- creates a resultant force upwards
The upward force is called upthrust
Objects float when weight is equal to upthrust and sink when weight is greater that upthrust
Object less dense than liquid
displaces a volume of liquid greater than its own weight so rises to surface
will float with some of the object remaining below surface
displaces liquid of equal weight to the object
Object with a low density, more will remain above surface
Object denser than liquid cannot displace enough liquid so sinks
No matter the density, the size of upthrust equals the weight of liquid displaced
Pressure higher at bottom of column as the particles above are exerting a force on the particles below it
5.5.2 Atmospheric pressure
Atmosphere- relatively thin layer of air around the earth
Greater the altitude, the less dense the atmosphere and the lower the atmospheric pressure
High altitude- less air above the surface than at lower altitude so smaller weight of air acting on the surface, therefore lower pressure