# basic physics unit 1

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• basic physics unit 1.1
• units and dimentions
• there are 6 base units that i need to know
• Kilogram Kg
• metre m
• second s
• ampere A
• kelvin K
• mole mol
• Homogeneous-units are equal on both sides of an equation
• SI units; divide by 1000 to increase eg. 1m to 0.001km and multiply by 1000 to decrease eg. 1g to 1000mg
• density
• density is constant and doesn't depend on the shape or size of the the sample of material
• the equation is p=m/v
• the units are kgm^-3
• moments
• definition= the moment of a force about a point is the product of the force and the perpendicular distance from the point to the line of action of the force
• moment F about P = Fd
• use this to work out moments
• the units are Nm
• the principle of moments= the sum of the clock wise = sum of the anti clock wise
• conditions of an equilibrium; no resultant moment and no resultant force
• use trig to work out moments
• single support problems; use trig
• two support problems; use the sum of ac= sum of cw ; take moments from s1 to find s2 and vice-versa
• scalars and vectors
• scalar= magnitude only vector= magnitude and direction
• to add vectors and find the resultant force use Pythagoras or simple trigonometry
• resolving vectors= use trigonometry
• centre of gravity
• the centre of gravity of a body is the point where the entire weight of the body can be considered to act
• for symmetrical bodies the centre of gravity must lie on any plane of symmetry