Physics

Turning Effects of forces

Moment is produced

FORCE is applied onto an object with a pivot

Determined by two factors

magnitude of applied force

Perpendicular distance between the pivot and the applied force

Force x Distance

SI unit : Nm

Principle of moments

when an object is in equilibrium, the sum of clockwise moments is equal to the sum of anticlockwise moments about the same pivot

Centre of gravity

the whole weight appears to act from any orientation

Types of equilibrium

stable equilibrium

when the object is tilted slightly, the COG rises but falls back to its original position due to the moment produced by its weight about its contact point

Unstable equilibrium

Neutral equilibrium

when the object is slightly tiled, COG will fall and cause the object to topple due to the moment produced by its weight about the contact point C.

When the object is displaces, the COG will remain at the same level.

Energy, Work and Power

Energy

the capacity to do work

SI unit: joule

Work

Tyoes of energy

kinetic energy

potential energy

Electrical energy

Gravitational

Elastic

Light energy

Thermal Energy

Nuclear Energy

Sound Energy

Principal of conservation of energy

energy cannot be created or destroyed but can be converted from one form to another. The total energy in an isolated system is constant

Product the forces and the distance moved by the object in the direction of the force

W = F x S

SI Unit: Joule (J)

1/2(M)(V)^2

MxGxH

Power

Work/time

Energy/time

Si Unit: watt = J/s

Electricity and Magnetism

Electric Charge

if electrons are reomoved, the atom becomes positively charged

if the electrons becomes negatively charged

Like charges repel and

unlike charges attract

SI unit: coulomb (C)

Amount of charge carried by an electron (1.6 x 10^-19)

Electrical Conductors

Charged particles are free to move about

Electrical insulators

Charged particles are not free to move about

high ability to conduct electricity

low ability to conduct electricity

charged via induction

Electric field

Charged via rubbing (friction)

when 2 objects are rubbed together, electrons are transferred from the glass rod to the silk cloth

when the two metal spheres are touching each other and a negative charged rod is brought close to one of the spheres

the electrons in both spheres are repelled to the far end of the sphere who is further away from the rod and the sphere closer to the rod will have excess positive charges and the sphere further away will have excess negative charges

when both spheres are separated and the rod has been removed then both sphere will have in excess opposite charges.

bring a positively cahrged rod closer to the sphere, the positive charges will repel and move to the far end of the sphere

earth one side of the sphere and transfer the electrons away from the sphere

when u remove your hand and the rod, your sphere will only have negatively charged electrons which will redistribute and cause a the sphere to be negatively charged.

neutralisation

neutralisation

Earthing

Heating or in Humid Conditions

a region in which an electric charge experiences an electric force

the strength of the electric field is indicated by how close the field lines are to one another

Application of electrostatics

photocopier

Electrostatic precipitator

Spray Painting

Laser Printer

click to edit

Current of Electricity

Electric current

Current = Charge / time

Electromotive force

work done by the electrical energy source in driving a unit charge around a complete circuit

Electromotive force = Work done / Charge

potential difference

Result Electromotive force

Series

sum of all the cells

Parallel

one of the cell

Potential difference = work done / charge

used a voltmeter to measure

work done to drive a unit charge through the electrical component

Resistance

ratio of the potential difference across it to the current flowing through it

Resistance = Potential difference / Current

Si unit : ohm

Factors that affect the resistance

length

cross-sectional area or thickeness

type of material

Temperature

Ohm's law

current passing through a metallic conductor is directly proportional to the potential difference across it