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
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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