Vectors and Scalars
VECTORS contain magnitude and direction.
i.e momentum, acceleration, velocity, weight, force
SCALARS contain magnitude only.
i.e. time, density, speed, distance, energy. pressure
Newtons 3rd law
"If object A exerts a force on object B, then object B exerts an equal but opposite force on object A."
A moment is a turning effect of a force.
It can also be called a torque.
Moment = force X perpendicular distance from pivot
(Nm) (N) (m)
Principle of Moment
For a body to be in equilibrium:
- Sum of the clockwise = Sum of anticlockwise moments moments
Conditions for equilibrium
For an object to be in equilibrium:
- NO NET FORCE ACTING IN ANY DIRECTION
- NO NET TURNING EFFECT ABOUT ANY POINT
Centre of Gravity & Centre of Mass
Centre of Gravity of an object is the point at which we can take its entire weight to act.
Centre of Mass of an object is the point at which we can takes its entire mass to act.
When an object is outside the base it will topple.
The displacement of point B from point A is the shortest distance from A to B, together with the distance.
Mean Speed: total distance travelled / total time taken
Instantaneous Speed: rate of change of distance
Mean velocity: total distance/ total time taken
Instantaneous Velocity = rate of change of displacement
Mean Acceleration = change in velocity / time taken
Instantaneous Acceleration = rate of change of velocity
Terminal velocity occurs when the frictional force = driving force.
The driving force must be constant and the frictional force must increase with speed.
Graphs of terminal velocity
Work done = Force x Distance moved in direction of force
Work Done units are JOULES however its base units are Nm.
Area under a Force-distance graph = Work done
Work Done = Energy transferred
"Tension in the spring/wire is proportional to its extension from its natural length, provided the extension is not to great."
Stretching force (F) =spring constant (K) X extension (x)
The spring constant is sometimes called the stiffness.
Force extension graph.
Elastic potential energy = 0.5 X Stretching force X extension (AREA UNDER GRAPH)
Interchange between KE & PE
PE LOST = KE GAINED
Conservation of energy
"Energy cannot be created or destroyed only transferred from one for the another."
Gravitational potential energy = mgh
Kinetic energy =
Power is the rate of energy transfer.
Power = work done / time.
Power is measured in WATTS.
1 Watt = 1 joule per second
Static electricity is caused by the transfer of electrons for one object to another.
Neutral atoms can lose or gain electrons these atoms become positively or negatively charged.
These charged atoms are called ions.
GAIN ELECTRONS = - VE
LOSE ELECTRONS = +VE
Current = Rate of flow of charge
Charge = current X time
Charge is measured in Coulombs.
Derive I = nAve
Volume = Al
Number of free electrons per m = nAl
Charge = nAle
As current = charge/ time
As v = l/t
Therefore I= nAve
Conduction in Metals
Free electrons collide with lattice ions.
Kinetic energy is transferred from the electrons to the ions therefore energy is transferred.
What factors effect current?
(I = nAve )
- number of charge carriers per m
- cross sectional area of conductor
- The drift speed of the charge carrier
- Charge on an electron
What type of charge carriers carry electricity in a gas?
- Electrons and positive ions
Define A Volt
"The potential difference between 2 point in a circuit when 1 joule of work in transferring 1 coulomb of charge from 1 point to the other. "
Units: V = Jc
- Semi-conductor Diode
- filament lamp
- metal wire at constant temperature
"Voltage is proportional Current provided temperature is constant."
Ohms law graph
"Resistance of a conductor is the ratio of p.d applied across it, to the current passing through."
Resistance is measured in ohms ( ).
A superconductor is a material with zero resistance.
As there are no collisions in a superconductor there is no energy transferred therefore no heat lost.
For a material to become a superconductor must be cooled below its transition temperature.
To cool material use liquid nitrogen.
- Current is the same at all points
- Voltage splits
- R = R + R
- current splits up
- Voltage stays the same.
Emf = electromotive force
Emf is the total work done by a cell per unit charge
V = E -ir
V = energy delivered per unit charge to external circuit
E= energy supplied per unit charge to circuit from chemical energy of cell.
Ir= Energy lost in internal resistance