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Physics Unit 2
Descripción
Mapa Mental sobre Physics Unit 2, creado por Apoorva Sriram el 13/01/2015.
Mapa Mental por
Apoorva Sriram
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Apoorva Sriram
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Resumen del Recurso
Physics Unit 2
Forces and their effects
Resultant forces
Whenever two objects interact the forces they exert are equal and opposite
hand pushing on table= table pushing back
Lots of forces acting on one point
replaced by single force doing everything together
resultant force
may cause a change in the state of object
Forces and motion
Acceleration
a=f/m
m/s squared
determined by resultant force (N) and mass (kg)
the rate of change of velocity per unit of time
a= v1-v2/t
final velocity- initial velocity/ seconds taken
velocity/time graphs
Velocity = An objects speed in a certain direction
the steeper the gradient the greater the acceleration
a downward slope means constant decceleration
a flat line = constant velocity
distance = area of graph shape
m/s
Forces and breaking
when a car travels at a steady speed the driving force is balanced by resistive forces
therefore the resultant force is 0
when the breaks are applied
work done by the friction between the brakes and the wheels reduce the kinetic energy of the vehicle
the temperature of the breaks increase
Stopping distances
a drivers reaction time can be influenced by
tiredness
drugs
alcohol
a vehicles braking distance can be affected by
adverse road/weather conditions
poor condition of the vehicle
Forces and terminal velocity
the faster an object falls the greater the friction
Three stages of falling
An object falls b/c gravity and weight. There is no air resistance. There is a resultant force downwards
It gains speed, air resistance increases, there is a resultant force downwards.
The objects weight is balanced by the air resistance, no resultant force, the object reaches terminal velocity
w=m x g
N=kg x N/kg
Forces and elasticity
forces may change the shape of an object
a force applied to an elastic object will result in the object stretching and storing elastic potential energy
if an object returns to its original shape elastic potential energy is stored in the object when work is done on it
f = k x e
The Kinetic energy of objects speeding up and slowing down
Forces and Energy
work is done when a force causes an object to move through a distance
Joules
Energy is transferred when work is done
W = F x d
power = work done in a given time
P = E/t
the change in gravitational potential energy is what happens when something is raised
Ep = m x g x h
kinetic energy = 1/2 x mass x speed
joules/kg/ meters per second
Momentum
Momentum is the tendency of an object to carry on moving in the same direction
Momentum = mass x velocity
kg m/s
momentum is conserved
if nothing else acts on it the momentum stays the same through collisions and explosions
Currents in electrical circuits
Static electricity
When insulating materials are rubbed against each other they become electrically charged
Negatively charged electrons are rubbed of one material and onto the other
equal amounts of opposite charge
this only works for insulators
when two charged objects are brought together they exert a force on each other
electrical charges move better through other substances
e.g. metal
Electrical circuits
Electric current is a flow of charge
The size of the electric current is the rate of flow of electric charge
I = Q/T
Current = charge/time
amps = coulombs/ seconds
potential difference is the work done per coulomb of charge that passes between two points in a circuit
V = W/Q
potential difference = work done/ charge in coulombs
Current / potential difference graphs show that as current changes so does potential difference
V= I x R
Using Mains Electricity safely and the power of electrical appliances
Household electricity
direct current
current that always passes in the same direction
batteries, cells
alternating current
always changing direction
mains electricity
50 hertz
230 V
Electrical cables
2 or 3 inner wires
copper core
flexible plastic outer layer
Structure of a plug
If there is too much current
it is stopped by the fuse/ circuit breaker/ live wire
when there is too much current the fuse will melt and break the circuit
a residual circuit breaker will detect a difference in the current between the live and neutral wires
hey are faster than fuses
appliances with metal cases are usually earthed
the earth wire creates a safe route for the current to flow through
Current, charge and power
When an electrical charge flows through a resistor, the resistor gets hot
therefore energy is wasted
filament bulbs waste energy
The rate at which energy is transferred by an appliance is the power
power = current x potential difference
P = I x v
energy transferred = potential difference x coulombs
E = V x Q
power = energy/time
P=E/t
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