# Additional science Phyisics , Edexcel revision notes

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• Created on: 01-05-13 17:41

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Static electricity
What it is?
A charge that is not free to move .This causes charge to
build in one place and it often ends up with a spark
when it moves.
Example of static electricity
Rubbing a rod (polythene and acetate rubbed with cloth)
What causes build up of Static electricity?
Friction
When two insulating materials are rubbed together the electrons get away from both materials and transferred into
the other materials.
Leave a +ve and ve charge.
Only ­ve electrons move but +ve charge is caused when an electron is lost.
Changing by induction
When a charged object is placed near an object with no
charge, it tends to induce charge because electrons from
an uncharged object either move away or towards the
charged object.
The new arrangement of charge will always pull two
objects together because the opposite charge attract.
More about static electricity
As charge builds up so does voltage causing sparks
The sparks can cause fire
Earthing is used to get rid of them
An object can be earthed by using a conductor.
Uses of static electricity
Paint is charged as it comes out of the nozzle
Opposite charges repel
Paint is spread out and attracted by the negatively charged object
While material is sprayed it is connected to earth
Advantages of spray paint
Less paint wasted
even coating
every part of the object gets painted.
Other uses
photocopiers
inkjet printers

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Dangers
Lightning ­ caused by static charge building in clouds, can damage buildings
Aircraft refuelling build up of charge can cause explosions (ignite fuel)
What causes opposite charges to attract?
Electric force field forces opposite charges to be pulled together.
Direct current = supplied by cells or batteries
Alternating current = supplied by generators.
Electric currents
Current ­ rate flow of charged particles
Voltage
a way of measuring the amount of energy transferred to a component by current .…read more

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Thermistors
hot conditions resistance drops
cool conditions resistance goes up
useful for temperature detectors
E.g. car engine temperature sensors & electrostatic thermostats
Current against pd graphs
Transferring energy
Calculating power
Calculating energy
Speed and velocity
both measured in m/s or mph or km/h
both say how fast you are going
Speed Velocity
How fast you are going with no regard to direction Tells how fast you are going to the direction of travel
(e.g. 30 mph) (e.g.…read more

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Acceleration & velocity time graphs
Acceleration
How quickly velocity is changing ­ this can be a change in speed or direction
Has size and direction
Vector quantity
Formula
Acceleration = change in velocity / time or acceleration (m/s) = (v-u)/t
Velocity-time graphs
Calculating distance travelled
The steeper the graph the greater the acceleration/deceleration
Gradient = acceleration
Area under graph= distance travelled
Flat section =steady speed
Steeper the graph , the greater the acceleration or deceleration
Uphill (/) acceleration
Downhill (\) deceleration
Curve= changing acceleration…read more

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Distance time graphs
Horisontal lines= stationary
Straight sloping lines =constant speed
The steeper the line the fatser the object is travelling
Speed can be calculated using gradient
Forces
The 6 types of forces
Gravity (weight)
Reaction force
Action force
Thrush (push or pull)
Drag
Lift
Tension
Force
Vector quaintly
Measured in Newtons ,N
Free -body diagram demonstrates forces on objects
Example of free-body fall diagram…read more

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Action and reaction force
Direction of forces must be taken to account
Newton's first and third law
1st law on motion states that if there is no resultant force then the force acting on the object then:
If stationary , the object will remain at rest
If moving , the object will keep moving at constant speed
3rd law
When two objects interact ,each object exerts an equal but opposite force on the other(action and reaction
forces)
Resultant force = The total force that results…read more

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If resultant force of an object is not zero then it will continue accelerating in the direction if the resultant force.
Force and acceleration
When resultant force is acting on an object the object will accelerate in the direction of the RF.
Size of acceleration depends on : size of force (for the same mass , the bigger the force , the bigger the
acceleration)
Mass of object (for the same force the more massive the object is the smaller the acceleration.…read more

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If there us an unbalanced force the object will accelerate in the direction of the force
Overall unbalanced force is called resultant force
Bigger force =greater acceleration
Bigger mass= smaller acceleration
Stopping distance = thinking distance + Braking distance
Thinking distance = distance travelled as driver reacts
Braking distance = distance travelled while the brakes are applied
Factors affecting thinking distance
reaction time increases
Speed of car
Reaction time increases when
Tired
Distracted
Poor eyesight
Under influence of drug and alcohol
Carelessness
Factors affecting Braking…read more

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The faster the momentum changes the more force on the object
The impact of force on an object can be reduced by increasing the time taken for the object to stop (Impact
time)
In a crash the following are used to reduce the impact force on the driver:
Seatbelts
Crumple zones
Air bags
Change in momentum
Force is needed to change momentum of an object.…read more

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KE= energy of movement
KE formula:
KE = ½ mxv2
Conservation of energy
Energy cannot be destroyed or created it can only be transferred into different form.
Braking distance & velocity of a vehicle
KE in a car can be transferred into heat energy by the brakes
In a car the braking force and mass are constant .this means the braking distance is directly proportional to
velocity 2
Doubling the velocity of car quadruples the braking distance.
Vectors and velocity
Magnitude= size e.g.…read more

## Comments

thank you and God bless **

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