speed/ velocity m/s, km/h · weight = mass × gravity . w = m x g . gravity (10n/kg) ... gravity o...
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Area cm², m²
Volume cm³, m³, litre (l), millilitre (ml)
Density kg/cm³, g/cm³
Force Newton (N)
Speed/ Velocity m/s, km/h
Acceleration m/s²
Mass kilogram (kg), gram (g)
Time second (s)
Length metre (m), kilometre (km), centimetre
(cm)
Temperature degrees Celsius (C°)
current ampere or amp (A)
1 km 1000m 100,000cm
1 tonne 1000kg 1000,000g
1 hour 60 minutes 3600 seconds
1 L 1000 ml 1000cm³
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Speed
o The rate of change in distance
o Is a scalar quantity
Velocity
o The rate of change in displacement
o Is a vector quantity
How to measure gradient:
Average Speed = Total Distance ÷ Total Time
Type d-t v-t a-t
Gradient Velocity Acceleration
Value Displacement Velocity Acceleration
Area Displacement
Gradient = Rise ÷ Run
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An object will have acceleration if:
The magnitude of velocity changes
The direction of motion changes
When describing velocity, a direction must be given.
Some objects only have two directions, e.g. backward, forward
When this happens, you can name the two directions „positive‟ and „negative‟ so that calculations
are simpler
Example:
A person drives at a velocity of 40 m/s North
He accelerates, increasing his velocity to 50 m/s North in 10 seconds
o V = 5 m/s North
o U = 4 m/s North
o Change in Velocity = 5 m/s – 4 m/s
= 1 m/s North
o T = 10 seconds
o Acceleration = 1 m/s North ÷ 10 s
= 0.1 m/s²
Example:
A ball drops and hits the ground at 5 m/s and bounces back at 3 m/s in 1 seconds
o Up = Positive
o Down = Negative
V = 3 m/s
U = -5 m/s
Change in Velocity = 3 m/s - (-5 m/s)
= 3 m/s + 5 m/s
o = 8 m/s Up
T = 1 seconds
Acceleration = 8 m/s Up ÷ 1 s
8 m/s² Up
Change in Velocity = New velocity measurement – Previous velocity measurement
Change in Velocity = V - U
Acceleration = Change in Velocity ÷ Time
Acceleration = (V - U) ÷ T
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Forces
A force is a push or a pull
A force is an action that can make another object change shape or change its velocity
A force is an action that can make another object accelerate
Are divided into two categories; Contact and Non-Contact
E.g. gravitational, electrostatic, twisting etc.
Friction is a contact force involving two bodies opposing each others motion
o E.g. the friction of the tyres of a car on the road cause the car to move slower
Gravitational force acts on falling objects. They reach a terminal velocity when the up
thrust is equivalent to the gravitational force.
o When objects fall, the force of gravity acts upon them
o As gravity increases, air pressure increases
o When air pressure is equal to gravity, the object travels in a straight line
o This is called terminal velocity
o This is the constant speed at which an object falls to earth
When force acts on an object, it causes the object to change the value of velocity and the direction
of movement.
EXAMPLES OF FORCE:
Weight:
The gravitational force from the earth
It acts vertically down
Normal Force:
Acts 90° to the surface
Is equal to weight
Friction Force:
Has the direction opposite to the direction of movement
Acts between two surfaces
Tension Force:
Acts against the deformation of a body
It takes place in a string or a rope
Drag Force:
Acts in the case of air resistance
It has the direction against motion
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Mass:
Is the amount of resistance an object has towards movement
Is defined as the amount of substance in an object
Force = mass × acceleration
F = m x a
Weight = mass × gravity
W = m x g
Gravity (10N/KG)
When force acts on an object, it causes the object to change the value of velocity and the direction
of movement.
EXAMPLES OF FORCE:
Weight:
The gravitational force from the earth
It acts vertically down
Normal Force:
Acts 90° to the surface
Is equal to weight
Friction Force:
Has the direction opposite to the direction of movement
Acts between two surfaces
Tension Force:
Acts against the deformation of a body
It takes place in a string or a rope
Drag Force:
Acts in the case of air resistance
It has the direction against motion
Stopping Distance
Stopping Distance = Thinking Distance + Breaking Distance
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Factors affecting thinking distance:
Thinking distance is the distance a car travels when the driver is reaction to a situation
o Alcohol
o Other drugs and some medicines
o Distraction (e.g. mobile phones)
o Speed
o Tiredness
Factors affecting braking distance
Breaking distance is the distance a car travels after the breaks have been applied
o Weather
o Condition of the road
o Speed
o Condition of tyres and breaks
Momentum = Force × Perpendicular Distance from the Pivot
Force x Distance = Force x Distance
40 Newtons x 6 Metres = 80 Newtons x 3 Metres
Moment
Is a turning force
When a force causes rotation about a pivot
When System is in Equilibrium
Clockwise Moment = Anticlockwise Moment
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Centre of Mass
o Centre of mass is a single point in a body where all the mass appears to be
Centre of Gravity
o Centre of gravity is a single point in a body where all the force of gravity appears to
act
Initial linear region of force-extension graph is associated with Hooke‟s
law
Extension is proportional to the force providing the elastic limit is not
exceeded
Astronomy
Astronomy is the study of natural celestial bodies.
Definitions:
Satellite o An object that orbits about a large mass
Natural satellites are generally called moons
Moons are found orbiting some planets o Moons do not produce light but reflects light
Artificial satellites are man-made devices sent into orbit for:
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Communication
Military purposes
Mapping
Planet o A spherical body orbiting a star
A planet does not produce light but reflects light
Star o Is a celestial body that produces energy by
nuclear reactions The sun is a star because it is a source of energy due to nuclear reactions
between hydrogen atoms that form helium
Solar System o Is a collection of planet and other celestial objects orbiting the sun
Sun Mercury Venus Earth Mars Jupiter Saturn Uranus Neptune Pluto Asteroids Comets
Comet o Is space debris made of rocks surrounded by ice o Spends a lot of time out of planetary system o Have highly eccentric elliptic orbits
The Haley‟s Comet has an orbital time of 76 earth years
Galaxy o Is a large collection of billions of stars orbiting around the centre made up of many
stars
Universe o All mass that exist in space including planets, stars and nebulae o A large collection of a billion galaxies
Gravity o Is a force of attraction between any two or more objects with mass
Larger objects have a stronger gravitational force than smaller objects
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The force of gravity has a smaller effect when objects are further away Larger masses have a stronger gravitational field
Causes the planets to orbit the sun
Causes the moon and artificial satellites to orbit the earth
Causes comets to orbit the sun
Astronauts on different planets:
Have the same mass o As their body does not physically change
Have different weights o As weight is subject to the force of gravity
Which is different on each planet
Orbital Speed = (2 x π x Orbital Radius) ÷ Time Period
V = (2 x π x r) ÷ t
Life Cycle of a Star
Large nebula rotates very quickly
Nebula contracts by gravitational force of each particle forming a star
Star burns for billions of years until all the nuclear reaction stops
o A small star ends up as a white dwarf
o A medium sized star (like the sun) will:
Expand to form a red giant when nuclear reactions stop
Red giant collapses, shrinking rapidly and then explodes
Super Nova 1
o Everything in the star is blown away across the
universe
After the super nova, the medium sized star is left as a
neutron star
o A large star will:
Expand to form a super red giant
When it exhausts its fuel, it collapses, shrinking rapidly and explodes
Super Nova 2
Finishes off as a very dense mass made of neutrons
Its gravity is so strong that light cannot escape
o It is called a black hole
Spring Tides
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When the moon is full or new, the gravitational pull of the moon and sun are combined
At theses times, the high tides are very high and the low tides are very low
Neap Tides
During the moon‟s quarter phases, the sun and moon work at right angles, causing bulges to cancel each other
The result is a smaller difference between high and low tides
Mass Kilogram (kg) Energy Joule (J)
Distance Metre (m) Speed Metre/second (m/s)
Acceleration Metre/second2 (m/s2) Force Newton (N) Time Second (s)
Power Watts (W)
Energy transfers in many ways such as:
Thermal (Heat)
Light
Electrical
Sound
Kinetic
Chemical
Nuclear
Potential (Kinetic, Elastic and Gravitational)
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Energy is conserved
Energy cannot be created or destroyed, only transferred.
Efficiency = Useful Energy Output ÷ Total Energy Input
Efficiency = Work ÷ Total Energy Input
Sankey Diagram
Energy transfer can take place in many ways such as:
Convection
o Heat transfers in liquids and gases
o Fluids (liquid or gas) become less dense when heated
The lower density makes the warm fluid rise and cold fluid move down
Conduction
o Energy transfers through solids
o Conduction occurs when there is contact
o In metals, conduction is due to free electrons
o Bad conductors are insulators
Radiation (Infra-Red Radiation)
o It is the way energy moves through space (vacuum)
o It travels as electromagnetic waves with a speed of 300,000,000 ms-1. [3x108 ms-1]
o It needs a medium to travel through
Energy Loss at Home – Insulation
Windows
o Needs double glazing
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Roof
o Fibre wool insulation
Gaps
o Draught excluders
Walls
o Cavity wall insulation
Marble/Stone floors
o Carpets
Work Done = Force x Distance Moved
W = F x d
Work done is always equal to energy transferred measured in Joules (J)
Work Done = Energy Transferred
Energy Transferred = Force x Distance Moved
Gravitational Potential Energy = Mass x Gravity x Height
GPE = m x g x h
Kinetic Energy = ½ x mass x speed2
KE = ½ x m x v2
Power is the rate of transfer of energy or the rate of doing work measured in Watts (W)
Power = Work Done ÷ Time Taken
P = W ÷ t
Energy transfers involved in generating electricity are:
Renewable sources of energy:
o Wind
o Water
o Geothermal Resources
o Solar Heating Systems
o Solar Cells
Non-Renewable sources of energy:
o Fossil Fuels
o Nuclear Power
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Density
Measure of mass per unit volume for any substance
KG / M³
Density = Mass ÷ Volume
D = m ÷ V
Pressure
Measure of force per unit area
N / M²
Pa
Pressure = Force ÷ Area
P = F ÷ a
Pressure in liquids and gases
Pressure = Density x Height x Gravity
P = D x h x g
Density of some substances:
Pure Water
o 1000 kg/m³
Air
o 1.2 kg/m³
Atmospheric Pressure
100 000 N/m²
Temperature Celsius (0C) Kelvin (K)
Force Newton (N) Pressure Pascal (Pa)
Newton/ metre² (N/m²) Density Kilograms/metre³ (kg/m³)
Grams/millilitre (g/ml) Grams/centimetre³ (g/cm³)
Distance Metre (m) Area Metre² (m²)
Energy Joule (J) Mass Kilogram (Kg) Speed Metre/second (m/s)
Acceleration Metre/second² (m/s²)
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Brownian Movement
Brown observed pollen grains moving around randomly in water
He concluded that water particles were colliding with pollen grains and causing random
motion
Brownian movement also supported the idea that gas particles are also moving in random
motion in all directions with a range of speeds
Assumptions of Kinetic Theory of Gases:
Particles are points
Particles are more in straight lines between collisions
Collisions are elastic (bounce back with same speed)
Many particles, lots of space
Continuous random motion
Boyles Law
For a fixed mass of gas, the pressure is inversely proportional to the volume if the
temperature remains constant
Pressure is inversely
proportional to volume
Pressure is proportional
to the inverse of volume
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Charles Law
For a fixed mass of gas, the volume is proportional to the absolute temperature if the
pressure remains constant
Pressure Law
For a fixed amount of gas, the pressure is proportional to the absolute temperature if the
volume remains constant
° Celsius Kelvin
-273 0
0 273
100 373
As temperature increases, the speed of molecules increases
Pressure 1 x Volume 1 = Pressure 2 x Volume 2
P1 x V1 = P2 x V2
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Transverse Waves
A transverse wave is one that vibrates, or oscillates, at right angles to the direction in which
the energy or wave is moving
Longitudinal Wave
A longitudinal wave is one in which the vibrations, or oscillations, are along the direction
in which the energy or wave is moving
Transverse Waves Longitudinal Waves
Waves Inside Fluids Surface Waves
Shock Waves Electromagnetic Waves
Seismic Waves (Underground Waves) Seismic Waves (Surface Waves)
Sound Waves Light Waves
Degree (0) Frequency Hertz (Hz)
Force Metre (m) Speed Metre/second (m/s) Time Second (s)
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Amplitude
The maximum movement of particles from their resting position caused by a wave
Unit: A
Frequency
The number of waves produced each second by a source, or the number passing a
particular point each second
Unit: Hz (Hertz, 1 ÷ s )
Wavelength
The distance between a particular point on a wave and the same point on the next wave
(for example, from crest to crest)
Unit: λ (in metres, m )
Period
The time it takes for a source to produce one wave
Unit: T (in seconds, s )
Waves are a means of transferring energy from place to place, without the transfer of matter
Wave Speed = Frequency × Wavelength
v = f × λ
Wave speed is measured in metres per second ( m ÷ s )
Frequency = 1 ÷ Time Period
f = 1 ÷ t
Law of reflection states that the angle of incidence is equal to the angle of reflection when light
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Luminous Objects
Objects that emit their own light
E.g.
o Sun
o Stars
o Fire
o Light bulbs
Non-Luminous Objects
Objects that that do not emit light
We can see them because of the light they reflect
Virtual Images
Images though which rats of light do not actually pass
Real Images
Images created with rays of light actually passing through them
Properties of an image in a plane mirror:
The image is as far behind the mirror as the object is in front
Te image is the same size as the object
The image is virtual – that is, it cannot be produced on a screen
The image is lateral invested – that is, the left side and right side of the image appear to be
interchanged
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Medium
A material through which light can travel
Speed of light:
In a vacuum and in air
o 300 000 000 m/s
In water:
o 200 000 000 m/s
Refraction
Is a property of waves changing speed (and direction) when passing a boundary
Snell‟s Law:
States that the ratio of sine angle incidence and sine angle refraction is a constant for a boundary
between two materials
n = Sin i ÷ Sin r
Refractive Index = Sin (Angle of Incidence) ÷ Sin (Angle of Refraction)
Total Internal Reflection:
Is an optical phenomenon where light (waves) refract and reflect back at a boundary www.ch
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Critical Angle:
Is the angle where light reflects back and refraction is along the boundary
Sin C = 1 ÷ n
Sin (Critical Angle) = 1 ÷ Refractive Index
Reflectors
Use tiny prisms in their construction
The optical material is plastic – lighter and less fragile then a mirror
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Speed of sound depends on the air (gas) temperature (since particles may be closer when
gas is cooler)
Average speed of sound in air is approximately 340 m/s
Average speed of sound in seawater is approximately 1500 m/s
Average speed of sound in a solid is approximately 5000 m/s
Audible Range for:
Humans:
o 20 Hz – 20 000 Hz
Dogs, dolphins and bats:
o Over 20 000 Hz
Infrasounds
Sounds that cannot be heard by human beings as they are produced by objects that vibrate
at frequencies lower than 20 Hz
Ultrasounds
Sounds that cannot be heard by human beings as they are produced by objects that vibrate
at frequencies higher than 20 000 Hz
Loudness
Is the measure of the power of a sound
o A wave with a big amplitude is loud
o A wave with a small amplitude is soft
Echo
A reflected sound
Echo Sounding
When ships use echoes to discover the depth of the water beneath them
Pitch
The frequency of sound waves
Measuring the Speed of Sound:
Using echoes
o (2 x distance between presentation of sound and large blank wall) ÷ time between
presentation of sound and presentation of echo
Using an oscilloscope
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Current (I) Ampere (A) Charge (Q or q) Coulomb (C)
Energy (E) Joule (J) Resistance (R) OHM (Ω)
Time (t) Second (s) Voltage (V) Volt (V) Power (P) Watt (W)
Live Wire
Provides the path along which the electrical energy from the power station travels
Is alternately positive and negative causing alternating current (ac) to flow along it
Brown in colour
Neutral Wire
Completes the circuit
Blue in colour
Earth Wire
Usually has not current flowing through it
Is there for protection if an appliance develops a fault
Green and yellow in colour
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Hazards of Electricity:
Frayed cables
Long cables
Damaged plugs
Water around sockets
Pushing metal objects into sockets
Safety Devices:
Fuses
o Usually in the form of a cylinder or cartridge
o Contains a thin piece of wire made from a metal that has a low melting point
If too large a current flows in the circuit, the fuse wire becomes very hot and
melts
The fuse „blows‟, shutting the circuit off
Prevents shock and reduces possibility of an electric fire
o The correct fuse to use is one that allows the correct current to flow but blows if the
current is a little larger
Trip Switches or Circuit Breakers
o If too large a current flows in a circuit, a switch opens making the circuit
incomplete
o Once the fault in the circuit is corrected, the switch is reset, usually by pressing a
reset button
Does not need to be replaced
Earth Wires
o Provides a low-resistance path for the current if and when the live wire becomes
frayed or breaks and comes into contact with the metal casing
o Prevents severe electric shock as electricity passes through a person to the earth
Double Insulation
o Is when all electrical parts of an appliance are insulated with non-conductors so
that they cannot be touched by the users
o Appliances that have this do not require an earth wire
Heating elements are designed to have a high resistance
As the current passes through the element, energy is transferred and the element heats up
E.g.
o Toaster
o Kettle
o Dishwasher
o Cooker
Resistance prevents the flow of current, and causes an increase in temperature by doing so
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Power = Current x Voltage
P = I x V
Energy = Power x Time
E = P x t
Energy = Current x Voltage x Time
E = I x V x t
Alternating Current (ac)
The flow of electricity is constantly changing direction
Direct Current (dc)
The flow of electricity is always in the same direction
Electric Current
A flow of charge
Good Conductor of Electricity
A material through which electrons flow easily
o Electrons carry charges
Insulators
A bad conductor of electricity
Used to prevent the flow of charge
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Current is the rate of flow of charge
Charge = Current x Time
Q = I x t
Ammeter
Used to measure the size of the current flowing in a circuit
Voltmeter
Used to measure voltage
Battery
Consists of several cells connected together
Provides current flowing in one direction (dc)
Light Emitting Diode (LED)
Fitted to many appliances to show when the appliance is switched on or on standby
Glows when current is flowing through it
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Series Circuit
No branches or junctions
One switch can turn all the components on and off together
If one bulb (or other component) breaks, it causes a gap in the circuit and all of the other
bulbs will go off
The voltage supplied by the cell or mains supply is “shared” between all the components
o The more bulbs added, the dimmer they all become
o The larger the resistance of the component, the bigger its „share‟ of the voltage
Parallel Circuit
Have branches or junctions
Switches can be placed in different parts of the circuit to switch each bulb on and off
individually, or all together
If one bulb (or other component) breaks, only the bulbs on the same branch of the circuit
will be affected
Each branch of the circuit receives the same voltage
o Even if more bulbs are added, they all stay bright
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Resistance
Is a measure of energy dissipated by charge when unit current flows
All components offer some resistance to the flow of charge
o Some circuits allow charges to pass through them very easily losing very little
energy
i.e. the components have a very low resistance
o Some circuits do not allow charges to pass through them as easily and hence lose a
significant amount of energy
i.e. the components have a very high resistance
The energy is converted into other forms, usually heat
Voltage = Current x Resistance
V = I x R
Combine Series Resistance
R = R1 + R2 +.... Rn
Combined Parallel Resistance
1 ÷ R = (1 ÷ R1) + (1 ÷ R2) +.... (1 ÷ Rn)
Series Parallel
Voltage Divides Same
Current Same Divides
Combined Resistance High Low
Fixed Resistors
Included in circuits in order to control the sizes of currents and voltages
Variable Resistors
Allows the resistance to be altered
Thermistors
A resistor whose resistance changes quite dramatically with temperature
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o Resistance decreases as temperature increases
o E.g.
Fire alarms
Thermostats
Light-Dependant Resistors (LDRs)
Used in light sensitive circuits
o Resistance increases as light exposed increases
o E.g.
Photographic equipment
Automatic lighting controls
Burglar alarms
Diodes
A resistor that behaves like a one-way valve or one-way streets
Resistance is low to current flowing in a particular direction
Resistance is high to current flowing in the opposing direction
o Used in circuits where it is important that current flows only in one direction
o E.g.
Rectifier circuits that convert alternating current into direct current
Light Emitting Diodes (LEDs)
Diodes that glow when a current is flowing through them
OHM‟s Law
The current that flows through a conductor is directly proportional to the potential difference
across its ends, provided its temperature remains constant
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