IGCSE Physics Revision Notes
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Unit 1 Measurements and units
G (Giga) 1,000,000,000
M (Mega) 1,000,000
K (Kilio) 1,000
D (Deci) .1
C (Centi) 0.01
M (Milli) 0.001
( Micro) 0.000001 1/1,000,000
N (Nano) 0.000000001 1/1,000,000,000
Volume and Density
Density= Mass/volume
Volume is in cubic meters M^3
Archimedes is the inventor of finding the density of an irregular shape by putting its in his bath tube
Unit 2 Forces and Motion
Speed
Speed= Distance moved/time taken
Eg. speed= 20m/2 s
Speed= 10m/s
Velocity is speed in a given direction
----------------------?
10m/s
Velocity with a magnitude is called a vectors
Final velocity = original velocity + extra velocity
Acceleration
Average acceleration= change in velocity/time taken
Eg 12ms/ 4s = 3m/s^2
Negative acceleration is called a deceleration or a retardation
Interpreting Motion graphs Check page 20 physics book
Equations of motion 4 golden equations (Page 22)
S=diplacement (m)
U= initial velocity (m/s)
A= Acceleration (m/s^2)
T= Time (s)
V= U + AT
S= UT + ½ AT^2
S= ½ (U+V) T
V^2= U^2 + 2AS
Free Fall
9.8 M/S^2 is the acceleration of free fall
Finding the gravity is
G= 2(h)/t^2 height and time
A force is a push or a pull by one object on another it has direction as well as magnitude (Size) so it’s a vector.
The SI unit is (N)
Check page 30 for forces and balance diagrams for every force there is an equal and opposite force
1st law of Newton Motion without a force is the first law of motion
An object in motion will stay in motion if no external force is acting on it, an object if in rest it will stay in rest if moving it will keep moving at a steady speed in a straight line.
Terminal velocity is similar to reaching an equilibrium which on earth is 60m/s because of gravity
Force, Mass and acceleration
This resistance to change in velocity is called inertia. The more mass something mass, the more inertia it has.
Resultant force is the addition of two or more forces on an object
Resultant force= Mass X Acceleration
F=MA (N) (KG) (M/S^2)
2nd law of Newton *Definition 1 Newton is the force required to give a mass of 1 kilogram an acceleration of 1m/s^2 *
Force Weight and gravity
Main features of gravitational force
All masses attract each other
The great the masses, the stronger the force
The closer the masses, the stronger the force
Weight is another name for the earths gravitational force on an object.
1 kg = 9.8 N ………………………….. 1kg ≈ 10 N
50kg = 500 N
Formula= weight = mass*gravity page 35
Action and reaction
3rd law of Newton
For every force there is an equal and opposite force
Rockets use the action and reaction principle it produces gas by burning fuel and oxygen made stored in small pellets and its pushes away through the action reaction force of exerting gas.
Vectors and scalar
Quantities such as force, which have a direction as well as magnitude (size) are called vectors
When adding two vectors you get a resultant
Scalars have a quantities such as mass and volume, which have magnitude but no direction are called scalars.
Adding vectors
Using soh cah toa you can find the resultant force by using the head to tail method and using the angle giving you can find the resultant force check page 38
In right angles you can easily use the Pythagoras theorem
Momentum
Momentum= Mass x Velocity
(Kg) (m/s)
Momentum is linked to the second law of Newton
Resultant force= Mass x acceleration
Resultant force = Change in momentum
(N) Time
Momentum 2
Trolleys and equal momentums
If two trolleys are stationary and are pushed of a the same time there momentum should be the same
Mass x Velocity to the left = mass x velocity to the right
(Trolley A) (Trolley B)
Linked to third law of Newton equal but opposite force trolley A is going in a negative direction while trolley B is going the other way negative direction
Law of conservation of momentum
When two or more objects act on each other their total momentum remains constant, provided no external forces are acting
Collision problem
Momentum + Momentum= Negative or positive velocity (left right)
(trolley A) (trolley B)
Moving in circles
The inward force to make a object move in a circle is called the centripetal force
The centripetal force is for example the tension in the string when swirling a ball around
More centripetal force is needed if;
The mass of the object is increased
The speed of the object is increased
The radius of the circle is reduced
Change in velocity can mean either a change in speed or a change in direction for the centripetal force
Unit 3 Forces and Pressure
Moment of a force (turning effects) page 50
Moment of a force about a point = Force x Perpendicular distance from the point (F) (N) (M)
“this can also be used to balance out a plank with a center support”
Principle of moments
If an object is in equilibrium :
The sum of the clockwise moments about any points is equal to the sum of the anticlockwise moments about the point
Finding the centre of gravity
Is the central point of an object at rest
States of equilibrium
Stable equilibrium- no matter how you tip it will return to its original position
Unstable equilibrium- The cone is balanced, but only briefly. Its pointed base is so small that the centre of gravity immediately passes beyond it
Neutral equilibrium- Left alone it stays where it is but when moved it stays in a new position, its centre of gravity is always over the point which is its ‘base’
Stretching and compressing
Springs and loads will have an equal relationship between extension and load, eg 1 Newton = 1 cm, 2 Newton = 2 cm
But when stretched to much it reaches an elastic limits and the spring will not return to its original position.
Hookes law
A material obeys hooke’s law if, beneath its elastic limit, the extension is proportional to the load.
Elastic objects return to its original position
Non-Elastic it does not return to its original position
Pressure
Pressure= Force / Area
(P) (N) (M^2)
Pressure = Pascal
1N/M^2= 1 Pascal
Pressure in liquids
Rules of pressure in open liquids
Pressure acts in all directions
Pressure increases with depth
Pressure depends on the density of the liquid
Pressure does not depend on the shape of the container
Pressure in liquids formula
Pressure= Density of water x gravity x height
Hydraulic machines page(60)
Hydraulic machines use liquids because
*Liquids are virtually incompressible- they cannot be squashed
* If a trapped liquid is put under pressure the pressure is transmitted parts of the liquid
Hydraulic machines are seen as force multipliers they will increase the force through the properties of liquids the equation for this is
Output force/ Input force = Output piston area / input piston area
Pressure from the air
Its pressure of air acts in all directions
Its pressure becomes less as your rise up through it
Air can be compressed unlike liquids
Barometers measure atmospheric pressure
Standard atmospheric pressure is 1 atmosphere = 100 000 Pa
Unit 4 Work and Energy
The SI unit of work is joule (J) 1 joule is equivalent to a force of 1 newton moves an object of 1 meter in the direction of the force
Work done = Force x distance moved
Forms of energy
Potential energy= Objects at rest having the potential to do work like a rubber band being stretched
Kinetic Energy= This is energy due to motion all moving objects have kinetic energy
Thermal Energy= Heat is also energy, when hot objects cool down, their atoms and molecules slow down and lose energy.
Chemical Energy- Energy released by chemical reactions like burning fuel or food or batteries.
Electrical Energy- In circuits, the current is a flow tiny charged particles called electrons.
Radiated Energy- Light and sound traveling in forms of waves have energy.
Nuclear Energy- Splitting of atoms release energy also known as nuclear energy
Energy transformation
When energy changes from one form to another energy is transferred for example from potential energy to kinetic energy
During each transformation the total amount of energy stays the same this is an example of the law of conservation of energy
* Energy cannot be made or destroyed but it can change from one form to another*
Energy can be wasted though
he
Work done = Energy transformed
Calculating potential energy other known as gravitational potential energy
Gravitational potential energy= Mass(Kg) x Height x Gravity = (J)
Calculating Kinetic Energy
Kinetic energy= ½ x Mass (Kg) x Velocity^2 (V^2)= (J) Joules
Friction and breaking
Friction prevents machinery from moving freely and heats up in the moving parts creating energy.
Efficiency and Power
Efficiency can be calculated like this = Useful work done / Energy input= x%
Power is the rate at which work is done the SI unit of power is watt (W)
Power= Useful work done / Time taken
Eg if an engine does 1000 joules of useful work in 2 seconds its power output is 500 watts
Efficiency can also be calculated by useful power output / Power input= Efficiency
Energy Resources
Can be classified as renewable and non-renewable resources
Renewable= Wood, wind turbines dams etc
Non-renewable= Coal, fuel, fossil fuels and natural gas
Renewable resources
Hydroelectric energy= Dams
Tidal energy= tide coming in and out through dams and lakes
Wind energy
Wave energy
Geothermal Energy= Steam comes from hot undergrounds springs
Solar Energy= Solar panels and sun
Biofuels= Fuels from plants and animals made from renewable resources
Machines and force multipliers Page 90
The lever= Force1 x distance1 = Force2 X Distance2
Machines in definition are force multipliers the output force is always more than the input force this can be done by simple machines such as the ramp and the lever and pulley’s or more complicated machines like gearboxes
Unit 5 Thermal Effects
Moving particles
Solids Tightly packed together all connected fixed shape and volume
Liquids Has a fixed volume but not shape and
Gases A gas has no fixed shape or volume moves freely but quite quickly and fills any space available
This movements are called the kinetic theory
The movements of the particles in solids and liquids and gases depends on the heat the warmer the faster the particles move
Temperature
The Celsius scale 0?c freezing 100? boiling of water
Absolute zero is at -273?C its when particles in solids liquids and gases cant move any slower the Kelvin is based on absolute zero
Thermal conduction page 102
Is when heat is traveled through objects by the quicker movement of the particles eventually heat up the entire object only in solids
Poor conductors are insulators, insulators stop from heat being lost this can be used to insulate houses to get less bills couple of ways of doing this is through a loft glass or mineral wool insulation in the loft wall cavity filled with plastic foam beads or mineral wool double glazed windows
Convection Page 104
Convection is the carrying of thermal energy and it takes place only in liquids and gases
In air warm air rises and cold air cools in a convectional current this can be seen as a cycle between land and sea
In Liquids Warm water rises and as its up high it starts to move and cool down again until its heated up again like a cycle
Thermal Radiation Page 106
Objects giving of heat is called thermal radiation
The amount of heat given of is calculated by the wave lengths the more wavelengths the higher the radiation
This also has to do with different emitters and absorbers
For example black absorbs heat
White emits and reflects heat
Greenhouses and solar panels use thermal radiation to trap heat and create higher yield or energy
Liquids and vapours
Evaporation when liquids turn into gas through the use of heat
Evaporation can be done more quickly through several ways
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