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Home Education IGCSE IGCSE Physics : Topic 1 General Physics

# IGCSE Physics : Topic 1 General Physics

1.1- Measuring Time And Length

Measuring Length-Micrometer ( Use 10 sheets of paper for accuracy)

Measuring Time- E.g. : one swing of pendulum ( Find the times for 25 swings for accurate results)

Example of Scalar qualities-Time, Volume, Speed, temperature

Example of Vector qualities- Velocity, Change in Temperature, acceleration, force, momentum

1.2- Mass, weight, volume and density

Density= Mass/ Volume

Mass: the property of an object that is a measure of its inertia (a resistance to accelerate), the amount of matter it contains, and its influence in a gravitational field.

Weight is the force of gravity acting on an object, measured in Newtons, and given by the formula: Weight = mass × acceleration due to gravity

Measuring volume
Liquid- Level on the scale       Regular object(Square box) – Ruler
Irregular Object(Rock)- Lower into a partly filled measuring cylinder, Rise in level on the volume scale gives the volume of solid. Alternative method – Displacement Can (Fill water to level of spout, insert object, water displaced = volume of object)

1.3- Speed, velocity, Acceleration

Speed= distance/time

Acceleration= Change in velocity/ time taken

Velocity= Vector ( Magnitude + direction)      Speed= Scalar ( Magnitude only)

Distance Time Graph

Speed Time Graph
Gradient of graph= Acceleration                     Distance= Area under graph

Positive increase of speed= Acceleration       Negative increase of speed= Retardation

Acceleration of Free fall= gravitational field strength in Earth = 10

Terminal Velocity

Downward acceleration is caused by Gravitational field strength; Air resistance slow things down. Once air resistance is equal to Gravitational field strength, it is at terminal velocity ( Constant Velocity)

1.4- Forces

Hooke’s Law

The extension of an object is proportional to the load beneath its elastic limit.

Limit of proportionality= point at which load and extension are no longer proportional

Elastic limit= Spring will be permanently stretched

Newton’s first law of motion= If no external for is acting on it, an object will, if stationary, remain stationary, and if moving, keep moving at a steady speed in the same straight line

Newton’s 2nd law of motion: F = m × a -acceleration is proportional to the force, and inversely proportional to mass

Newtons 3rd law of motion: if object A exerts a force on object B, then object B will exert an equal but opposite force on object A

Centripetal Force and Centrifugal Force

Circular motions- An object at steady speed in a circular orbit is always accelerating as its direction is changing, but it gets no closer to the centre

Centripetal force- Force acting towards centre of circle

Centrifugal force- Force acting outwards the centre of circle.

Magnitude of centripetal and centrifugal is the same but direction is opposite

Centripetal force increase when mass, speed and radius increase

1.5- Turning Effects

Moment of a force= force x perpendicular distance from the point

Moments of a force are measured in Newton meters, can be either clockwise or anticlockwise.

Conditions of equilibrium= no net moments, sum of clockwise moment is equal to the sum of anticlockwise moment.

1.6 – Energy, Work and Power

Key terms and formulas: KE- 1/2MV^2               GPE- MGH

Law of conservation of energy- Energy cannot be made or destroyed, but it can change from one form to another.

Types of energy:

Energy Resources

Renewable source- Sources that won’t run out

Non-renewable source- Sources that would be extinct in a certain number of time

fuels can be burnt (or nuclear fuel can be forced to decay) in thermal power stations to transform the chemical energy stored to thermal energy which makes steam which turns turbines (kinetic energy) to produce electricity

hydroelectric dams: river and rain water fill up a lake behind a dam. As water rushes down through the dam, it turns turbines which turn generators

tidal power scheme: a dam is built across a river where it meets the sea. The lake behind the dam fills when the tide comes in and empties when the tide goes out. The flow of water turns the generator.

advantage: no greenhouse gases are produced

disadvantage: expensive, can’t be built everywhere

wave energy: generators are driven by the up and down motion of the waves at sea.

advantage: does not produce greenhouse gases

geothermal resources: water is pumped down to hot rocks deep underground and rises as steam.

advantage: no carbon dioxide is produced

disadvantage: deep drilling is difficult and expensive

nuclear fission: uranium atoms are split by shooting neutrons at them.

advantage: produces a lot of energy from using very little resources

solar cells: are made of materials that can deliver an electrical current when they absorb light energy solar panels: absorb the energy and use it to heat water

advantage: does not produce carbon dioxide

disadvantage: variable amounts of sunshine in some countries

Efficiency, Work and Power Formulas

Efficiency= useful work done/ total energy input

Work done= Force x Distance

Power= Work Done/ Time

1.7 – Pressure

Pressure = Force / area

To reduce pressure- Increase surface area of base

Pressure in liquid

Pressure= density x g(10) x height

Characteristic of pressure in liquids:
-Pressure acts in all directions
-Pressure increase with depth
-Pressure depends on the density of liquid
-Pressure doesn’t depend on the shape of the container

Pressure from the air

Barometers measure atmospheric pressure
, standard atmospheric pressure = pressure that supports a column of 760mm of mercury (101300 Pa)

Manometer measures pressure difference, height difference in manometer shows extra pressure. Actual pressure of gas supply = excess pressure + atmospheric pressure.

Gas Pressure and Volume

For a fed mass of gas at a constant temperature, the pressure is inversely proportional  to the volume. (Boyle’s Law)

Pressure and Volume are inversely proportional ( volume halves = pressure double)

P1V1=P2V2

Pressure x volume always has the same value 