CIE Physics IGCSE
CIE Physics IGCSE
CIE Physics IGCSE
● A ruler (rule) is used to measure the length of an object between 1mm and 1m.
● The volume of an object of irregular shape can be measured by placing it into a measuring
cylinder full of water. This causes the water level to rise, and this rise is equal to the volume
of the object.
● A micrometer screw gauge is used to measure very small distances that a rule
cannot measure.
● Analogue and digital clocks and devices are used to measure time intervals.
● An average value for a small distance and for a short time interval can be found by
measuring multiples (including the period of a pendulum).
Motion
● Speed is defined as the distance traveled per unit time. If the speed of something is
changing, it is accelerating. The acceleration of free fall near to the Earth is constant.
𝑡𝑜𝑡𝑎𝑙 𝑑𝑖𝑠𝑡𝑎𝑛𝑐𝑒 𝑑
● 𝑎𝑣𝑒𝑟𝑎𝑔𝑒 𝑠𝑝𝑒𝑒𝑑 = 𝑣=
𝑡𝑜𝑡𝑎𝑙 𝑡𝑖𝑚𝑒 𝑡
● Distance is measured in mm, cm, m or km and time measured in ms, s, minutes or hours.
Remember to convert units to make sure everything is equivalent! For example if distance
𝑑𝑖𝑠𝑡𝑎𝑛𝑐𝑒
is in 𝑘𝑚 and time is in ℎ𝑜𝑢𝑟𝑠, then calculate and 𝑡𝑖𝑚𝑒 × (60 × 60)to get everything
1000
in metres and seconds.
● Velocity is the speed in a given direction.
𝒄𝒉𝒂𝒏𝒈𝒆 𝒊𝒏 𝒗𝒆𝒍𝒐𝒄𝒊𝒕𝒚
● Acceleration is the rate of change of velocity: 𝒂𝒄𝒄𝒆𝒍𝒆𝒓𝒂𝒕𝒊𝒐𝒏 = 𝒂=
𝒕𝒊𝒎𝒆
𝒗−𝒖
𝒕
In a distance-time graph:
In a speed-time graph:
Mass:
● Mass is a measure of how much matter is in an object.
● It is a property that resists change in motion.
Weight:
● Weight is a gravitational force (the effect of a gravitational field on a mass) measured in
Newtons: 𝑤𝑒𝑖𝑔ℎ𝑡 = 𝑚𝑎𝑠𝑠 × 𝑔𝑟𝑎𝑣𝑖𝑡𝑎𝑡𝑖𝑜𝑛𝑎𝑙 𝑓𝑖𝑒𝑙𝑑 𝑠𝑡𝑟𝑒𝑛𝑔𝑡ℎ = 𝑚𝑔
● The gravitational field strength on Earth is 10Nkg -1.
● Weights (and hence masses) can be compared using a balance.
Acceleration in free fall is due to gravity, and is the same as g, i.e. 10𝑚𝑠 −2
Density
𝑚𝑎𝑠𝑠 𝑚
● The density is defined as the mass per unit volume: 𝑑𝑒𝑛𝑠𝑖𝑡𝑦 = 𝑣𝑜𝑙𝑢𝑚𝑒 𝜌= 𝑉
● The density ρ is in kilograms per metre cubed, kg/m 3, the mass m is in kilograms, kg, and
the volume V is in metres cubed, m 3.
Effects of forces
● Newton’s first law states that an object has a constant velocity unless acted on by a
resultant force.
● Newton’s second law states that 𝒇𝒐𝒓𝒄𝒆 = 𝒎𝒂𝒔𝒔 × 𝒂𝒄𝒄𝒆𝒍𝒆𝒓𝒂𝒕𝒊𝒐𝒏 𝑭 = 𝒎𝒂
● Newton’s third law states that every action force has an equal and opposite reaction force.
For example, the force of the Earth’s gravity on an object is equal and opposite to the force
of the object’s gravity on the Earth.
Friction is a force between two surfaces which impedes motion and results in heating. Air
resistance is a form of friction.
To find the resultant of two or more forces acting along the same line, they should be added
together if in the same direction and subtracted if in the opposite direction.
● Elastic deformation:
○ The object returns to its original shape when the load has been removed, an
example being a spring being stretched under normal usage.
● Plastic deformation:
○ The object does not return to its original shape when the load has been removed,
an example being a spring that has been stretched too far.
Hooke’s law states that for a spring, 𝐹 = 𝑘𝑥 where F is the force applied to the spring in 𝑁, k
is the spring constant in 𝑁𝑚−1 , and x is the extension in 𝑚.
Turning effect
The moment of a force is a measure of its turning effect: 𝑚𝑜𝑚𝑒𝑛𝑡 𝑜𝑓 𝑎 𝑓𝑜𝑟𝑐𝑒 = 𝑓𝑜𝑟𝑐𝑒 ×
𝑝𝑒𝑟𝑝𝑒𝑛𝑑𝑖𝑐𝑢𝑙𝑎𝑟 𝑑𝑖𝑠𝑡𝑎𝑛𝑐𝑒 𝑚𝑜𝑚𝑒𝑛𝑡 = 𝐹𝑑
For example, when riding a bike, pressing your foot down on the pedal causes a moment about the
pivot, turning the pedal arms.
● The pivot point is the point which the object can rotate about.
● If a force is applied in the same line as the pivot (see first example in diagram) the object
will not rotate, and will remain stationary.
● If the force applied is in a different line to the pivot, it will rotate in the direction of the force.
○ If it is perpendicular to the object, then the perpendicular distance is the length of
the object (see second example in diagram).
○ If it is not perpendicular to the object, then the perpendicular distance to the pivot
must be found (see third example in diagram).
The principle of moments can be applied to check whether something balances. An experiment
can be performed to show that there is no net moment on a body in equilibrium by pivoting
a uniform ruler at its centre and placing different masses at different distances from the
centre on either side until it balances, and showing that the clockwise and anticlockwise
moments are equal.
Centre of Mass
The centre of mass of a body is the point at which all of its mass can be considered to act. To
calculate the centre of mass of a card:
1. Hang up the card and suspend a plumb line from the same place.
2. Mark the position of the thread.
3. Repeat the above steps with the card suspended from different places.
4. Where these lines intersect is the centre of mass.
If the centre of mass is below the point of suspension of an object, it will be in stable equilibrium
(e.g. a hanging plant pot). If the centre of mass is above the point of suspension of an object, it will
be in unstable equilibrium (e.g. a pencil placed on its sharp end). If the line of action of the object’s
weight moves outside the base, there will be a resultant moment and it will topple.
Examples:
Scalars Vectors
Distance Displacement
Speed Velocity
Time Acceleration
In elastic collisions, the total kinetic energy before is equal to the total kinetic energy after.
Example:
● A 10kg stationary gun is loaded with a 10g bullet. It is fired, with the bullet travelling
at 𝟏𝟎𝟎𝒎𝒔−𝟏 . What is the recoil speed of the gun?
𝟎 = 𝟎. 𝟎𝟏 × 𝟏𝟎𝟎 + 𝟏𝟎𝒗
𝒗 = −𝟎. 𝟏𝒎𝒔−𝟏
So the recoil speed is 𝟎. 𝟏𝒎𝒔−𝟏 (-0.1ms-1 is the velocity which is a vector, so we take the
magnitude of it as we are finding the speed).
Energy transfers
Energy can be transferred between different forms including kinetic, gravitational potential,
chemical, elastic potential, nuclear and internal energy as a result of an event or process.
𝟏
● Kinetic energy: 𝑬𝒌 = 𝒎𝒗𝟐
𝟐
● Gravitational potential energy: 𝐸𝑝 = 𝑚𝑔ℎ
Work is done when a force moves something through a distance. The work done is equal to the
energy transferred.
● Work done: 𝒘𝒐𝒓𝒌 𝒅𝒐𝒏𝒆 = 𝒇𝒐𝒓𝒄𝒆 × 𝒅𝒊𝒔𝒕𝒂𝒏𝒄𝒆 𝑾 = 𝑭𝒅
Power is the rate at which energy is transferred or the rate at which work is done. For example, a
lamp with a greater power will be brighter because it transfers more energy from electrical energy
to light and heat energy in a given time.
𝑒𝑛𝑒𝑟𝑔𝑦 𝑡𝑟𝑎𝑛𝑠𝑓𝑒𝑟𝑟𝑒𝑑 𝐸
● Power: 𝑝𝑜𝑤𝑒𝑟 = 𝑃=
𝑡𝑖𝑚𝑒 𝑡
Energy is always conserved. The total energy before is equal to the total energy after.
For example, when a ball is dropped, gravitational potential energy becomes kinetic energy
as it accelerates downwards. Upon impact with the floor, this kinetic energy will become
thermal energy and sound energy.
In any event or process energy tends to become more spread out among the objects and
surroundings (dissipated).
● The efficiency is the ratio of the useful work done to the total energy supplied, often
expressed as a percentage.
𝒖𝒔𝒆𝒇𝒖𝒍 𝒆𝒏𝒆𝒓𝒈𝒚 𝒐𝒖𝒕𝒑𝒖𝒕 𝒖𝒔𝒆𝒇𝒖𝒍 𝒑𝒐𝒘𝒆𝒓 𝒐𝒖𝒕𝒑𝒖𝒕
○ Efficiency: 𝒆𝒇𝒇𝒊𝒄𝒊𝒆𝒏𝒄𝒚 = 𝒕𝒐𝒕𝒂𝒍 𝒆𝒏𝒆𝒓𝒈𝒚 𝒊𝒏𝒑𝒖𝒕 = 𝒕𝒐𝒕𝒂𝒍 𝒑𝒐𝒘𝒆𝒓 𝒊𝒏𝒑𝒖𝒕
Energy sources
It is important to note that apart from geothermal, nuclear and tidal, the sun is the original
source of all energy on earth, released by nuclear fusion.
● Renewable energy is energy which can be replenished as quickly as it is used. Examples
include:
○ Biofuel
○ Wind
○ Hydro-electricity
○ Geothermal
○ Tidal
○ Solar
○ Water waves
It is often more costly and less reliable than non-renewable energy (e.g. the wind is
intermittent and solar energy relies on good weather).
● Non-renewable energy is used more for large-scale energy supplies due to the large
energy output per kilogram of fuel. Examples include:
○ Fossil fuels (coal, oil, gas)
○ Nuclear fuel
It is usually cheaper than renewable energy but is becoming less popular because one day
it will run out and it is harmful for the environment (e.g. burning fossil fuels releases
greenhouse gases which cause global warming).
Pressure
Pressure in fluids causes a net force at right angles to any surface and is measured in Pascals.
𝑓𝑜𝑟𝑐𝑒 𝐹
𝑝𝑟𝑒𝑠𝑠𝑢𝑟𝑒 = 𝑝=
𝑎𝑟𝑒𝑎 𝐴
Measuring pressure:
● A barometer consists of a tube filled with mercury with a vacuum at
the top. Atmospheric pressure pushes down at the sides causing
the mercury to rise. The height of the mercury is measured to find
atmospheric pressure, where 760 mm or 29.92 in of mercury
corresponds to 1 atm.
● A manometer consists of a U-tube filled with mercury and with a
gas at either end. The difference in the height of the mercury on
either side can be measured to find the pressure difference
between the two ends of the tube.
The pressure beneath a liquid surface increases with depth and density.
● It is given by 𝒑 = 𝝆𝒈𝒉