Yr 10 Physics iGCSE: Revision Notes 2

Formulae you need to know are in bold.



1 Motion Graphs

• The slope or gradient of a distance-time graph represents speed.

• The velocity of a body is its speed in a given direction, velocity is a vector.

  NB other examples of vectors are force, acceleration, momentum.

• quantities with no specified direction are called scalars

  NB examples of scalars are energy, time, distance, temperature, etc

• average velocity = total distance / total time,   v  =  d/t

• acceleration = change in velocity / time taken,    a  =  v - u / t  

• The slope(gradient) of a velocity-time graph = acceleration.

• The area under a velocity-time graph = distance travelled.


2 Forces

• Force is a vector (like velocity, it has size and direction)

• Distance or speed are called  scalars, they have size but not direction.

• The faster a body moves through a fluid the greater

the opposing frictional force which acts on it.

• A body falling through a fluid will initially accelerate

due to gravity, eventually the resultant force on the body

will be zero, and it will fall at its terminal velocity.

• at terminal velocity Weight down = Friction up

• weight = mass Χ gravitational field strength,  W  = mg

(newton, N) (kilogram, kg) (newton/kilogram, N/kg)

• Whenever two bodies interact, the forces they exert

on each other are equal & opposite (Newton's Third Law)

• A number of forces acting on a body may be replaced by

a single force which has the same effect as the original set

of forces. The single force is called the resultant force (here in red):

• If the resultant force acting on a stationary body is zero,

it is either at rest, or moving at a steady speed.

• If the resultant force acting on a stationary body is not zero,

the body will accelerate in the direction of the resultant force.

• Resultant force = mass Χ acceleration,   OR,   F = ma

(newton, N) (kilogram, kg) (metre per second squared m / s2 )

• When a vehicle travels at a steady speed the frictional

forces balance the driving force (zero resultant force).

• Stopping distance = braking distance + thinking distance.

Typical Stopping Distances


The Highway Code by Select All

The Highway Code by Select All


9 metres     14 metres

= 23 metres
(75 feet)
or 6 car lengths


The Highway Code by Select All

The Highway Code by Select All


15 metres

38 metres

= 53 metres
(175 feet)
or 13 car lengths


The Highway Code by Select All

The Highway Code by Select All

The Highway Code by Select All


21 metres

75 metres

= 96 metres
(315 feet)
or 24 car lengths

 The Highway Code by Select AllThinking Distance

 The Highway Code by Select AllBraking Distance

 http://www.highway-code.com/images/wt.gifhttp://www.highway-code.com/images/wt.gifaverage car length = 4 metres

• A driver’s reaction time is affected by tiredness, age, drugs, or alcohol.

• A vehicle’s braking distance depends on the brakes, tyres, the road, and weather.


3 Work, Energy, Power

• When a force causes a body to move through a distance,

 energy is transferred, and work is done.

• work done = force Χ distance moved in direction of force,   W  =  F x d

     (joule, J) (newton, N) (metre, m)

• Work done against frictional forces is mainly changed into heat.

• Squashed materials have elastic potential energy stored in them.

• The kinetic energy of a body depends on its mass and its speed.

      kinetic energy = ½  x  mass  x  v2 ,     KE =   ½  m v2

(joule, J) (kilogram, kg) (metre/second)2 , (m/s)2 )

• Gravitational Potential Energy GPE depends on height and weight:

    GPE  =  weight  x  height  ,   GPE  =  m g h

   (Joule J,  Newtons N,  metres m)

•  Power  =  work done /  time taken,   P  =  W / t

     P = Work / t   or  Energy / t ,  units are Watts


4 Momentum

• momentum = mass Χ velocity ,   mom. = mv

(kilogram metre/second, kg m/s) (kilogram, kg) ( m/s)

• Momentum has both size and direction (another vector)

• When a force acts on a body a change in momentum occurs.

• Momentum is conserved in any collision/explosion,

provided no external forces act,

ie. momentum before collision = momentum after collision

 Top - two trolleys of same masses exploding apart, bottom - two trolleys of different masses exploding apart

• force = change in momentum / time taken for change,   F  =  mv - mu / t

we use this equation to explain why the force is large when the impact time is small

in a collision.


5 Static electricity

• When materials are rubbed against each other they can

become electrically charged. Negatively charged electrons

are rubbed off one material onto the other.

• The material that gains electrons becomes negatively charged.

The material that loses electrons has an equal positive charge.

• Two charged bodies will exert a force on each other.

• Like charges repel, unlike charges attract.

• Electric charges move easily through metals (conductors), but not through insulators.

• The rate of flow of electric charge is called the current.

• current in a wire is a flow of negatively charged electrons

   current  =  charge / time,  OR,   Q  =  I t

     (Amps)       (Coulombs)   (seconds)

• A charged body can be discharged by connecting it to earth

with a conductor. Charge then flows through the conductor.

The greater the charge on an isolated body the greater the potential

difference between the body and earth. If the pd is high enough a

spark may jump to earth.

• Electrostatic charges can be useful, eg in photocopiers and ink jet printers.


6 Electric Current

• Current-potential difference graphs are used to show how

current through a component varies with pd across it.

A resistor               A filament lamp                  A diode

• The current through a resistor (at a constant temperature)

is proportional to the voltage across the resistor.

• Voltage = current Χ resistance,   V  =  I R

     (volt, V) (ampere, A) (ohm, Ω)

• The resistance of a filament lamp increases as the

 temperature of the filament increases.

• The current through a diode flows in one direction only.

The diode has a very high resistance in the reverse direction.

• The resistance of a light-dependent resistor (LDR)

 decreases as light intensity increases.

• The resistance of a thermistor decreases as the temperature increases.

• The current through a component depends on its resistance,

 the greater the resistance the smaller the current.

• The voltage from cells in series is the sum of the voltage of each cell.

• Rules for components connected in series like below:





− total resistance = sum of the resistance of each component

− there is the same current through each component

− the total voltage of the supply is shared between the components.

• Rules for components connected in parallel:

− voltage across each component is the same

− the total current through the whole circuit is the sum

 of the currents through the separate components.

•  in series circuits if 1 item fails, all items turn off, in parallel circuits

  other items still work, ALSO all items can be switched independently so

  parallel wiring for lighting is preferred.


7 Mains electricity

• Cells and batteries supply current which always passes in

 the same direction. This is called direct current (d.c.).

• An alternating current (a.c.) is one which is constantly

changing direction. Mains electricity is an a.c. supply.

In the UK it has a frequency of 50 cycles per second (50 Hz).

• UK mains supply is about 230 volts.

• Know the structure and wiring colours of a three-pin plug.

• If an electrical fault causes too great a current, the circuit

 should be switched off by a fuse or a circuit breaker.

• When the current in a fuse wire exceeds its rating the

 fuse will melt, breaking the circuit.

• in a circuit breaker a magnetic force acts to break the circuit (this

  has the advantage of a quick re-set)

• Appliances with metal cases are usually earthed. The earth

wire and fuse together protect the appliance and the user

• Plastic cased appliances need no earth (they are said to be double insulated)

• The live terminal of the mains supply alternates between

positive and negative potential with respect to the neutral terminal.

• The neutral terminal stays at a potential close to zero

 with respect to earth.


8 Electrical Power

• Electric current is the rate of flow of charge.

• When an electrical charge flows through a resistor,

 electrical energy is transformed into heat energy.

• power = energy transformed / time taken,   P =  E / t

• Power, voltage and current are related by the equation:

power = voltage x current,   P  =  VI

(watt, W) (ampere, A) (volt, V)

Energy = power x time, so:

energy = voltage x current x time,   E  =  VIt  = VQ.

• Voltage is the energy transferred per Coulomb of charge flowing

  1 VOLT  =  1 JOULE /  1 COULOMB 


9 Atomic structure by Rutherford Scattering

Remember the structure of an atom from Year 9 -   Rutherford, an English physicist is credited

with doing the experimental work which established the so called 'nuclear model' :

In RUTHERFORD SCATTERING alpha particles are fired at a thin gold foil.

● Most alphas go straight through unaffected.

● A small number are reflected through large angles

● A tiny number bounce directly backwards.

From these observations we deduce:

● an atom is mostly empty space

● all of the positive charge and most of the mass is concentrated in a

    tiny dense nucleus

● negatively charged electrons are in orbits around the nucleus

10 Nuclear fission

• There are two fissionable substances in common use

 in nuclear reactors, uranium 235 and plutonium 239.

• Nuclear fission is the splitting of an atomic nucleus.

• For fission to occur the uranium 235 or plutonium 239 (blue in the diagram below)

 nucleus must first absorb a neutron (red in the diagram):

• The nucleus undergoing fission splits into two smaller

 nuclei (yellow in the diagram) and 2 or 3 neutrons and energy is released.

• The neutrons may go on to start a chain reaction, AS ABOVE.

• In a nuclear reactor (below), the uranium or plutonium is contained in fuel rods. Fissions occur

   inside these rods producing fast neutrons and causing heating.,

• the moderator (usually water) is used to slow down the fast neutrons to increase the chances

of further fissions occurring (to promote a chain reaction)

• the control rods (usually boron) are lowered  to absorb neutrons to reduce the reaction

  or to shut down the reactor. 

•  The fission fragments (the leftovers after a fission reaction) are highly radioactive with long half lives,

   this is the radioactive waste from a reactor and disposal is a problem.



•  Density of an object = its mass divided by its volume,     

 Density  =  mass  /  volume                                              ρ  =  m  / V                                      

      (kg/m3)      (kg)         (m3)

• You should be able to describe an experiment to measure the density of an object

  involving measurements of its mass, and its volume.