Yr 10 Physics March 2017

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

• Motion Equations you need to be familiar with:

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

• acceleration = change in velocity / time taken  

•  SUVAT EQUATIONS:   s = ½ (u + v) t,    a  =  (v - u) / t ,    v2 = u2 + 2 a s

• 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 vectors to be combined are at right angles then

  the resultant is reprented by the diagonal of the rectangle  as shown below:

• eg. the resultant can be found by drawing the rectangle above to scale using say, 1cm = 1N,
   then measure the length of the diagonal and convert it to N.

• 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.

• Electric fields exist around charged objects (like magnetic fields around magnets)

 • Electric field direction is always + to –  

 • Electric field is strongest where field lines are closest together


• 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 insecticide sprayers.

• Electrostatic charge build up can be a nuisance, eg. lightning.


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.