dynamics

• distance, d


  - how far an object has travelled

  - measured in metres, m
• speed, v


  - distance travelled per unit of time

  - measured in metres per second, ms-1
• displacement, s


  - shortest distance between start and finish, including direction

  - measured in metres, m
• velocity, v


  - displacement per unit of time, including direction

  - measured in metres per second, ms^-1
• acceleration, a


  - change in speed/velocity per unit of time

  - measured in metres per second per second, ms^-2
• scalar quantities


  only have magnitude (size)
• vector quantities


  have both magnitude (size) and direction
• scalar quantity examples


  - time

  - distance

  - speed

  - mass

  - energy

  - power

  - temperature
• vector quantity examples


  - force

  - velocity

  - displacement

  - acceleration

  - weight
• how to add forces when they're acting in the same direction

  add them together
• how to add forces when they're acting in opposite directions

  subtract the smaller from the larger
• force, F


  - a push or a pull, or a combination of both (twist or tear)

  - measured in newtons, N
• what changes can a force make on an object?

  - its shape

  - its speed

  - the direction it is travelling in
• thrust, Th


  force from an engine or rocket
• weight, w

  - downward force due to gravity (W=mg)

  - force that is exerted on all objects with mass that have gravity acting on them (what keeps masses on the ground)

  - measured in newtons, N, using a newton balance

  - variable (depends on how strong the force of gravity is)
• friction, Fr


  force opposing motion
• tension, T


  pulling force of string, rope, cable or chain
• buoyancy force, B or U


  upward force due to floatation
• lift, L


  upward force generated by wings or rotors
• reaction, R


  force of contact from a surface (always at right angles to the surface)
• mass, m


  - the quantity of matter which makes up an object

  - measured in kilograms, kg, using a balance

  - only changes when particles are added or removed
• gravitational field strength, g


  - weight per unit mass

  - measured in newtons per kilogram, Nkg-1
• gravitational field strength on Earth


  9.8 N/kg^-1
• what is the relationship between weight and mass?

  directly proportional
• balanced forces


  - equal in size

  - opposite in direction

  - result in an object remaining stationary or moving at a constant speed
• unbalanced forces


  - more force acts in one direction than in the opposite direction

  - results in an object accelerating or decelerating
• newton's first law of motion

  "an object will remain at rest or continue to move at constant speed in the same direction unless acted upon by an unbalanced force"
• newton's third law of motion

  if object A exerts a force on object B, object B exerts an equal and opposite force on object A
• freefall


  - when an object is being accelerated towards the centre of the Earth (or other body) due to gravitational field strength

  - when an object is in freefall it also appears to be weightless
• terminal velocity


  when an object reaches a velocity where the frictional force is equal to the force causing the motion (e.g. thrust from an engine, or weight of a falling object) the forces are now balanced and the object will no longer accelerate
• kinetic energy, Ek


  - all moving objects have kinetic energy

  - the value of Ek depends on the object's mass and its speed/velocity
• gravitational potential energy, Ep


  - the energy gained by an object which is lifted in a gravitational field

  - depends on the object's mass, the gravitational field strength and the height the object is lifted to
• work done, Ew


  - work is done when energy is transferred

  - sometimes represented by W

  - depends on the force applied to the object and the distance travelled by the object
• power, P


  - the work done per unit of time

  - measured in watts, W
• why does a projectile follow a curved path?

  has a ~

  - constant horizontal velocity

  (this is because no forces act horizontally on the object once it is in flight)

  - constant vertical acceleration (of 9.8 ms-2 on Earth)

  (this is because the only force acting vertically on the object its weight once it is in flight)

  both these motions must be considered separately
• how to calculate distance travelled from a v-t graph

  aug