forces

• difference in scalars and vectors

  SCALAR : only have magnitude ( size ) , but no direction.

  • E.G speed , distance , mass , temperature and time , energy

  VECTORS: have both magnitude and direction

  • E.G velocity , displacement , acceleration , force and weight.
• forces :

  • forces acting in the same direction can be added together
  • forces acting in opposite directions can be subtracted
• resultant forces :

  • can be resolved into their horizontal and vertical components.
  • length = magnitude
  • way its pointing = direction
• newton's first law :

  • a resultant force is required to change the motion of an object
  • if there isn't a resultant force = objects motion wont change
  • if an object is stationary and its resultant force is 0 = remain stationary
  • if an object is moving and its resultant force is 0 = carry on moving at the same velocity
• newton's third law :

  when two objects interact the forces they exert on each other are equal and opposite

  equal = magnitude of the two forces

  opposite = direction of the two forces
• define acceleration :

  the rate of change in velocity - how quickly something speeds up or slows down.
• acceleration equations :

  a = acceleration , v = final velocity , u = initial velocity , t = time

  
• acceleration equation (2) :

  a = acceleration (m/s2) , s = distance (m) , v = final velocity ( m/s ) , u = initial velocity ( m/s )

  
• define deceleration :

  negative acceleration ( slowing down )
• velocity time graphs ( 2 ) :

  finding the distance travelled :

  • calculating the area under the curve.
  • remember you can split the area into shapes then add the total.

  finding it under curved areas :

  • count number of squares under the section of the graph.
  • partially full squares try to combine them.
• newtons 2nd law :

  (1) - if a non zero resultant force acts on an object, then it will cause the object to accelerate.

  (2) - acceleration of an object is proportional to the resultant force acting on it and inversely proportional to its mass

  EQUATION : F = MA , f = resultant force , m = mass , a = acceleration

  EXAMPLE : CIRCULAR MOTION

  • speed remains constant however direction is always changing.
• define inertial mass :

  how difficult it is to change an object's velocity.

  • define as the ratio of force over acceleration
• define stopping distance :

  minimum distance required to stop a vehicle in an emergency

  • EQUATION : total of stopping distance = thinking distance + braking distance
• define thinking distance

  how far the car travels during the driver's reaction time - time between the drive seeing the hazard and then applying the brakes.

  THINGS THAT AFFECT THINKING DISTANCE :

  • speed of the vehicle ( faster = further you'll travel )
  • reaction time ( vary between people = e.g tiredness , drunk , drugs or being distraction = increases reaction time )
• define braking distance :

  • distance taken to stop under the braking force .

  FACTORS :

  • road conditions ( wet / icy = less friction between tires and road = car to skid )
  • condition / quality of brakes ( worn of fault = wont slow down quickly = travel further before it stops )
  • speed of the vehicle
  • mass of the vehicle
  • both increase kinetic energy of the vehicle ( which has to reduced back to 0 in order for the vehicle to stop )
• define work done :

  when a force causes an object to move through a distance work is done on the object = a force does work on an object when the force causes a displacement of the object

  • work done against the frictional forces acting on an object causes a rise in temperature of an object

  EQUATION : w = fs , w = work done , f = force , s = distance moved along the line of the action of the force
• deformation :

  elastic - return to its original shape after forces have been removed

  inelastic - cannot return to its original shape - stays deformed after forces have been removed
• 1.4 extension& hookes law

  increase in length of a spring when it's stretched

  
  

  hookes law : the extension of an elastic object is directly proportional to the force applied, within the extension

  
  

  EQUATION : F = ke , f = force (n) , k =spring constant of an elastic object( n/m ) , e = extension (m)
• 1.1 contact& non contact forces

  what is force ?

  a push or pull , that acts on an object due to its interaction with another object - measure forces in N

  forces have direction and magnitude = vector quantities .
• 1.1 contact&non contact forces

  contact forces examples : objects are physically touching

  • friction
  • air resistance - collision between object + air particles
  • tensions
  • normal contact force ( reaction force ) - equal and opposite force

  non contact forces examples : don't require objects to be touching

  • gravitational force
  • magnetic force - can be attractive or repulsive
  • electrostatic force - between charged objects - can be attractive or repulsive

  -- > they can act on anything --> decrease as the objects get further apart
• 1.3 speed&velocity + distance&displacement

  scalar quantities : only have magnitude e.g SPEED + DISTANCE

  vector quantities : have both magnitude + direction e.g VELOCITY

  + DISPLACEMENT

  equations :

  speed = distance / time ( m / s ) -

  velocity = displacement / time ( m / s + the direction e.g m / s east )

  negative velocity = going backwards

  1 - s = d / t

  2 - v = s / t/
• 1.2 free body diagram&resultant force

  free body diagrams show all the forces acting on an object .

  example :

  arrows = force arrows

  all forces here are vectors as they have magnitude and direction.

  since they all act in different directions = cancel each other out = whatever is left is the resultant force ( the overall force on an object )

  
• 1.3 resolving forces into components

  aim : split it up into its vertical and horizontal components by using a scale drawing.
• 1.4 changing shape of an object .

  by applying force on a object you can either :

  • compress
  • stretch
  • bend
• 1.4 force + extension graph

  A - elastic deformation

  B - the elastic limit / limit of proportionality

  C - Inelastic deformation

  
• 1.4 spring constant :

  definition : an object's spring constant is a measure of how many newtons of force it would require to stretch ( or compress ) the object by 1 metre . -- units = n / m

  • you can think of it as a measure of how stiff the object is - objects with a high spring constant are more stiff so they require more force to stretch .

  lower spring constant = object more elastic + less firm

  higher spring constant = object is less elastic + more firm
• 1.4 equations of elasticity ( 2 )

  e = 1/2 x k x e (squared)

  e =elastic potential energy ( J ) , k = spring constant ( n / m ) , e = extension ( m ) ( squared )

  elastic potential energy = energy transferred to an object as its stretched
• 1.5 Velocity time graphs :

  gradient = change in velocity / change in time

  • the gradient tells you the acceleration e.g constant positive gradient = constant positive acceleration
  • flat sections = velocity is constant as it’s not increasing nor decreasing
  • Curve gets steeper = gradient + acceleration is increasing

  
• 1.6 momentum + conservation .

  momentum is a property that all objects have. - vector quantity = has both direction + magnitude .

  equation :

  momentum = mass x velocity
• 1.6 momentum + conservation of momentum .

  the conservation of momentum principle :

  the idea that in a closed system , the total momentum before the event ( e.g a collision ) is the same as the total momentum after the event.

  to find the total momentum before = add the momentum of two objects .

  calculate their shared velocity equation :

  velocity = momentum / mass