5-Forces

• forces

  • a force is a push or pull that acts on an object due to it's interaction with another objects
  • forces can be contact or non-contact
  • force is measured in newtons (N)
  • forces are vectors because they have both magnitude and direction
• magnitude and direction

  • magnitude is size
  • direction is the course in which the object moves
• contact forces

  • require objects to physically touch
  • they include friction, air resistance, tension, normal contact force (reaction force)
• non-contact forces

  • don't require objects to physically touch
  • they include gravitational, magnetic, electrostatic forces
  • they can act through empty space
  • their strength decreases as objects get further apart
  • they are 'fields of influence' around an object - the forces can act on anything surrounding that area
• forces

  • friction - when two objects slide past each other
  • air resistance - when an object moves through the air
  • tension - when an object is being stretched
  • reaction - when an object is at rest on a surface
  • gravitational - when any mass is in a gravitational field
  • magnetic - when an object is magnetic in a magnetic field
  • electrostatic - when a particle is charged in an electric field
• scalars and vectors

  • scalars only have a magnitude and no direction
  • some examples of scalars - speed, distance, time, mass, temperature, power
  • vectors have both a magnitude and a direction
  • some examples of vectors - velocity, displacement, acceleration, force, momentum
• free body diagrams

  • they show all the forces acting on an object with force arrows to figure out the resultant force
  • when all forces balance out the object is in equilibrium
  • magnitude - the length of the arrows
  • direction - the direction of the arrow
• scale drawings

  • draw force lines tip to tail
  • draw a line from starting to end point - measure with ruler to find resultant force
  • direction - measure angle with protractor - bearings are from north clockwise

  
• • when applying force to an object you can force it to stretch, bend or compress
  • this requires the minimum of 2 forces
• deformation

  • deformation is the change in shape of an object in result of forces being applied to it
  • two types - elastic and inelastic
  • elastic - when an object returns back to it's original shape after forces have been removed
  • inelastic - when an object doesn't return back to it's original shape
• extension

  • extension is the increase in length of a spring when it is stretched
  • when adding a mass to a spring that increases it's length so we can measure it's extension - F proportional to e
  • solid support is exerting an equal but opposite force to hold it up

  
• spring constant

  • force = spring constant x extension
  • F = k x e
  • units:
  • force - newtons(N)
  • spring constant - N/m
  • extension- metres (m)
  • the higher the constant, the stiffer the material as it takes more force to stretch it
• force-extension graphs

  1. as force increases extension increases - directly proportional - elastic deformation - Hooke's law
  2. line starts to curve - elastic limit - limit of proportionality - Hooke's law doesn't apply
  3. then the line curves more - inelastic deformation
• elastic potential energy

  • elastic potential energy = 1/2 x spring constant x extension squared
  • Ee = 1/2 x k x e squared
  • units:
  • elastic potential energy - joules (J)
  • elastic potential energy is the energy transferred to an object when it's being stretched
• force-extension graphs

  • elastic potential energy is area under the curve

  A) elastic potential

  B) spring constant

  
• speed

  • speed = distance divided by time
  • s = d/t
  • units:
  • speed - m/s
  • distance - m
  • time - s
• velocity

  • velocity = distance divided by time
  • v = s/t
  • units:
  • velocity - m/s
  • distance - m
  • time - s
  • it is a vector
• acceleration

  • time taken to gain speed/ change in velocity
  • acceleration = change in velocity divided by time
  • units:
  • acceleration - metres per second squared (m/s squared)
  • change in velocity - m/s
  • time - seconds
• s is the symbol for distance
• acceleration

  • 2 x acceleration x distance = final velocity squared -initial velocity squared
  • 2as = v squared x u squared
• gradient-time graph

  • gradient = speed
• velocity-time graphs

  • area under the graph is the distance - area of triangle = 1/2bh, or count the squares - m
  • straight line - constant velocity
  • increasing/decreasing line - de/acceleration
• terminal velocity is when velocity remains constant