topic 9 - forces and their effects

Cards (41)

  • scalar quantities : only have magnitude
    vector quantities : have both magnitude and direction
  • examples of scalar quantities
    • distance
    • mass
    • temperature
    • density
    • energy
    • speed
    • time
  • example of vector quantities
    • weight
    • velocity
    • acceleration
    • force
    • displacement
  • Efficiency
    • efficiency = useful energy / total energy
    • efficiency= useful power / total power
  • Friction is a force that is always against a motion between surfaces.
  • Drag is a force that is always against a motion through a fluid.
  • Thrust is a forward force or movement given to an object due to the expulsion of an object.
  • Tension is a force through a material opposing an action force.
  • Upthrust is a force acting up due to the displacement of a fluid.
  • Electromagnetic force is an attraction or repulsion depending on the charge or poles.
  • Gravitational force, also known as weight, is a force exerted on another object due to a massive object.
  • Normal contact force is a reaction force or force that opposes a force applied on a surface.
  • Spring force is a force acting on a spring either to expand or compress.
  • lubricants
    • reduces amount of friction ( wasteful energy )
    • reduces amount of work done against friction
  • force : is a push or pull that acts on an object , causing a change in motion onto an object ( acceleration )
  • resultant : the sum of all vectors of the same type , resulting in a single vector acting on an object
    resultant force : sum of all individual forces acting on an object , resulting in a single force causing acceleration
  • objects affecting each other
    • objects interact by exerting forces on eachother ,
    • these two forces ( earth and moon example ) are action reaction forces ( newton's third law pair ) . these forces are the same size , opposite direction and acting on different objects
    • no actual contact between moon and earth - fields ( electric and gravitational )
    • these are non contact forces
  • types of forces
    1. contact forces
    • tension
    • friction
    • upthrust
  • types of forces
    1. contact forces
    • tension
    • friction
    • upthrust
    2. non contact forces
    • gravity
    • static electricity - magnetism
  • examples of contact forces
    • upthrust/lift - act upwards in air
    • friction (on land ) / air resistance (in air ) / drag ( in water ) - act against the direction of movement
    • push/pull - forces that also act in the direction of movement , generated by direct contact between objects ( not by engine power )
  • examples of non contact force
    • weight ( gravity ) - acts between objects with mass
    • magnetic force - magnets can attract objects from magnetic materials , can attract or repel objects , do not have to physically touch to affect each other
    • electric field - object charged with static electricity , has electric fields around it , can affect objects
  • contact forces - between two objects touching eachother
  • non-contact force = occurs between two objects due to a field : without touching
  • field : a region of space in which a object will experience a force based on one of its properties
  • types of fields - magnetic fields
    • magnetic force
    • non-contact
    • can be attractive or repulsive
  • types of fields - electrical fields
    • electrostatic force
    • non - contact
    • can be attractive / repulsive
  • types of field - gravitational field
    • gravitational force ( weight )
    • non - contact force
    • always attractive
  • free body diagrams
    1. forces originate from a body
    2. forces are acting from a single object
    3. forces must be labeled
    4. arrows must be proportional to size of force
  • weight must always act downwards , towards the centre of a massive object
  • the normal contact force must be perpendicular to the surface
  • vectors :
    • vectors which are perpendicular to each other are independent of one another - cannot be added or taken away
    • conventionally up is positive and towards the right is positive
  • vector diagrams
    • resulting ( vectors ) : representing a single force as two-forces drawing the horizontal and vertical component
  • reducing friction
    • using a lubricant : devices waste a lot f energy for various reasons due to friction between moving parts
    • energy is wasted in the form of : thermal and sound
  • thermal energy : the part around , where energy is wasted due to friction, will increase in temperature as they gain thermal energy
  • benefits of reducing friction :
    • it is the amount of friction is reduced , less energy is wasted
    • the efficiency of the device increases
  • using lubricants
    • a method of reducing the amount of energy wasted , due to friction is by using a lubricant
    • lubricant reduces the friction experienced around a turning point of a device by allowing the surface to slide smoothly over eachother
    • examples : door hinge , car engine ( moving pistons ) , gears
  • moments
    • a moment is the turning effect of a force around a fixed point ( called a pivot )
    • the size of a moment depends on two factors
    • size of the force applied
    • perpendicular distance from the pivot to the line of action of the force
  • moment of a force ( Nm / newton metres ) = Force ( N ) x distance perpendicular to direction of force ( m )
  • principle of moments
    sum of clockwise moments = sum of anti-clockwise moments
    when in equilbrium
  • leavers
    • leavers are used to transfer force
    • reduce force required to perform an action
    A) effort distance
    B) effort
    C) load distance
    D) load