newtons laws, work done

• Work done equation


  Workdone (Nm or J) = Force (N) X distance (m)

  
• Kinetic energy equation


  Kinetic energy (J) = 1/2m(v squared)

  
  

  m= mass (kg)

  v= velocity (m/s)

  
• Gravitational potential energy equation

  GPe (J) = mass (kg) X gravity (m/s squared) X height (m)

  
• Weight equation


  w (N) = m (kg) X g (m/s squared)

  
• Work done is equivalent to

  Energy transferred
• Force equation (extension)


  F=Kx F= force (N) K = spring constant (N/m) x= extension (m)

  
• Hooke's law


  W=1/2Fx F=force (N) x=extension (m) W= work done (Nm or J)
• Work done in stretching a spring is determined by

  Finding the area under the curve and can be found with W=1/2Fx
• Total energy is


  All the energies added up
• Some energy is always lost as

  Heat or sound

  when energy is transformed from one form to another
• To work out frictional force (energy lost whilst doing action)

  Energy lost = total energy at start -total energy at end

  
  

  Energy lost/height or distance
• Mean resistive force


  1. W= Fd

  2. W= energy transferred

  (Usually GPe - Ke) (sometimes energy transferred to surroundings)

  3. Rearrange F=W/d
• Kinectic energy at most when?

  When at lowest point , no GPe.
• GPe most when?


  When stationary, no Ke.
• When object moves through the air...

  The Total energy will distribute between kinetic and GPe but total will always stay the same.
• At any point total energy is equal to...


  The sum of Ke and GPe
• Newton's First Law


  An object remains at rest or constant speed unless acted upon by external force.

  
• Newton's Second Law


  Resultant force (N) = mass (kg) X acceleration (m/s squared)

  
• Newton's Third Law


  In an interaction between 2 objects, if object A exerts a force on object B then object B will exert and EQUAL AND OPPOSITE FORCE on object A.

  
• 1st condition Newton's 3rd Law

  1. 2 forces of equal size act in opposite directions
• 2nd condition Newton's 3rd Law

  2. 2 forces in interaction pair act on different objects.
• 3rd condition Newton's 3rd Law

  3. 2 forces are always the same type e.g they will both be a gravitational force
• Action force?


  Force acts in one direction on object.

  
• Reaction force?


  Force exerted on object opposite to action force.

  
• Interaction pair?


  Action-reaction force pair.

  
• Contact force?


  Force exerted on object due to contact with object.

  
• Action at a distance force?


  Force that act on objects without touching them such as gravity.

  
• A force can either be a


  Contact force or action at distance force.
• Example of Newton's 3rd Law

  Rugby scrum :

  Player exerts backwards force on ground. Ground exerts equal and opposite force.
• Airbags?


  Increases time it takes for head to come to rest. Reducing force impact.

  
• Seat-belts?


  Increases time it takes for body to come to rest. Reduces force impact.

  
• Need new seat-belts after crash?

  Yes
• Crumple zones?


  Front part of car absorbs more energy meaning less energy absorbed by person.

  
• Modifications to make car better?

  Move height: closer to wheels less AR

  Start stop:less fuel used more miles/gallon

  Position of cells : even distribution tyres worn at same rate.

  Aerodynamic: reduces drag
• as a Skydiver jumps?


  w only acting upon person, accelerates. Newton's 2nd Law.
• the skydiver speeds up because

  This is because the AR increases (as long as the AR is less than the weight it accelerates)

  Forces become balanced, reaches terminal velocity.

  Newton's 1st Law.
• Parachute opens?


  AR increases, unbalanced forces. The skydiver slows down. Newton's 2nd Law.

  
• Before skydiver lands


  Slows down, AR decreases till equal to weight it then reaches a second slower terminal velocity. Newton's 1st Law.
• weight is


  the force of gravity pulling your mass down

  
• inertia


  the mass of an object dictates how easy (or difficult) it is to get the object moving to change it's motion