laws of motion

• Newton's 1st law

  Without any external force, a body cannot change its state of motion
• Momentum

  A physical quantity representing motion present in a body
• Momentum

  Momentum changes when either the magnitude or direction or both change
• Area under (F-t) graph


  Gives the change in momentum
• Newton's 2nd law of motion

  If a net force acts on the body, it will change the motion and momentum of the body, where the rate of change of momentum is given by the magnitude of the applied force
• Acceleration

  If multiple forces are acting on the body, it will be the net force that changes the momentum of the body
• Rocket Propulsion

  • Rate at which rocket burns
  • Rate at which gases are produced and ejected
  • Rate at which the mass of rocket decreases
• Impulse

  Momentum change
• Newton's 3rd law

  Every action has an equal and opposite reaction
• Action and reaction pairs

  • Same magnitude
  • Opposite direction
  • Act on different bodies
• Free Body Diagram

  • Weight of the body: Force that acts on the body because of the gravitational pull of the earth
  • Normal Reaction: When a body presses against a surface, the surface reacts following Newton's 3rd law, by application of the force of same magnitude perpendicular to the surface
  • Tension present in the string: Restoring force that develops when the string is stretched or compressed
• Friction

  Resistive force that acts between two surfaces in contact having a tendency of showing relative motion
• Static Friction

  • Acts between two bodies at rest with no relative motion
  • More the surface press against one another, greater is the normal force and greater is the interlocking and tendency of motion - no static friction
  • Fext = Fminimum to move; Body on verge to move
• Kinetic Friction


  Acts on two surfaces moving relative to one another
• Angle of repose


  Angle of inclination, beyond which a body placed on that incline surface slides down
• • friction exists in action reaction pair
  • when two bodies are showing relative motion it is kinetic friction
• when the stretch in string is greater

  • restore force is greater
  • tension is greater
• In static friction :

  • Fext = 0 : no tendency of motion and no static friction
  • Fext < F minimum to move : F external = static friction