Chap 9

• Define a force


  a force is a push or pull upon an object resulting from the objects interaction with another
• SI unit of force

  Newton
• Effects of forces

  -Motion

  -turning effect

  • size / shape
  • pressure
• What is the turning effect


  Turning effect of a force, or defined as the ability to make something turn. Larger turning effect can be produced by applying force at a further distance from the pivot or a larger force
• What are the factors affecting turning effect

  Force applied

  dist. Of application of a force to pivot
• What is pressure

  Pressure is defined as the force acting per unit area
• Formula for pressure

  P=F/A

  pressure= force/ area which the force is acting on
• SI unit of pressure

  SI unit of Force : N

  SI unit of Area : m2

  thus N/m2 or Pa or pascal in words
• Sharp vs dull cut more easy

  Sharp knife has a smaller contact surface so more pressure will be applied by the sharp knife even though the same amount of force applied on each knife.
• What is energy

  Energy is the capacity to do work
• SI unit of energy


  Joules
• What is work done

  Work done by a constant force on an object is given by the product of the force and the distance moved by the object in the direction of the force.
• Formula for work done


  F x d.
• SI unit for work done


  Joules
• What is GPE

  Defined as the energy which a body possesses bc of its position relative to the ground
• Formula for gpe


  Gpe=m g h

  mass in kg x grav field strength in N/kg (10N/kg) x height in m
• what is kinetic energy


  Defined as the energy possessed by the object due to its motion
• Formula for kinetic energy


  KE= 1/2 m vsquared

  mass in kg x speed in m/s
• Principle of conservation of energy


  Energy can neither be destroyed nor created in any process. It can be converted from one form to another or transferred from one body to another, but the total amount remains constant
• Noncontact forces


  Gravitational, magnetic, electrostatic
• Contact forces 


  Applied, friction, tension, spring, drag, contact
• Friction


  Opposes motion between two surfaces in contact
• Elastic force


  The force acting on a stretched or compressed elastic object to return it to its original shape
• Tension


  Force that is transmitted through a string, rope, cable or wire when it is pulled tight by forces acting from opposite ends.
• Applied force 


  Applied to an object by a person or another object
• Drag 


  Special type of frictional force that acts upon objects as they travel through the fluid
• Electrostatic force 


  Force that exists between all charged particles
• Magnetic force 


  Push or pull exerted by a magnet
• Gravitational


  Force exerted by a planet on to an object
• factors affecting turning effect


  1. force applied 2. Distance of applications of a force to pivot
• Larger turning effect can be produced by applying

  • force at a further distance from the pivot - a larger force
• Si unit of energy


  Joules
• For work to be done…

  A force is applied on the object & the object moves in the same direction as the force applied on it