ZIMSEC O Level Combined Science Notes: Machines:Levers

  • A lever is a very simple machine
  • It is made up of a rigid bar resting on a pivot,
  • used to move a ¬†load with one end
  • by applying an effort on the other end
  • Examples of machines that use the lever are:
  • scissors, human arm, hand pump, claw hammer, shovel

 

Components of a lever

Components of a lever

  • using a lever a heavy load can be lifted by exerting a small force on the opposite end
  • mechanical advantage-the ratio of the load lifted to the effort exerted
  • The larger the mechanical advantage the more useful the machine is
  • \text{Mechanical Advantage=}\dfrac{Load}{Effort}
  • In a lever such as the one shown above (crow bar) the effort moves a greater distance than the load
  • velocity ratio-is the ratio of the distance moved by the effort to the distance moved by the load
  • \text{Velocity Ration=} \dfrac{\text{Distance moved by effort}}{\text{Distance move by load}}
  • The work done by the machine depends on the size of the effort(force) applied
  • and the distance it moves
  • \text{Work(in Joules)=Force x Distance}

Efficiency

  • With every machine the work done by the machine cannot exceed the work output by the machine
  • This is because some of the energy input is lost by friction
  • This becomes heat energy
  • Efficiency is the ratio of the useful work performed by a machine or in a process to the total energy input
  • It can be calculated using the equation
  • \text{Efficiency= }\dfrac{Output}{Input}
  • This can also be expressed as:
  • \text{Efficiency= }\dfrac{\text{Work done on load}}{\text{Work done on effort}}
  • In levers this can be found using the formula:
  • \text{Efficiency= }\dfrac{\text{Load x Distance moved by load}}{ \text{Effort x Distance moved by effort}}
  • The efficiency is then expressed as a percentage
  • Note that the lever need not be in the middle
  • In a wheelbarrow for example the wheel is the pivot
  • This means the lever can be at the end

To access more topics go to the Combined Science Notes page


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