### 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

• 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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