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Using Machines
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1. Machines A machine is a device that makes doing work easier.
Machines make work easier by (a) increasing force (b) increasing distance ‘(c) changing direction
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2. Effort Force Effort force is the force applied to the machines Fe
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3. Resistance Force Resistance force is the force applied by the machine to overcome resistance Fr
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4. Work Done by a Machine Two types of work: the work done by you on the machine and the work done by the machine Input Work: Win – work done by you on the machines Output Work: Wout – work done by the machines
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5. Conserving Energy Recall, energy can not be created or destroyed; it is transferred So, Wout can NEVER be greater than Win; typically Wout is always less than Win because some of the energy changes to heat due to friction
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6. Ideal Machines No friction exists and therefore
Work in ==== Work out
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7. Mechanical Advantage Mechanical Advantage – the number of times a machines multiplies the effort force Calculated by dividing the Resistance Force by the Effort Force
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8. IMA vs MA Difference between ideal mechanical advantage and mechanical advantage is friction. IMA is a calculation assuming no work input is lost to friction and converted to heat. MA takes friction into account and is a realistic number.
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9. Efficiency Efficiency is a measure of how much of the work put into a machine is changed into useful output work by the machines (ie not transferred to heat via friction) Wout/Win * 100%
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