Energy Work and Mechanical Efficiency How do you

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Energy, Work and Mechanical Efficiency How do you measure mechanical efficiency?

Energy, Work and Mechanical Efficiency How do you measure mechanical efficiency?

Mechanical Efficiency �Mechanical efficiency is a comparison of the useful work or energy that

Mechanical Efficiency �Mechanical efficiency is a comparison of the useful work or energy that a mechanical system produces to the work or energy that was put into the system. �Efficiency is written as a percentage, and can be calculated as follows: mechanical efficiency (%) = _output energy (or work)_ × 100 % input energy (or work) �We want machines to have a high level of efficiency so that we waste less energy performing everyday tasks.

Mechanical Efficiency � No machine is 100 % efficient. � Even simple machines experience

Mechanical Efficiency � No machine is 100 % efficient. � Even simple machines experience small amounts of friction and slippage. � Complex machines are made of many simple machines, so the friction and slippage accumulates, making the complex machine less efficient than its individual parts. � Energy can be lost from slippage or friction. pulley Wheels and axles levers

Pulleys � Many work sites use pulleys to move objects. � For example, a

Pulleys � Many work sites use pulleys to move objects. � For example, a crane has a pulley system. � This pulley system can be used to lift heavy objects to great heights. � A pulley system that is old and rusty will not be very efficient. (friction) � A new pulley system that moves easily is more efficient.

Levers �Levers are usually quite efficient. �When the bar is rigid and the fulcrum

Levers �Levers are usually quite efficient. �When the bar is rigid and the fulcrum is hard and slightly pointed or rounded, there is minimal friction and little energy is lost. �However, sometimes even simple machines are inefficient.

CHECK YOUR LEARNING 1. Use a Venn diagram to compare the everyday meaning

CHECK YOUR LEARNING 1. Use a Venn diagram to compare the everyday meaning of efficiency from last lesson and its scientific meaning from this lesson. 2. How efficient is a pulley system if an operator has to pull 4. 0 m of rope to raise a 250 N pail of water a distance of 2. 0 m? The operator is pulling with a force of 150 N. 3. A block and tackle is a rope and pulley system that uses multiple pulleys. It multiplies a small force into a large one. If a motor has a weight of about 2500 N and people pull 4. 0 m of rope with a force of 700 N to raise the motor 1. 0 m, how efficient is the block and tackle? 4. Name something you can do to increase the efficiency of your bicycle.