Work Output: Work output is the minimum amount of work that you apply to an object through a certain distance (the amount of work you would apply if you didn't have a machine).
Work Input: Work input is the total amount of work that you apply, including the work output and the friction caused by any moving parts of the machine.
Joules: The unit used to measure work or energy.
Newton: The unit used to measure force.
An example of work output and work input would be a machine that can do 7 J (Joules) of work if 10 J (Joules) of work is put into it. The work input would be the 10 J since that is the amount of work you apply to the machine. The work output would be 7 J since that is the work the machine can produce.
Calculating Efficiency
To calculate efficiency you simply need to divide the useful output work by the input work. Then multiply the work output and work input by 100% to express efficiency in a percentage.
For example, a machine can do 765 J of work if 1000 J of work is put into it. What is the efficiency of the machine? The efficiency of the machine is 80.5%. This is because 80.5% of the work goes towards the useful output work (the work that the machine is designed to do) and the other 19.5% of the work goes to other forms of energy.
You can also calculate the efficiency of a machine by measuring the forces and distances. For example a 200-N box is pushed up a 10-m-long ramp. The person pushing it, pushes with 100 N of force to raise the box to a vertical distance of 2 m.
The efficiency of the ramp would be calculated by first finding the useful output work and input work. Useful output work = (200 N)(2 m) = 400 J Input work = (100 N)(10 m) =1000 J
This work can now be used to calculate efficiency. The ramp's efficiency is 40%. It has a mechanical efficiency greater than 1, and so less force is needed to lift the box. However, some of the work is transferred into heat by friction.Therefore efficiency can never be 100%.
Lastly, to calculate the mechanical efficiency of a lever, you would have to first find out the work input and work output. There are two ways to calculate the work input and work output.
A seesaw is an example of a lever.
1) Multiply the amount of force used to push down or lift up the effort arm (input arm) by the length of the arm (effort arm). To calculate the work output, multiply the weight of the load by the length of its arm.
2) Multiply the amount of force used to push down or lift up the effort arm by the distance which it was moved up or down. To calculate the work output, multiply the weight of the load by the distance which it was moved up or down.
After, divide the work input by the work output and multiply the quotient by a hundred percent since the mechanical efficiency is calculated as a percentage.
For example, a lever has a 10 m input arm with an input force of 80 N (Newtons) and a 5 m output arm that supports a load of 50 N. What is the mechanical efficiency of the lever? The mechanicalefficiency is 62.5%.
Below is a powerpoint explaining how to calculate efficiency.
Home Work Output vs. Work Input Increasing Efficiency Efficiency of Common Mechanisms Quiz Quiz Answers BibliographyWork Output vs. Work Input
Work Output: Work output is the minimum amount of work that you apply to an object through a certain distance (the amount of work you would apply if you didn't have a machine).
Work Input: Work input is the total amount of work that you apply, including the work output and the friction caused by any moving parts of the machine.
Joules: The unit used to measure work or energy.
Newton: The unit used to measure force.
An example of work output and work input would be a machine that can do 7 J (Joules) of work if 10 J (Joules) of work is put into it. The work input would be the 10 J since that is the amount of work you apply to the machine. The work output would be 7 J since that is the work the machine can produce.
Calculating Efficiency
To calculate efficiency you simply need to divide the useful output work by the input work. Then multiply the work output and work input by 100% to express efficiency in a percentage.
For example, a machine can do 765 J of work if 1000 J of work is put into it. What is the efficiency of the machine?The efficiency of the machine is 80.5%. This is because 80.5% of the work goes towards the useful output work (the work that the machine is designed to do) and the other 19.5% of the work goes to other forms of energy.
You can also calculate the efficiency of a machine by measuring the forces and distances. For example a 200-N box is pushed up a 10-m-long ramp. The person pushing it, pushes with 100 N of force to raise the box to a vertical distance of 2 m.
The efficiency of the ramp would be calculated by first finding the useful output work and input work.
Useful output work = (200 N)(2 m)
= 400 J
Input work = (100 N)(10 m)
=1000 J
This work can now be used to calculate efficiency.
The ramp's efficiency is 40%. It has a mechanical efficiency greater than 1, and so less force is needed to lift the box. However, some of the work is transferred into heat by friction.Therefore efficiency can never be 100%.
Lastly, to calculate the mechanical efficiency of a lever, you would have to first find out the work input and work output. There are two ways to calculate the work input and work output.
1) Multiply the amount of force used to push down or lift up the effort arm (input arm) by the length of the arm (effort arm). To calculate the work output, multiply the weight of the load by the length of its arm.
2) Multiply the amount of force used to push down or lift up the effort arm by the distance which it was moved up or down. To calculate the work output, multiply the weight of the load by the distance which it was moved up or down.
After, divide the work input by the work output and multiply the quotient by a hundred percent since the mechanical efficiency is calculated as a percentage.
For example, a lever has a 10 m input arm with an input force of 80 N (Newtons) and a 5 m output arm that supports a load of 50 N. What is the mechanical efficiency of the lever?
Below is a powerpoint explaining how to calculate efficiency.