Simple machine — Science definition
A device that changes the size or direction of an applied force.
Where it is taught
- Levers, Ramps & Pulleys — Work & Machines, Physical Science: Matter, Forces & Energy, Grade 8
Questions using simple machine
Problem 1
A simple machine makes a task easier mainly by
- reducing the work needed
- changing the size or direction of the force
- creating energy
- removing friction
Answer and explanation
changing the size or direction of the force
The work is at best the same; the machine trades force against distance.
Problem 2
Explain why a simple machine cannot reduce the total work that has to be done.
Answer and explanation
Work is force times distance, and a machine reduces the force only by increasing the distance over which it acts, so the product stays the same at best. In practice friction means the work put in is slightly more than the useful work got out. A machine makes a task manageable, not cheaper in energy.
Response criteria
- State a scientifically accurate conclusion.
- Show the data, mechanism, or calculation that supports it.
- Include units, conditions, or limits where relevant.