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Mechanical Advantage: Trading Distance for Force
Definition
Mechanical Advantage
The ratio of output force to input force in a mechanical system.
- Mechanical advantage (MA) is the factor by which a machine multiplies the force you put in.
- An MA greater than 1 means the machine gives out more force than you put in, and an MA less than 1 means it gives out more speed or distance instead.
Note
$$\text{Mechanical Advantage (MA)} = \frac{\text{Load}}{\text{Effort}}$$
- Load is the force the machine moves, and Effort is the force you apply.
- Because MA is a ratio of two forces, it has no units.
- For a lever you can get the same answer from the geometry, by dividing the effort arm by the load arm.
What Mechanical Advantage Buys You
- It reduces the effort needed to move or lift something.
- It increases the output force you get for a given input.
- It lets a person do work that their own muscles could never do unaided, which is why a bottle jack lets one hand lift a car.
Common Mistake
- Mechanical advantage does not create energy, it redistributes it.
- The force is multiplied, but the distance over which you apply it is divided by the same factor.
- That is why the jack handle moves a long way while the car rises a few millimetres, and energy is conserved.
The Simple Systems That Deliver It
- A handful of simple systems are the building blocks every complex machine is assembled from.
- Each one improves function and efficiency in the same way: it lets a smaller effort do a bigger job.
Inclined Plane
Definition
Inclined Plane
Spreads force over a longer distance, making it easier to lift or move objects.
