Mechanical Advantage refers to the ratio between effort and load of a system/machine. Velocity Ratio refers to the ratio of speeds of the load and effort. Both these concepts are proportional to each other i.e. increases MA increases VR, and vice versa.
Definition
MA (Mechanical Advantage)
Mechanical Advantage conceptually refers to the force amplification of a machine. Machines with high MA (i.e. > 1) amplify the force of the effort by a huge factor. Similarly, machines with lower MA (i.e. < 1) means more effort force is required to produce a load force. It is a scalar quantity, and being a ratio, is unitless.
VR (Velocity Ratio)
Velocity Ratio conceptually refers to the speed reduction (well, technically velocity) of a machine. Higher VR (i.e. >1) results in the load component moving much slower than the effort component. Lower VR (i.e. < 1) results in a faster moving load component, compared to the effort component.
It is very useful to note that , and as such, since the machine operates in the same timeframe (i.e. velocity = displacement) , a lower VR also means the load components moves further than the effort component.
Connection
As mentioned previously, MA and VR are directly linked to another. In an ideal machine, with 100% efficiency, MA = VR. Usually, due to friction and whatnot, that is not the case. But VCAA uses ideal machines, so assume MA = VR.
Calculating MA and VR
Mechanical Advantage
At it’s very essence, mechanical advantage is simply the load force divided by the effort force. As such, the VCAA formula is:
However, this formula can be translated into many other formulas relating to simple machines:
Velocity Ratio
Velocity Ratio, as the name suggests, is the ratio of the velocities of the effort and the load. The formula is:
Applications
High MA
A good, simple example of a machine with high mechanical advantage is a bicycle with on a low gear, such as gear 1. Usually used when moving uphill, and a lot of force is required to overcome gravity, gear 1 amplifies the force. However, the drawback is the high velocity ratio, which means we need to either pedal faster, or do more pedals to move the same distance.
Low MA
So why bother with having a lower mechanical advantage? If a machine’s mechanical advantage is < 1, then it’s VR is also < 1. This means the machine acts as a velocity amplifier, but a force reducer. Again, with a gear-system bicycle, think of the higher gears. Gear 8 require a lot of effort to push, but results in the bike moving much faster.