In a screw jack, the effort required to lower the load is less than the effort required to raise the same load.
An ideal machine is that in which there is no dissipation of energy in any manner. In an ideal machine, the work output is equal to the work input, i.e., efficiency of an ideal machine is 100%.
In ideal machines mechanical advantage is equal to velocity ratio.
the mechanical advantage of a lifting machine is the ratio of load lifted to the effort applied.
The efficiency of a lifting machine is the ratio of
output to the input
work done by the machine to the work done on the machine
mechanical advantage to the velocity ratio
An ideal machine is that in which there is no dissipation of energy in any manner. In an ideal machine, the work output is equal to the work input, i.e., efficiency of an ideal machine is 100%.
In ideal machines mechanical advantage is equal to velocity ratio.