Task 3.3 Appreciate effects of friction on mechanical systems

A screw jack has a square single start thread with a pitch of 5mm and an effective

diameter of 35mm. The operating handle is 0.45m. The coefficient of friction between the

screw and operating nut is 0.25 and the load carried is 250 kg. Calculate:

i.

ii.

III.

iv.

the torque required to raise and lower the load

the efficiency of the jack as a lifting device

its mechanical advantage when raising this load.

If the coefficient of friction is increased in this screw jack, how would this affect the

torque required to raise the load?