Force Calculation Using a Square Threaded Jack Screw

How to calculate the force required to lift or lower a 4 kN load using a square threaded jack screw?

(i) What is the mechanical advantage formula for a screw jack?

(ii) What is the effective mechanical advantage in this case?

Mechanical Advantage Calculation:

The mechanical advantage of a screw jack is given by the formula:

Mechanical Advantage (MA) = Diameter of load-bearing face / Pitch of the screw

Effective Mechanical Advantage Calculation:

Effective MA = MA / (1 + friction coefficient)

When dealing with a square threaded jack screw with a coefficient of friction of 0.1 and a lever length of 70 cm, we can calculate the force required to lift or lower a load of 4 kN by applying the principles of mechanical advantage. The mechanical advantage formula for a screw jack is defined as the ratio of the diameter of the load-bearing face to the pitch of the screw.

In this case, the mechanical advantage can be found by dividing the diameter of the screw (5 cm) by the pitch of the screw (2.5 cm), which results in a mechanical advantage of 2. Taking into account the friction coefficient, the effective mechanical advantage is then calculated by dividing the mechanical advantage by 1 plus the friction coefficient (0.1), giving us an effective MA of approximately 1.818.

To lift the 4 kN load using this effective mechanical advantage, the force applied at the lever end can be determined by dividing the load by the effective MA, resulting in a force of around 2203.96 N. When lowering the load, the force required will be slightly less due to the direction of motion, but the difference is minimal in this scenario.

For a more in-depth understanding of force calculations and mechanical advantage, you can explore further resources on this topic.