Screw Jack  Effort Force vs. Load
Screw jacks and effort forces.
A screw jack is a mechanical device that can increase the magnitude of an effort force.
The effort force for a screw jack when neglecting friction can be expressed as
F = (Q p) / (2 π R) (1)
where
F = effort force at the end of the arm or handle (lb, N)
Q = weight or load (lb, N)
p = pitch  distance or lead of thread in one turn (in, m)
R = leverarm radius (in, m)
Pitch is the distance between screw grooves and is commonly used with inch sized products and specified as threads per inch. Lead is the linear travel the nut makes per one screw revolution. The pitch and lead are equal.
The torque acting on the screw can be calculated as
T = F R (2)
where
T = torque (lb in, Nm)
Example  Screw jack without friction
If the load on a screw jack is 50000 lb, the leverarm is 20 inches and the pitch equals 1/8 inches  the effort force can be estimated to
F = ((50000 lb) (1/8 in)) / (2 π (20 in))
= 49.8 lb
The torque acting on the screw can be calculated
T = (49.8 lb) (20 in)
= 995 lb in
= 82.9 lb ft
Example  Metric Screw Lift
A M24 metric screw with pitch 3 mm is used in a mechanical screw lift with load 225 kN. The lever arm is 0.5 m. The effort force required can be calculated as
F = ((225000 N) (0.003 m)) / (2 π (0.5 m))
= 215 N
The torque acting on the screw can be calculated
T = (215 N) (0.5 m)
= 107 Nm
Screw Jack Calculator  without Friction  Imperial Units
Calculate torque and effort force acting on the lever arm.
Screw Jack Calculator  without Friction  Metric Units
Calculate torque and effort force acting on the lever arm.
Note the difference between mass and weight!
Screw Jack with Friction
For motion in the same direction as the load (load assist the screw jack), the effort force can expressed as
F = Q ( (2 π μ r  p) / (2 π r + μ p) ) (r / R) (2)
where
r = pitch radius of screw (in)
For motion in the opposite direction as the load (load resists the screw jack), the effort force can expressed as
F = Q ( (2 π μ r + p) / (2 π r  μ p) ) (r / R) (3)
Related Topics

Mechanics
The relationships between forces, acceleration, displacement, vectors, motion, momentum, energy of objects and more. 
Statics
Forces acting on bodies at rest under equilibrium conditions  loads, forces and torque, beams and columns.
Related Documents

Force Ratio
The force ratio is the load force versus the effort force. 
Friction  Friction Coefficients and Calculator
Friction theory with calculator and friction coefficients for combinations of materials like ice, aluminum, steel, graphite and many more. 
Improvised Torque Wrench
Improvise a torque wrench with a luggage scale. 
Levers
Use levers to magnify forces. 
Lifting Wheels
Loads and effort force with lifting wheels. 
Metric Bolts  Minimum Ultimate Tensile and Proof Loads
Minimum ultimate tensile and proof loads for metric bolts with coarse or fine threads. 
Movement Ratio
Machines and movement ratio (velocity ratio). 
Piston Engines  Displacement
Calculate piston engine displacement. 
Shackles  Safe Loads
Safe loads of shackles. 
Toggle Joint
A toggle joint mechanism can be used to multiply force.