The scissor jack needs the maximum input force at its lowest position, similar to the principle of levers. If you consider an "ideal structure" with components of zero thickness, the scissor jack at its bottom position will need an infinite force applied horizontally to make it begin to rise vertically.

An analysis of the force is shown in Scissor Lifting Elevator Mechanism, which summarises:

The maximum force needed when the angle theta [between the struts] is minimum.

This is distinct from the pitch of the screw used to raise it, the force from which is independent of the height raised.

Frankly, the scissor jack isn't a very good design. There are other designs that need a constant force regardless of the height raised. In the days when I carried a tool box in my car, it would include a simple hyraulic jack.

The scissor jack needs the maximum input force at its lowest position, similar to the principle of levers. If you consider an "ideal structure" with components of zero thickness, the scissor jack at its bottom position will need an infinite force applied horizontally to make it begin to rise vertically.

An analysis of the force is shown in Scissor Lifting Elevator Mechanism, which summarises:

The maximum force needed when the angle theta [between the struts] is minimum.

This is distinct from the pitch of the screw used to raise it, the force from which is independent of the height raised.

Frankly, the scissor jack isn't a very good design. There are other designs that need a constant force regardless of the height raised. In the days when I carried a tool box in my car, it would include a simple hydraulic jack.

The scissor jack needs the maximum input force at its lowest position, similar to the principle of levers.

  If you consider an "ideal structure" with components of zero thickness, the scissor jack at its bottom position will need an infinite force applied horizontally to make it begin to rise vertically.

Frankly, the scissor jack isn't a very good design. There are other designs that need a constant force regardless of the height raised.

The scissor jack needs the maximum input force at its lowest position, similar to the principle of levers. If you consider an "ideal structure" with components of zero thickness, the scissor jack at its bottom position will need an infinite force applied horizontally to make it begin to rise vertically.

An analysis of the force is shown in Scissor Lifting Elevator Mechanism, which summarises:

The maximum force needed when the angle theta [between the struts] is minimum.

This is distinct from the pitch of the screw used to raise it, the force from which is independent of the height raised.

Frankly, the scissor jack isn't a very good design. There are other designs that need a constant force regardless of the height raised. In the days when I carried a tool box in my car, it would include a simple hyraulic jack.