How much force needed to partialy lift object?

[JamesGreen]

Hi,

Imagine you have an object where the weight is equally divided. What would be the formula to calculate the force needed to lift the object up to a distance without lifting it up completely. For example, a push-up, your feet keep touching the ground but you push your self up. How would one calculate that? If the mass, length, height and standard gravity are known?

Thanks in advance

 

[Stonebridge]

Welcome to the Forum.
If the weight is uniformly distributed along the length of the mass, like a metal rod, for example; then the force you would need to apply to the one end, the other staying on the ground, would be exactly half the weight.
Proof using moments of force about the support point on the ground gives mg x L/2 = F x L where L is the length of the rod.
Diagram can be provided if you want one!

 

[JamesGreen]

Thank you!