Force to accelerate an object downward faster than g

[Big Tommy C]

Hello all.

I am trying to understand the math behind this and keep getting stuck. If I want to accelerate and object downward,lets say 16 inches in 0.1655 seconds , that would be faster acceleration than gravity. I think 29.67 m/s2, so if I calculate force to accelerate at that rate downward, Do I have to subtract 9.8 m/s2 from my acceleration of 29.67 before I calculate the force? IE 29.67-9.8=19.87m/s2 and then I use that acceleration of 19.87 against my mass to determine the force required?

Hoping for some clarification ,Tom

 

[etotheipi]

I assume the thing is starting from rest and accelerating uniformly, because then you get the $30 \text{ms}^{-2}$ acceleration.

And yes, to determine the additional force you yourself need to apply, you subtract $g$ and multiply by $m$. That's just because $F + mg = ma \iff F = m(a-g)$.

 

[Lnewqban]

Thinking in reverse, in order to accelerate the same mass upwards at a similar rate, you need to add enough extra upwards force to compensate for the downwards force of weight.
The function of that extra force up is only to balance weight: any additional up force will be the only one contributing to up acceleration.

$a=F_{resultant}/mass$

Always think of acceleration as a result of applying a resultant force onto a mass.

 

[Big Tommy C]

Yes Lnewqban I had this question a while back, I appreciate the response.

I was able to derive that by simply adding the weight of the load plus the force required to accelerate it on a vector would give me my final total F requirement.