# Homework Help: Force = mass x acceleration and related subject

1. Apr 1, 2006

### magic_ghost

Hello,

Simple question.

Is there an equation or set of equations which allow me to calculate how much force/thrust is needed to lift a certain amount of mass or weight?

Daniel

2. Apr 1, 2006

### moose

If you are lifting it at a constant velocity upwards, then just use f=mg. So you use g as your acceleration, since it's the "acceleration due to gravity".

EDIT: If you are accelerating something upward, then just add the acceleration upward to g.

3. Apr 1, 2006

### nrqed

Unfortunately, this is too vague to answer. It depends what you mean...Is the object lifted at constant velocity? Is it accelerating? Is the object lifted near the surface of the Earth? And on and on...
With a more detailed situation, we could give you explicit formula.

4. Apr 1, 2006

### magic_ghost

So to be more specific,

I am thinking of making a small hovercraft which can support the weight of one person (i.e. 140 pounds).

I know I will need a fan to produce the thrust but in order to know how powerfull the fan needs to, I will need to know how much thrust is required to lift 140 pounds.

Thankyou

Last edited: Apr 1, 2006
5. Apr 1, 2006

### nrqed

Working in SI units, the thrust you need to barely lift the person is simply (mass of hovercraft + mass of the person) times 9.80 m/s^2. A pound is really a unit of weight (not mass) so if the person plus hivercraft weight one thousand pounds, you need one thousand pounds of thrust, minimum.