# How is lift force proportional to speed up?

1. Mar 21, 2013

### thebluser

i know that if i have a greater lift force, there will be a greater speed upwards, but i don't know to calculate a speed of something upwards. is this even possible to calculate? if it's not, can you give a calculation example??

2. Mar 21, 2013

### CWatters

Work out the net force acting on the object in the vertical direction..

Net Force = Lift - Weight

Then apply Newton..

Net Force = mass * acceleration

If lift = weight then there is no net force acting on the object so it's vertical velocity will be constant (eg acceleration = 0).

3. Mar 21, 2013

### thebluser

is weight the atmospheric pressure or how much the body weighs? just want to make sure.

4. Mar 21, 2013

### rcgldr

By definition, lift is perpendicular to the direction of travel (with respect to the air), so it only changes direction, not speed. If a plane is in a steady vertical climb at some constant angle θ above horitzontal, with a vertical speed component of speed x sin(θ), then there needs to be enough thrust and lift so that the vertical components of thrust and lift equal the weight of the aircraft:

thrust x sin(θ) + lift x cos(θ) = weight.

5. Mar 21, 2013

### thebluser

okay then, thank you all!