# Homework Help: Forces in Equilibrium

1. Nov 23, 2005

### The Bob

Hi all. I have a strange problem.

I have been doing my physics investigation and I decided (with some arguments) to test forces in equilibrium. I need to know a formula to ensure my results are more or less accurate. Let me give you a low-down of the set up.

A sail, made of paper, is stuck on to a metal 'boat' that goes on an air track. Cotton is then knotted to the 'boat' and passed through a pulley that allows the cotton to be attached to weights (vertical) that will pull the 'boat' to the end of the air track that is nearest the pulley. A fan, at the same end, is then turned on and the distance that the 'boat' moves, due to the fan blowing on the sail, is measured from the fan (the source).

I, therefore, know the force that the fan is acting on the sail, as it is equal to the weight of the boat and the masses, the distance from the source and the area of the sail.

I have tried to find a constant from my data and tried the internet for this information but all I get is sails on yachts.

Can anyone even try to help me? I cannot find anything and cannot make any connections with different equations.

I you do not feel I have written enough about what I have done or what I think then say so and I will add some more.

Cheers.

2. Nov 23, 2005

### Astronuc

Staff Emeritus
Are you looking for something along the lines of drag force?

I imagine though that the wind velocity decreases by the distance from the fan, so the force of the wind is a function of distance along the track.

Also the coefficient of drag is dependent on the absolute velocity between the object and opposing flow.

What measurements/experiments have been done, i.e. same pulling force with and without wind? Or did you use different pulling masses.

Have you tried measuring the velocity of the wind from the fan?

And - what equations have you developed?

3. Nov 23, 2005

### The Bob

The fan has 3 settings. Each gives a different wind velocity.
I have measured the distance from the source. I have used different areas and shapes of sails. The masses pulling the 'boat' varied by 10 grams each. Each experiment was done with wind.

I have not tried measuring the wind velocity, didn't really think about it. And I cannot think of an equations I can use to develop an equation at all. If we added wind velocity, e.g. the setting on the fan, could an equation be found?

Cheers.