Distance and wind force

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1. Jul 17, 2015

Phylover

I have done an experiment recently and found that there seems to exist a linear relationship (the R-squared value closest to one compared to quadratic fit, although they are pretty close) between the distance from the fan and the wind force.

At distance zero there is a certain magnitude the force and the force just drops by a constant rate when further away (perpendicular to the fan surface) from the fan.

The fan is in front of the object which I measure the acceleration. Any background theory in support of the findings? (just a normal electric fan we use at home)

2. Jul 17, 2015

Dr. Courtney

Interesting, can you post your data in a chart or graph?

Do you have several force readings for each distance allowing a mean and an uncertainty or just one force reading?

Do you have results for more than one fan speed?

I would expect the force to approach zero as an asymptote as the distance is increased.

Lots of functions can be nearly linear over a short span of input values. Think about what might happen at larger distances?

Can the force really be negative as a decreasing line would predict at some distance?

3. Jul 20, 2015

Phylover

Yes, I take three readings at each distance and then take an average of them.
I only have result for one fan speed.
Yes, I also think that it will approach zero as an asymptote as the distance is increased. But at certain distance the wind blown out by the fan cannot put the car into acceleration any more, and that's why I only have seven/ eight data points on my graph.
I don;t think the force can actually be negative because the further away the object from the fan, the smaller the force of pushing it away but it is unreasonable that the force of wind blown out by the fan actually pushes the object towards the fan.

4. Jul 20, 2015

Dr. Courtney

OK, it seems that you are somehow using motion of a model car as a proxy for the "wind force." Are you actually computing a physics "force" are is your dependent variable really something else? You could compute a real net force if you know the mass of the car and measure the acceleration, but then you need to know the frictional force that must be overcome to separate out the wind force.

When communicating results of an experiment, the experimental method, and the independent and dependent variable are very important.

It is hard to suggest background theory without knowing more.