Drag Force on a Coffee Filter

Lab Report #7 Drag Force on a Coffee Filter

Purpose:

to study the relationship between air drag forces and the velocity of a falling body.

Procedure: Using a packet of nine coffee filters, Logger Pro software and motion sensor we measured the drag force of the paper filters. To make sure that our results were more accurate and consistent we made sure the shape of the packet of filters stayed the same throughout the experiment.

This is because drag is affected by the surface area of the object as well so, the greater the surface area the greater the drag force will be and vice versa, the smaller the surface area of the object the smaller the drag force will be therefore, to keep a somewhat constant surface area it is important to keep the shape for all the filters the same. If the filters were separated then the data collected from the results of the experiment would not be as accurate or precise.

We let the filters fall from a height of 1.5 m right above the motion detector; we collected the data from each of the nine coffee filters, removing one at a time, five different runs each. My first prediction on how the graph would look like was that it would be a curve concave down, similar to the graph of gravity because I acceleration was still involved. After the experiment I found that the correct graph looks sort of linear and that the Speed is actually constant.

We examined the position vs. time graph obtained with the help of Logger Pro, selecting a small range of data points near the end of motion where the pocket moved with constant speed; we excluded the points where the motion was not uniform. Using the linear curve fit feature in Logger Pro (y=mx + b) we found the slope of the graph to be -0.8068 m/s The slope represents a constant velocity, which is the velocity of the drag.

We also created a second graph using Logger Pro with number of filters vs. average terminal speed. By using the Power law fit of the data we recorded the power "n" given, n=2.070 and we found that our percent error was 3.5% based on our calculations using the %error formula: ((real-exp.)/(real))x100% where  the real/accepted value for “n” is 2.00

 

 

 

Conclusion:

 Based on our observation we have concluded that drag is directly proportional to weight of the packet and consequently drag force depends on the speed of the object. Comparing drag force equation Fdrag= ¼(Av^2), to equation Fd=kabs[v] ^2 1 from the Lab we determined that exp=2= air drag accepted value, k=A=some constant and v=Average velocity. The fit parameter represents the some of the key points we already talked about. For example, Graph number 2 shows the relation between average velocity and the # of coffee filters/ weight; we can say that as the # of coffee filters/weight increase, the average velocity increases too.

Some of the sources of greater error or areas where the experiment could be improved to obtain more accurate results from the experiment would be to drop the coffee filters at the same height, the same way each time. Also, the pack of coffee filters may not have been exactly the same for each run because the filters would impact the floor each time and they might have suffered some deformation so, the air drag would slightly change each time in a way that might not have changed if the surface area of the packet was not disturbed.