Science Buddies: "Ask an Expert"

Hey, I was wondering if anyone could help me further analyze my project. My project is that i am trying to find out if using different kinds of skirt materials on my hover craft with change the spped. i used bungie cords to move it to 40 feet and timed how long it takes to get the speed of it.

I'm not quite sure if I understand you correctly, but it sounds like you connected the hovercraft to bungie cords tied to a stationary object. Then stretched the cord back 40 feet and timed how long it took for the hovercraft to travel the 40 ft. Then you took the time it took and divided 40 ft by that to get the average speed over the 40 ft.

That's a good starting point for analysis, but I think you might always want to repeat your experiment and gather more data to more analysys (it is very common to redo an experiment to gather more data). I would suggest trying several different distances. Then graphing these distance in the following way

Speed of Material 1 over 10, 20, 30, 40 ft (red line)
Speed of Marerial 2 over 10, 20, 30, 40 ft (blue line)
...

The that graph, the line that has the highest speed over all the distances can be picked as the best material for speed.

Hope this helps.

Well, i probably should have been more specific. I used bungie cords and tied them to a stationary object, then i hooked up the hovercraft. I then pulled the craft back 4' and timed how long it takes to travel 40'. It averaged from 4mph to 10mph.

Hockeystar129,

This sounds like a great experiment!

In your write-up, are you including the mass (weight) of the hover craft? I ask because while the power to accelerate your hovercraft (stored tension in the bungie-cords) your mass may be different with different experimental skirt materials. Thus, I would could imagine, and would hypothesize, that different mass skirts will effect your experimental results. Specifically, the lighter the total hovercraft mass, the faster it will accelerate.

This brings to mind some things to search... such as "Hookian Spring" force and energy storage. Also the classical acceleration equations may be useful in your analysis of your experiment:

http://library.thinkquest.org/10796/ch3/ch3.htm

One of the ways that scientists make analysis easier is by setting up their experiments so that only one variable occurs at a time. In this case, you may wish to adjust the mass (weight) of the hovercraft by adding or subtracting weight to keep it constant even with different skirt materials.

You may also wish to use your eyes and ears during your acceleration tests. Noise and bouncing around may be indications of the skirt dragging on the ground. You may note a correlation with lack of the noise or bouncing with higher speeds.

Good Luck - Please keep us informed.

Something to keep in mind is to make sure you're weighing down the hovercraft with a consistent mass and that it doesnt really hover over the ground and spring back uncontrollably. You want to make sure it's weighted down enough to drag.

One variable that you will have to account for is the response time you take to stop a stop watch or whatever timing mechanism you are using.

Multiple runs will lower the percentage error. Essentially, make multiple trials with the same fabric and see what kind of times you get.

Good luck. Sounds like a good experiment.

Also, I was wondering if you can help me out mith my other Indepenent Variable. I have 2 of them. My other one that I am testing is The Effect of the Amount of Weight (lbs) on a HOvercraft on the Speed of the Hovercraft. If you could send me a reply as quickly as possible on how to improve my project it would be greatly appreciated. Thank You.

HockeyStar1219

Really quick, this is how I would do the actual test.

Use the same stationary point that your bungee is hooked into every time.

Put a piece of tape on the ground that will consistently be used as the starting point where you will stretch the bungee cord to.

I would use a closed container and the same container for each trial. I would pick up some different weights for the same fabric used and run each weight at least five times to get an average time of travel. You will also need a fairly precise and quick response stop watch. Having a friend help you by using the stopwatch or pulling the hovecraft for you will help immensely. You will want to watch for the impact point from the side. Not looking directly striaght ahead. This gives a better perspective for impact time.

What you need to think about here though, is what is it you're trying to prove. state the principles. Most people can guess which fabric will slide the fastest, but what does this mean? What principles are you trying to prove or demonstrate?