yolandasss Posted December 7, 2016 Report Share Posted December 7, 2016 Hi guys! For my IA, I'm investigating on the relationship between time fall a parachute to fall and its surface area, but I can't get a linear relationship. The parachute didn't reach the terminal velocity, so the velocity is changing when the A is changing and it's also accelerating downwards. What can I do? Help please!!!!! Reply Link to post Share on other sites More sharing options...
Guest Posted December 7, 2016 Report Share Posted December 7, 2016 Keep the data and put it into your evaluation? Increase the height, if possible? Reply Link to post Share on other sites More sharing options...
yolandasss Posted December 7, 2016 Author Report Share Posted December 7, 2016 I used logger pro and there seems to be an inverse relationship, but I can't just say it's a relationship because it looks like a inverse graph. I can't increase the height as the parachute won't fall in a straight and the motion detector won't detect it. Thanks anyway! Failling my IA lol Reply Link to post Share on other sites More sharing options...
Guest Posted December 7, 2016 Report Share Posted December 7, 2016 Hm, weird. Anything that can be explained due to external factors? I wish I could help but my Physics knowledge is limited to all that I can remember from ~2 years ago. Reply Link to post Share on other sites More sharing options...
kw0573 Posted December 7, 2016 Report Share Posted December 7, 2016 Surface area impacts resistance force. Without giving away too much, you should graph surface area against an expression of (average?) air resistance, where the time you measured is due to the net force = gravity - air resistance. When we did the lab, we measured velocity so we could differentiate to get acceleration-time graphs, but you have to be a bit clever with knowing just time. Reply Link to post Share on other sites More sharing options...
yolandasss Posted December 7, 2016 Author Report Share Posted December 7, 2016 40 minutes ago, kw0573 said: Surface area impacts resistance force. Without giving away too much, you should graph surface area against an expression of (average?) air resistance, where the time you measured is due to the net force = gravity - air resistance. When we did the lab, we measured velocity so we could differentiate to get acceleration-time graphs, but you have to be a bit clever with knowing just time. That's what i did. Then I derivate a equation from that and I got t=sqrt(2sm/(mg-drag coefficientxair densityxv^2xA) V is different everytime as the values are really small. The surface areas are like 0.0064, 0.0212m^2 ect. Reply Link to post Share on other sites More sharing options...
yolandasss Posted December 7, 2016 Author Report Share Posted December 7, 2016 1 hour ago, apoello said: Hm, weird. Anything that can be explained due to external factors? I wish I could help but my Physics knowledge is limited to all that I can remember from ~2 years ago. Alg Thanks Reply Link to post Share on other sites More sharing options...
kw0573 Posted December 7, 2016 Report Share Posted December 7, 2016 I am kinda confused. I am not sure what time you a plotting (time before hitting ground?). If terminal velocity hasn't been reached then the equation you derived would not be quite useful. If you goal is figure out the drag coefficient, you should plot some relationship that holds before terminal velocity is reached. Some calculus may be involved. The easiest way is to wait until terminal velocity has been reached and find the coefficient that way. Often, the quadratic drag may be small if terminal velocity does not change much compared to the anticipated time without drag. Reply Link to post Share on other sites More sharing options...
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