Recent content by andyfive

Many Thanks Mentallic. I think I may have solved this. I have taken the inverse of the Drag force equation : ##F_{D}=\frac{1}{2}\rho v^{2}AC_{D}## which gives: ##v=\pm \sqrt\frac{2 F_{D}}{\rho A C_{D}}## By working out what v is using this method at let's say t=1, I have then used the...

Yes @ChineseSmeagol, basically this is correct but the ball is in not rolling. it is in free flight with only air resistance. The initial velocity (at t=0 is the maximum velocity) with it decreasing thereafter. See my previous post for details. Many Thanks, Andy.

Many thanks for your replies everyone. I'm am not thinking of a gravity only model. I am using a 'drag force' model : ## F_{D}=\frac{1}{2}\rho v^{2}AC_{D} ## The fixed values I am using are : ## \rho ## = 1.175799 A = 0.001432m ## C_{D} ## = 0.5 with v being variable. To simplify things...

Thanks for your reply Orodruin. In response to you question, i am assuming that the object and all external factors are identical. The only variable is the initial velocity of the object. My question is not really object specific, more a question of can the initial velocity of an (any) object...

Hi, Quick Qustion : If an object is propelled through the air (e.g. a ball is thrown), once the ball has left the throwers hand it will immediatly start to have negative acceleration (at least in the x plane). If the negative acceleration is measured at the same point in time after the ball...

Thanks for your reply Benit13. I see what you are saying. Effectively, working backwards from the results in figure 5 to obtain R1. I have not come across the term 'weight ratio' (or as you describe it, fitting constant). They do not seem to explain how they have derived these 'weight...

Hi, I am trying to understand an equation which I have come across for determining a coefficient based on the size of dimples on a golf ball : CD_Size = R1·(-3.125·(c/d)+0.25) In the description, it indicates that R1 indicates a weight ratio of CD_Size. Can anyone please explain what...

Thanks for your reply mfb. If I understand correctly, a 3 axis accelerometer would measure the translational acceleration in all 3 axis even though the ball is rotating but not the rotational velocity. How would a second 3 axis accelerometer measure different values to the first one? Would...

Hi, Please could someone explain how they think an accelerometer would work if positioned within the center of a freely rotating sphere (e.g a kicked football)? If using triple axis accelerometer and the ball was kicked from a standstill but with no spin, I would imagine that the...

Brilliant. Many Thanks I like Serena. You really have helped clarify things for me. I'll get back to the spreadsheet and see what results I now obtain.

Thanks again I like Serena. Yes, you are absolutely correct, the v will need to be defined actually as sqrt(vx2+vy2+vz2) - this is a model for a 3 dimensional ball flight. The initial velocity(v) at time(t) = 0 is known and hence the three initial velocity vectors are known. Not sure what...

Many Thanks for your reply I like Serena. If I understand correctly, by defining y = ax I get : dy/dt = -FDy/mv If y' is equal to dy/dt then it is as simple as saying y' = -FDy/mv. Is this correct? Thanks

Hi, Hi. I am trying to enter some differential equations into a Runge-Kutta 4th order spreadsheet which requires input in the form y' = ...? My differential equations are in the form : dvx/dt = -FDvx/mv (i.e relate velocity derivative with respect to time to acceleration). Can anyone...