Recent content by yuiop

As I understand it, P1 cannot drop lower than absolute zero pressure, but it can drop lower than than atmospheric pressure, which is why venturi tubes can produce a vacuum. U1 does not increase without bound and as P1 gets close to absolute zero, U1 and U2 both slow down while maintaining the...

Actually, the overall gear ratio might be something like 10:1. In this chart for the Tesla Roadster that you posted in #57, the overall gear ration is quoted as being 8.28:1 and the revs at 100 mph are about 12000! (Much higher than a geared petrol engine). From the specifications in the...

220 Nm is the torque (T) and and not the force (F) in Newtons. The force in the example you give is F = P/V = 63000 W / 9.16 m/s = 6877 N so you are right that F = k = Constant for ##V<=V_c##. The Force can also be found from F=Energy/distance = E/s. First we need to know the time to...

Actually, I found the power curve diagrams useful to make an improved predicted 0-60 time. Here is how it works. Looking at the curve for the Zoe it can be seen that the power is a linear function of the speed up to a critical speed (##v_c##) which in this case is about 30 km/h or 9.16 m/s. It...

Basically we equate the input energy over the acceleration period to the final kinetic energy, so; ##Pt = \frac{1}{2}Mv^2## \Rightarrow t = \frac{1}{2}\frac{Mv^2}{P} If P is the maximum power and if this could could be delivered right from zero mph then the time given by the above...

Thanks! Now we are getting somewhere. That is a good place to start.

If it's a real world example, how come the parameters are un-physical? Did you really measure a flow of 1 m/s at the inlet with a pressure of 200 kPa? It would be interesting to know what the real world example is and what was actually measured.

If I said I had 4000 kg electric vehicle with a 2 hp motor that did 0 to 60 mph in 3 seconds on the flat without a following wind, you would say that not physically possible. Even if you did not know the drag coefficient or gearing ratio or drive train efficiency of the vehicle, you would still...

Where did you get that definition? Can you quote a source? How exactly are you defining external and internal. In my last post a pointed out a couple of interpretations of those terms. Which interpretation are you using?

Hey WBN! When did you last clear out your mail inbox? Tried to send you a pm ;)

Your welcome ;) It might help to note that Bernoulli's equation is basically a statement of energy conservation. The expanded equation for a vertical funnel that includes head pressure is: ##\frac{v^2}{2}+gh+\frac{p}{\rho} = Constant## Multiplying through by the mass of the volume element...

It might help to imagine that the piston is initially locked in place before the heating takes place. After heating, the pressure in the cylinder is noticeably greater than the external pressure. The piston is released and the volume expands rapidly accelerating the piston. If the piston has...

If the funnel has a circular cross section then the area would be ##\pi*100 m^2## at the inlet and the flow would be ##\pi*100 m/s## at the outlet. To avoid complicating things I will assume a square cross section with sides of 10m and 1m at the inlet and outlet respectively and stick with your...

This equation predicts a 0 to 60 mph time of 7 seconds for the Tesla S performance and 7.2 seconds for the Performance Plus, yet the Plus has significantly more power and torque and the same weight. Something not right there. Tesla claim 5.4 seconds for the Performance and 4.2 seconds for the Plus.

I agree. Here is my simplified formula (for electric cars) obtained by finding the best fit in Excel: ##t_{60}=\frac{2.79 m}{P^{0.46}T^{0.72}}## where m is the kerb weight in Kg, P is the max power in kW and T is torque in Nm. This is a table for performance of electric cars obtained from an...