- #1
Jonsson
- 78
- 0
Hello there,
Just got an old car, and I was looking at the specifications, and trying to teach myself Newtonian physics. But I cannot get it to work out correctly. Please tell me where I go wrong.
The car weighs 900 kg. The engine has 200nm of torque, it accelerates from still to 27.7 m/s in 8 seconds. The radius from the center of the drive axle to the outside of the tire is circa 0.3m.
F = m\,a
Assuming constant acceleration:
F = m\frac{v}{t}
F = 900\mathrm{ kg}\frac{27.7\mathrm{ m/s}}{8\mathrm{ s}}
F = 3116\,\mathrm{ N}
So, to go from zero to 100km/h in 8 seconds takes 3116 N. This is not taking aerodynamic drag and drivetrain friction into account.
This is where I go wrong I think. The car has 200 Nm of torque:
\tau = 200\,\mathrm{Nm}
I have an arm of 0.3m (the distance from the centre of the wheel to the outside of the tyre)
F = \frac{\tau}{r}
F = 666 N
The problem is 3116\,\mathrm{ N} >> 666\,\mathrm{ N}
And this is without even taken aerodynamic drag and drivetrain losses/friction and all of that jazz into account.
How come my maths is off by so much?
Thank you for your time.
Kind regards,
Marius
NOTE: Looks like my numbers may be off by a factor of 2∏ ? Not sure where it should go though.
Just got an old car, and I was looking at the specifications, and trying to teach myself Newtonian physics. But I cannot get it to work out correctly. Please tell me where I go wrong.
The car weighs 900 kg. The engine has 200nm of torque, it accelerates from still to 27.7 m/s in 8 seconds. The radius from the center of the drive axle to the outside of the tire is circa 0.3m.
F = m\,a
Assuming constant acceleration:
F = m\frac{v}{t}
F = 900\mathrm{ kg}\frac{27.7\mathrm{ m/s}}{8\mathrm{ s}}
F = 3116\,\mathrm{ N}
So, to go from zero to 100km/h in 8 seconds takes 3116 N. This is not taking aerodynamic drag and drivetrain friction into account.
This is where I go wrong I think. The car has 200 Nm of torque:
\tau = 200\,\mathrm{Nm}
I have an arm of 0.3m (the distance from the centre of the wheel to the outside of the tyre)
F = \frac{\tau}{r}
F = 666 N
The problem is 3116\,\mathrm{ N} >> 666\,\mathrm{ N}
And this is without even taken aerodynamic drag and drivetrain losses/friction and all of that jazz into account.
How come my maths is off by so much?
Thank you for your time.
Kind regards,
Marius
NOTE: Looks like my numbers may be off by a factor of 2∏ ? Not sure where it should go though.
Last edited:
