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Car Acceleration

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Hi, I've been reading an article on car physics (cant find the link though). It says that the force pushing it forward is the engine force multiplied by the unit velocity vector. It then goes on to calculate resistance from tyres and air, then calculate the overall force pushing it forward by adding it all together. It then goes on the say that you then calculate the acceleration by dividing this force by the mass... But what i dont understand is, if the car's starting from rest, then there is no velocity, and hence no force pushing it forward. But if the acceleration is calculated using the overall force, how are you meant to get the car moving in the first place? According to what it says, there's no acceleration without velocity, and obviously there's no velocity without there having at one point been acceleration. It just doesnt make any sense to me, and i cant figure out how to get it to work, so can someone explain it please? I'm also not sure if the Engine force is meant to be a constant or a variable.... But anyway, thanks for any help --Helicon56. [EDIT: here's the link] [edited by - Helicon56 on February 8, 2003 8:58:13 AM]

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Guest Anonymous Poster
well when you push the pedal the motor will generate a force on the wheels

and force sort of equals accerleation (mass is a constant)
F = m.a
then you can get : a = F / m

en then update the new velocity with the accerelation
v = v + a

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Yeah i''ve done that it''s just working out the force in the first place.

But i think i''ve actually just misread it. It says a unit vector in the car''s heading, which i took to mean a unit vector of the car''s velocity. I''ll give using just the way it''s pointing, see if that works....


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There most certainly is acceleration without velocity. You are currently being accelerated towards the center of the earth at -9.81 m/s^2. However, you are being accelerated away from the center of the earth by the floor (chair, etc..) at 9.81 m/s^2, due to the force of electrostatic repulsion.

But I digress. For a car moving from a stop,

Speed = (EngineForce / MassOfCar) * Time

Now take the Speed and multiply it by the Velocity Unit Vector (A vector that only gives direction) and you''re good to go. Now naturally, the car probably won''t be constantly accelerating, so you''ll probably just add (F/M) to Speed every iteration.

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