Hi all. I didn't get it cleared although i tried searching the internet. 1) Firstly, how does a vehicle gets off...i mean how the torque is converted into propelling force. I don't want to know the mechanism, gears etc...i want to know the physics... 2) Another question is that whether static friction force is itself the propelling force in this case? And how the friction force varies from the start. Like at t=0, friction force is totally static. Then how does it proceed on. 3) Also what is the condition when wheels start slipping? 4) If I were to design an engine how would I decide what's the torque of engine to propel a vehicle of say mass 'm' and acceleration 'a' Just for simplification i assume that at low speeds the drag force is negligible. 5) Lastly, what's the difference between the terms traction, tractive force and tractive effort? I Googled but everyone has different things to say about it!! And is tractive force equal to [mass x acceleration] of the vehicle? or is it equal to the static friction force. I'm totally confused over this topic. Please, help required. Thanks in advance.