for the car nuts again

[tris-]

currently designing a spreadsheet model (which some may remember my previous questions from months ago) which is on stopping distances from cars. ive pretty much sussed all the shit out except one thing.

the engine force. the engine force im given for this made up car is a maximum of 8000N. am i correct in believing that all this dictates is the maximum velocity the car could obtain? the other made up car is question marked on its engine force, which is making me think it could also have an impact on something else as well.

 

[UrganNagru]

Not much of a car nut but having difficulty working out how you could work out breaking distances or velocity with just the force if you had the power of the engine at that point you could use P=FV to work out velocity, then if you knew the force on the break the weight of the car and the friction co-efficient of the brakes and tyres you could then try to calculate the resistive force and so the resultant force then using F=MA calculate the the deceleration.
Of course this could all be totally irrelevant to what you asked, you coulduse it to work out the maximum velocity if you know how air resistance relates to the cars speed, if not again you need the power of the car when it exerts maximum force.

 

[tris-]

im not working out stopping distance based only on engine force. i just want to know what engine force signifys in relation to how the car works.

 

[leggy]

Force (your 8000N) will not dictate the car's maximum velocity. It will however dictate it's maximum acceleration.

 

[tris-]

Force (your 8000N) will not dictate the car's maximum velocity. It will however dictate it's maximum acceleration.

so my car weighs 1000kg, if im not mistaken its max accel is 8 m/s/s.

maybe im being stupid, but if im only calculating stopping distances and stopping distances with variable masses added, i cannot see a reason why id need to know that.

though ofc i know with more weight its max accel will decrease

 

[leggy]

so my car weighs 1000kg, if im not mistaken its max accel is 8 m/s/s.

maybe im being stupid, but if im only calculating stopping distances and stopping distances with variable masses added, i cannot see a reason why id need to know that.

though ofc i know with more weight its max accel will decrease

You might need to know it in order to calculate the mass of the car (if you don't already know it).

The force that the engine can produce has no bearing on deceleration. That will be mass and brakes (co-efficient of friction etc.)

 

[UrganNagru]

Maximum force will dictate a cars maximum velocity as air resistance is relative to the cars velocity, so when the car is going at a velocity which causes the resistive forces to be equal to the cars maximum force it will have reached its maximum velocity, as there will be no resultant force and hence no acceleration.

 

[tris-]

thats for the help.

i tried asking the tutor at uni but hes as much help as predicting the future from a pile of feces :\

 

[UrganNagru]

Hehe no problem, what subject is it by the way? If you can send a copy of the question/data, I could try and see if I could make head or tale of it.

 

[tris-]

Hehe no problem, what subject is it by the way? If you can send a copy of the question/data, I could try and see if I could make head or tale of it.

its some scientific skills / physics / ICT module of my degree.

ive got it pretty much sussed now though. most questions i asked months ago and only just now i could be arsed to do it cheers though.

but if you like you can have the info, if you have nothing to do some rainy day

 

[UrganNagru]

Hehe its a sad state of affairs when I'm tempted to have a shot at someone elses course work when I've got a months back log of assignments for my feckin' apprenticeship

 

[Tom]

Engine force can have a minor impact on stopping distances if engine braking is brought into consideration.

Bear in mind that the engine forces quoted for most cars are at the flywheel. The force at the driven wheels is often 80-90% of that figure as the difference is absorbed by the drivetrain.

Engine force is not the sole dictator of acceleration or velocity. In some cars the maximum velocity is dictated by the gearing. An engine might run out of power at a high rpm with a 1:1 gearing at 150mph, but if you changed the gearing to 1:2 you may put the engine back into its most efficient rpm range where the available torque is higher - and you'll get more velocity. Not a lot though, as aerodynamics are a powerful limiting factor at high speeds.

This is really a question that needs to be asked on pistonheads tbh. Theres an engine-specific forum, they all design engines and stuff in there.

 

[tris-]

thankfully i dont go into that much detail. ratios and air resistance and all that jazz is not included (the whole thing is made up and doesnt need extensive details).

i just needed to know basically what its for

 

[Tom]

Are you talking about power, or torque (twisting force)?

 

[tris-]

Are you talking about power, or torque (twisting force)?

no idea, it just says engine force 8000N

 

[old.user4556]

presume it means Nm? which would mean torque...?

 

[Tom]

Its a silly question really, you can't consider the engine output of a car without analysing the gear ratios and transmission losses.

 

[tris-]

Its a silly question really, you can't consider the engine output of a car without analysing the gear ratios and transmission losses.

tom, the whole thing is made up, the cars, their masses, reaction times, its all fake!

we dont need to go into such depth as its not the point in the exercises. i just wanted a vague idea of what it is incase i may need to utilise it.

 

[Tom]

Oi. Its 'Tom' not tom.

 

[tris-]

i will call you what ever the fuck i want

 

[TdC]

not unless you want me visiting

 

[tris-]

not unless you want me visiting

fu

 

[TdC]

you wish

 

[Tom]

i will call you what ever the fuck i want

stfu (stuff you) noob

 

[DaGaffer]

Yeah, that's power, torque would be in Newton Metres. Not that anyone uses Newtons for describing engine power. In a hypothetical exercise, ignoring gearing, resistance losses and aerodynamics, then yes, power would be the ultimate determinant of velocity. I assume you're just going to determine absolute velocity from 1/2MVSqd? as you have the mass and the force?

 

[leggy]

Yeah, that's power, torque would be in Newton Metres. Not that anyone uses Newtons for describing engine power. In a hypothetical exercise, ignoring gearing, resistance losses and aerodynamics, then yes, power would be the ultimate determinant of velocity. I assume you're just going to determine absolute velocity from 1/2MVSqd? as you have the mass and the force?

Power is not measured in Newtons. Force is.

Torque is measured in N.m

The question has obviously been simplified to use straight force rather than torque.