friction and terminal velocity of a parachutist vs a car

[raaaid]

friction in a fluid is:

force of friction=k*h*v where k is a constant that depends on the fluid , h depends on the shape of the object and v is the velocity the object has

so you can see if the object is acelerating v will grow eventually getting to be equal both the force that causes the aceleration and the force of friction reaching the terminal velocity that a parachutist fro example reaches

but on a surface its different:

force of friction=normal force*MU, where mu is a constant

but the problm here is that this means that if you apply to an object a force bigger than this force of friction it will be acelerating for ever(force applied-force of friction)= m*a (f=ma which btw is also proved wrong by relativity)

so in this case terminal velocity is NOT reached

this teaching on friction is universal and FALSE

oh god im wishing so much to finish my studies to dedicate my time to art

[ACE-OF-ACES]

Originally Posted by raaaid

oh god im wishing so much to finish my studies to dedicate my time to art

And in light of your post you may want to consider finishing that physics 101 online class for kids at the NASA site.. Just a thought

[GraveyardJimmy]

Originally Posted by raaaid

friction in a fluid is:

force of friction=k*h*v where k is a constant that depends on the fluid , h depends on the shape of the object and v is the velocity the object has

so you can see if the object is acelerating v will grow eventually getting to be equal both the force that causes the aceleration and the force of friction reaching the terminal velocity that a parachutist fro example reaches

but on a surface its different:

force of friction=normal force*MU, where mu is a constant

but the problm here is that this means that if you apply to an object a force bigger than this force of friction it will be acelerating for ever(force applied-force of friction)= m*a (f=ma which btw is also proved wrong by relativity)

so in this case terminal velocity is NOT reached

First example, you reach terminal velocity, the downwards force is constant. You are correct.

The second example is theoretical. If we could have infinite power then you would not reach terminal velocity- you are in powered movement, not freefall. There is no terminal velocity in powered movement, rather a final velocity based on the thrust generated and the air and frictional resistances.

Each engine in the car will have a limit to the force it generates which governs top speed. Top speed has nothing to do with terminal velocity, unless you are driving off a rather tall cliff!

[raaaid]

not really if you apply a force of two newtons to a 1 kg car and theres a rolling friction of 1 N applying f=ma you have a constant aceleration of 1 m/s

everybody knows the faster you go the more it takes to acelerate

according what im studying this is just due to wind friction

but I THINK this is also due to rolling friction increasing with velocity which what im studying denies or neglects

edit:

if what i say its true it brings new grounds on driving

you could have more grip if the wheels turn fast enough skidding than gripping since if v affects friction could be posible to make v as high as that dinamic friction gets bigger than static friction

in fact i recall in f1 times when the cars did go all skidding

[Sternjaeger II]

raaaid do you have a job?

[GraveyardJimmy]

Originally Posted by raaaid

not really if you apply a force of two newtons to a 1 kg car and theres a rolling friction of 1 N applying f=ma you have a constant aceleration of 1 m/s

everybody knows the faster you go the more it takes to acelerate

according what im studying this is just due to wind friction

but I THINK this is also due to rolling friction increasing with velocity which what im studying denies or neglects

Yes, my point is once you reach a high enough velocity wind resistance (or drag) it requires far too much force to move due to resistance increasing with the square of velocity. Therefore acceleration cannot remain constant due to this resistance.

Power required to overcome is:

P= 1/2 p v^3 A C .

Therefore (ignoring constants) power to overcome increases in relation to the cube of velocity, which is not negligible and is the major problem.

[raaaid]

and what would happen if you had a road in the moon

could a 50 horse power car amke the moon rover reach 30000 km/hour taking into account the terminal velocity thing only happens for fluid friction and nor for road friction?

nope i dont have a job now ususally i teach english to kids

[bongodriver]

Poor kids.

[SEE]

Raaid you are posing questions that a lot of kids ask when taught Newtons Laws and formulae such as F=MA. eg, brighter kids will ask - "so, in the void of space, where there is no air or friction why can't a space ship reach the speed of light?" and we end up with all sorts of difficult concepts such as 'uniform acceleration in a straight line', etc, etc........at which point kids either decide to study and take exams in something more easily understood......

And, amid this you have the laws of 'conservation of energy' and Friction has to obey this law regards the energy input and useful energy out. E.g, a car accelerating will create more internal/external friction, more heat energy, probably more sound, and the useful energy is ever diminishing.

[raaaid]

oh havent you noticed my patience? you need that to deal with kids

i never get annoyed however much attacked

i have a degree in english filology but really what capacitates me for that is my inherited patience