physics has nowt to do with it try it yourself find a quiet bit of road. stamp on the brake at 30mph then do it at 60 and i bet you it aint 4 times the distance

Also remember most laws of physics are just someones theory/opinion:rofl:

physics has nowt to do with it try it yourself find a quiet bit of road. stamp on the brake at 30mph then do it at 60 and i bet you it aint 4 times the distance

Although threshold braking is much more effective than stamping and can really shorten your stopping distance

Chris

Kinetic Energy

The energy that a body possesses solely because it is moving.

1/2 mass *velocity * velocity

where

m = mass of the body

v = velocity of the body

You double the speed - Kinetic energy 4 times

Treble the speed - Kinetic energy 9 times original

like i said physics is someones opinion/theory :P

Also dont forget as you decrease speed the kinetic energy dissipates into heat and therfore gets smaller so the force of the brakes slows the car down quicker.And its all imaterial anyway because you are limited by the tyres. Brake technology is far superior to tyre tech and until someone invents grippier tyres your still limited by the 4 bits of rubber on the tarmac hence Physics doesnt apply :P:P:P:P:P:P

I thank you im here all week:rofl:

I thank you im here all week:rofl:

repeatedly

Glad to hear you're in 'logical thinking' mode then :thumbdwn:

thats gotta be 1-0 to me

you know im right :P

The stopping distance will be a function of the deceleration applied. Porsche make some of the few cars that can get 1G+ on the brakes. Kinetic energy will have no bearing on the stopping distance. With brakes and tyres producing 1G deceleration, it is all about momentum which is linear with speed.

Contrary to what the highway code states, the average modern car can manage to lose 70mph in well under 300ft. A modern high performance car will stop in a lot less (the MR2, known for its braking capabilities, can stop from 70 in about half the distance between the 100m junction approach markers, so will lose 70mph in 150ft or so). This equates to 2.9 seconds from 70mph to 0 or a loss of 24mph per second.

Given a speed of 172mph, we will see around 7.2 seconds to stop. Average speed will be approximately 86mph, so distance covered will be 908ft. If his brakes and tyres are only up to MR2 standards.

The problem is that we have a relatively inexperienced driver in an unfamiliar vehicle. At these speeds, this is a recipe for disaster. Braking from high speed is a skill that needs to be learned by incrementally building up the speed and stopping force to understand how the car will respond. At those speeds, minor uneveness in the road will be a major cause of stability loss. The speed itself is no big deal IMO and I may have been at this speed on the road with no drama;) but may not have been in the UK at the time(s).

Although it pains me to say it, taking into account experience and familiarity of the vehicle, the guy probably deserved the sentence he got. Had he been an experienced driver in his own familiar vehicle, I would not endorse such a harsh sentence as I would not regard this as reckless.

Chris

Chris

Kinetic energy will have no bearing on the stopping distance.

The kinetic energy of an object is related to its momentum by the equation:

it is all about momentum which is linear with speed.

Funny - more rewriting of the laws of Physics

arrghh i really hate it when people talk about being trained to drive fast what a load of crap.

Your reaction speed will not change it is what it is!

It is you that's talking c.rap matey. Reaction time consists of 7 major elemets.

Each one can be trained.

These are:

Speed - Increase an athletes speed for faster delivery of your techniques.

Anticipation and Timing - Enhance the performance in delivering your techniques.

Power (Speed + Strength - Increase the amount of energy one has, both mentally and physically.

Durability - the ability to last longer and to stay focused.

Sensitivity - to increase the degree of being sensitive and more responsive

Agility - the ability to be more nimble, active.

Motivation - to energize the function that drives your behaviour

It is you that's talking c.rap matey. Reaction time consists of 7 major elemets.

Each one can be trained.

These are:

Speed - Increase an athletes speed for faster delivery of your techniques.

Anticipation and Timing - Enhance the performance in delivering your techniques.

Power (Speed + Strength - Increase the amount of energy one has, both mentally and physically.

Durability - the ability to last longer and to stay focused.

Sensitivity - to increase the degree of being sensitive and more responsive

Agility - the ability to be more nimble, active.

Motivation - to energize the function that drives your behaviour

Nice one:thumbup: i was looking for that as id been told that a few years ago but couldnt remember it all. Bet your head was hurting after finding all that either that or your a sports scientist:rolleyes: :P

V*V = u*u + 2as

In this case, V = 172mph = 77m/s

u = 0mph

Assuming deceleration of 1g = 10m/s/s

Therefore 77*77 = 2*10*s

Hence s = 296m

ahhh yes but

v + t = e

in this case

v= bored at work

t = too much time

e = nerd mode

lol

V*V = u*u + 2as

In this case, V = 172mph = 77m/s

u = 0mph

Assuming deceleration of 1g = 10m/s/s

Therefore 77*77 = 2*10*s

Hence s = 296m

Therefore 976.8 ft which is considerably shorter than 1650ft for 500m.

Phew now weve got that sorted and re-wrote a few laws of physics:rolleyes: How much fuel do you reckon he was using for the following

1. To accelerate to 172mph (assuming he didnt slow down till he got there)

2. To keep the car at 172mph

3. How far could he have gone at that speed before his car ran out of fuel

Also can we work out

1. How much Tyre wear he shaved of accelerating (assuming it was a 4wd Porsche so no wheel spin)

2. How much Tyre wear whilst at 172mph.

3. Theoretically how far could he have travelled before the Tyres reached the 1.6mm legal limit and he had to stop at kwik fit (assuming theoretially he wouldnt run out of fuel)

Once we have solved these i reckon we move onto Proving Einsteins Theory of Relativity

:rolleyes: :rolleyes: :rolleyes: :rofl: :rofl: :P :P :P :P :P :P

Hmmm, you tried a search engine - you nutter :P

See you're still 'on-one'

Nice one:thumbup: i was looking for that as id been told that a few years ago but couldnt remember it all. Bet your head was hurting after finding all that either that or your a sports scientist:rolleyes: :P

No. Just a PE Teacher

No. Just a PE Teacher

It is rumoured

It is rumoured

Cheeky Sod!! :rofl:

The kinetic energy of an object is related to its momentum by the equation:

Obviously the kinetic energy of an object will depend on its momentum and is directly related to it, but for the purposes of calculating stopping distance this is irrelevant.

You seem to be under the mis apprehension that the stopping distance will be linearly proportional to the kinetic energy (ie that stopping distance suares as speed goes up). As anyone with O level physics knows, kinetic energy squares with speed, however, momentum does not. Momentum (the force exerted by the object) is a result of mass x velocity. Now we know the acceleration is going to be a constant 1G or thereabouts, the mass is going to be fixed and therefore the force is going to be fixed (from Force = Mass x Acceleration), acceleration being the change in velocity, which is the crux of the matter.

The only way stopping distance will be affected by kinetic energy is if the braking system is unable to cope with the heat (which will near enough square with speed) and begin to fade. However, we are talking about one stop on a car that will stop at forces greater than 1G and not suffer fade.

Funny - more rewriting of the laws of Physics

Again, although related to kinetic energy, momentum does not square with speed, merely multiplies by speed, so is a linear relationship as I originally stated. Kinetic Energy = Mass x Velocity Squared / 2 x the force of gravity, so does square with speed, and is said to be an exponential relationship, which although true, will have no bearing on the stopping distance in this case.

Kinetic energy content is abstract to the system as the known constant acceleration regardless of speed proves. The Acceleration is fixed by the amount of force the tyres can exert on the road and the force the brakes can transmit to the tyres. This is a linear relationship. If it were down to kinetic energy, the stopping distances would of course square with speed, however, observation (and simple mathematics) proves they do not. Keep it simple.

Chris

Funny that - cos the table at the bottom of this page

Motor bikes - braking distance specifically - must be wrong then

UK Speedtrap Guide. radar detector comparison, compare radar detector, gatso, speeding, speedtrap, gatso camera, blinder, uk speed trap, speed trap uk

30 mph 45 feet

50 mph 125 feet

70 mph 245 feet

So lets take 30mph and 'midway between 50 and 70 mph figures' to arrive at 60 mph

30 mph 45 feet

60 mph 185 feet

So, the speed has doubled and the distance has quadrupled

Keep it simple indeed

Funny that - cos the table at the bottom of this page

Motor bikes - braking distance specifically - must be wrong then

UK Speedtrap Guide. radar detector comparison, compare radar detector, gatso, speeding, speedtrap, gatso camera, blinder, uk speed trap, speed trap uk

30 mph 45 feet

50 mph 125 feet

70 mph 245 feet

So lets take 30mph and 'midway between 50 and 70 mph figures' to arrive at 60 mph

30 mph 45 feet

60 mph 185 feet

So, the speed has doubled and the distance has quadrupled

Keep it simple indeed

Why should the table be wrong? It ties up exactly with how I would calculate the distances. The relationship of speed to stopping distance is linear multiplication.

It really is simple. For example, lets reckon our boy can stop at a rate of 22mph per second per second. From 172mph, he will lose his speed at that rate in 172/22 = 7.81s As the speed loss is linear, his velocity will be reducing in a linear way, his average speed here will have been 172 / 2 = 86mph. 86 x 7.81s = 985ft.

Now half his speed to 86mph. He now takes 3.9s to stop. His average speed is now 43mph he now stops in 245ft.

So if he doubles his speed, he takes 4 times the distance to stop. There are no squares of anything to contemplate, no influence of kinetic energy, it is all just simple and straightforward velocity / time / acceleration / distance stuff.

Look at it another way. If our boy has a fat passenger on board, he can still stop at over 1G. The brakes and tyres will have to transmit greater force, the car will be pressed against the road more by way of compensation. The passenger will however add mass, which will add to the vehicles kinetic energy, but will not add to the stopping distance as the distance is still a product of the acceleration and time. KE is simply not relevant in this case.

Where relationships to factors squared comes in is with high speeds and air resistance. Try rolling off the throttle at 172mph without braking and see how quick your speed comes down. Trust me it is surprising the first time. I clutched in because I thought the engine was about to seize:eek:

This will of course help our boy slow down quicker and he could possibly take under 900ft to stop.

Chris

So if he doubles his speed, he takes 4 times the distance to stop.

Which is exactly what I was saying

Others (previously in the post) weren't, mind :(

Which is exactly what I was saying

Others (previously in the post) weren't, mind :(

Ahh think I see where you are getting KE into the equation now. KE does indeed quadruple if speed doubles. Of course this is a result of KE being a speed multiplied commodity in the same way stopping distance is. However, the stopping distance is not dependent on KE as altering mass (and thus KE) will make no difference to actual acceleration in theory. Just a coincidence that both KE and stopping distance increase with speed by the same proportions if mass remains constant.

If that makes sense?

Chris

Ahh think I see where you are getting KE into the equation now. KE does indeed quadruple if speed doubles. Of course this is a result of KE being a speed multiplied commodity in the same way stopping distance is. However, the stopping distance is not dependent on KE as altering mass (and thus KE) will make no difference to actual acceleration in theory. Just a coincidence that both KE and stopping distance increase with speed by the same proportions if mass remains constant.

If that makes sense?

Chris

TBH - am too far gone, so No

Expect you are / have been too at some point :P

I tell you what - we'll agree to sort of agree - we got very similar results in the end (despite you trying to baffle me with a trace of waffle - I think you been writing too many reports ).

BTW Chris - just what is it you're on.

Want some - must be pretty fine stuff from your very last post :thumbup:

Ace.

of course there is a way he could stop quicker using the same tyre/brake combo and without increasing the co-efficient of friction of both...

he hits a feckin' wall........

Mark