Definition. What is GForce

[Flat Eric]

My understanding of G force is that it represents force exerted by change of speed over a period of time

But what does one unit represent.

How can I work out the measure what gforces are exerted on my car.

[Matt Seabrook]

Get a G meter

[cidersurfer]

Is G the same as g? If it is, it's the rate of change of velocity over time. ie Acceleration. For gravity g=9.81metres/second/second. Since Acceleration is a vector quantity it involves changes of speed, changes of direction or both. Where acceleration is in a direction opposite to it's velocity, acceleration is called decelleration!

[Flat Eric]

Granted, that will give me the resulting G-force figure, but it does not tell me what figure represents.

I want to understand what the gadget does and how it does it, and what does figure actually mean.

(reminds me of hitch hikers guild to galaxy - the answer is 42.)

[peterg]

Very simply for your purposes g = 32ft/sec so that's why for for hillclimbs they put a timer 64ft from the start, if you get there in 2 seconds you've accelerated at 1g  

[adhawkins]

Is G the same as g?

I think G is the unit. 1 G is equal to the earth's gravitational pull (possibly).

Andy

[Flat Eric]

cidersurfer - yes that is what I had in mind.

How do I apply that to my car.

ie if I am driving a 70mph, brake and it takes 2 seconds to reduce speed to 20mph. distance covered to acheive 15m(?)

[cidersurfer]

Hang on. I think we can use Newtons laws for straight line braking, it's when cornering too that things get complicated. If straight line;

v=u+at

v=initial velocity in metres per second

u=initial velocity in metres per second

t=time in seconds

a=acceleration in metres/second/second

so a=(v-u)/t

a=(8.9-31.3)/2

a= -11.2m/s/s or -1.14g

this would happen in a distance (s in metres) of

s=ut+0.5at^2

s=(31.3*2)+(0.5*-11.2*(2^2))=40.4m

edited to add 1m/s=2.23693629mph according to Google

[pete g]

flat

is this why you wear out your eric,s so quickly

[Flat Eric]

cidersurfer, at work at moment, so will read what you said properly on train home this evening. Thanks

...

is this why you wear out your eric,s so quickly

Yes Pete, some questions need a bit of pacing, to help me think about them.

[cidersurfer]

I hope I'm right and some GCSE physics pupil isn't going to put me straight now, it's 21 years since 'o' level physics!

[worldwidewebs]

I think G is the unit. 1 G is equal to the earth's gravitational pull (possibly)

G is the gravitational constant as stated in Newton's Law of Gravity: "the force of attraction between two bodies is proportional to the product of their masses and inversly proprtional to the square of the distance between them". It's value (on earth) is 6.6742 X 10(-11) Nm(2)/kg(2) (can't do "powers" on here, sorry...) Although still generally applicable now, it has been replaced by Eistein's Theory of Relativity...

g is the acceleration due to gravity and is directly proportional to the G between the two bodies. For falling bodies at or very near the surface of the gravitating body, g can be calculated as g = GM/R(2) where R is the radius of the gravitating body and M is it's mass. The exact value of g on earth depends on location as it's not a perfect sphere...

HTH

Andy

[karlos]

I bought one of these.  Great gadget and a bargain price, it comes with a cigerette lighter plug, but I'm sure its easy to mod and fit to the westy somehow

[Mat Jackson]

To answer the original question, a G-force of 1 G means that it is the equivalent force exerted by gravity on the same body.  (This is the little g not the big G)

To acheive this you need to accelerate (or decelerate) at a rate of 9.81m/s^2.

So if you decelerate from 70mph to 20mph in 2 seconds, this is the same as 31.81m/s to 9.09m/s over 2 seconds.

This equates to 11.36 m/s^2, which is just over 1 g.

Hope that helps!!

BTW for cornering you can use the equation a=V^2/r to calculate the centripetasl force and thus the G.

V = velocity in m/s

r = coner radius in m

a= accn in m/s^2

Any suggestins for realistic r values compared to speed?

[neilwillis]

Bert Jones's diary had a very in depth account of how to measure G Force - the technical term was corner weighting!

I understand it involved the use of catapults and various other highly technical stuff like copious quantities of Stella.

Whatever happened to Burt Jones?