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Calculation of G Force

  1. Sep 9, 2005 #1

    I'm hoping someone can provide me with a formula to calculate the amount of G Force experienced when decelerating, based on this information :

    A 250cc International Superkart is travelling at 250km/h and is approaching a tight corner than can be taken at a maximum of 80km/h. The driver leaves the braking to the last possible moment, and decelerates from 250km/h to 80km/h in a distance of 80m (whilst in a straight line).

    How many G's has the Superkart and driver experienced ?

    Thanks, Chris.
  2. jcsd
  3. Sep 9, 2005 #2


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    It's pretty straight forward if you neglect friction and wind resistance, etc...

    Note: 250 km/hr = 69.4 m/sec and 80 km/hr = 22.2 m/s

    [tex]V^2 = {V_o}^2 + 2*a* \Delta X[/tex]

    [tex](22.2 \frac{m}{sec})^2 = (69.4 \frac{m}{sec})^2 + 2 a (80 m)[/tex]

    [tex]-4323.5 \frac{m^2}{sec^2} = 160a m[/tex]

    [tex]a = -27.02 \frac{m}{sec^2}[/tex]

    [tex]g's = \frac{a}{9.81 \frac{m}{sec^2}}[/tex]

    [tex]g's = -2.75 [/tex]

    I really hope this wasn't homework. If it was, you got a freebie.
    Last edited: Sep 9, 2005
  4. Sep 9, 2005 #3

    Thanks for that !!

    No, it wasn't homework of any sort ....... unfortunately I'm not studying Physics at all.

    I must look into that formula so that I understand the parameters used and their relationship.

    The speed into metres per second was obvious anyway, but I probably lack the basics to understand and agree with the rest of it. I can see that 4816.3 - 492.84 = 4323.52.

    I wouldn't have thought friction and wind resistance would have been a factor in G force ....... ?

    -2.75 G's ....... my guess before reading the answer was between 2 to 2.5 G's, based on what I've heard for a Formula One car ........

    Once again, thanks for taking the time to reply !! :smile:
  5. Oct 16, 2007 #4

    I'm new on this forum so hello to everyone.

    I'm attempting to monitor the G Force in a vehicle whiles it's driving, does anyone have any ideas?

    All I have is the speed of the vehicle, would this be enough to measure the G Force?

  6. Oct 16, 2007 #5

    Shooting Star

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    No. If the vehicle is moving in a st line with constant speed, there is no g force due to motion of the vehicle.

    You have to know the acceleration. If you are moving with a constant speed on a circular track, then you have to know the radius of the track and the speed.
  7. Oct 16, 2007 #6
    But obviously the vehicle needs to go from 0mph to (say) 90mph,

    Obviously any variation in speed will result in G Force?? Is this correct? Let's say for arguement sake, it's in s straight line?

    How would I work out a running G Force? i.e. Like the one on F1 (ITV)
  8. Oct 16, 2007 #7
    Lets expand on that.

    If I made a trip from A to B, I would want to know the maximum amount of G Force I went through during this trip?

    Can you Help.

  9. Oct 16, 2007 #8

    Shooting Star

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    The actual g force experienced by the driver would be the magnitude of the vector sum of 'a' backward and g downward, which will be equal to sqrt(a^2+g^2)=2.93g. This g force is at an angle tan-inverse(a/g) to the vertical.
  10. Oct 16, 2007 #9

    Shooting Star

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    Hi Huttojb,

    You need some more parameters to find the accn or the g force. If you know the time 't', and accn is constant and the motion is in a st line, then the accn 'a' is (90-0)/t mph/h.

    If you know the dist, then too you can find the accn if it is constant.

    In practice, the accn is generally not constant. So you would need a detailed dist-time graph; or hang a spring balance in the car to see the effective g force. (Note that the reading on the balance would include the g field of the earth.) The maximum accn would perhaps be when you start and reach a high speed in a few seconds. Or when you slow down by stepping on the brakes very hard.
  11. Oct 16, 2007 #10


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    Do a web search for "accelerometer car", you'll find a few companies that sell these, or do a search for "data acquisition car" for high end systems such as this Motec:

    http://www.motec.com/products/dash/adl2dash.htm [Broken]
    Last edited by a moderator: May 3, 2017
  12. Sep 24, 2010 #11
    I have a Physics problem that I cant Figure out:

    An Aircraft goes from 0 MPH to 85 MPH during its take off run of 800 feet in 10 seconds. The aircrafts take-off weight is 2600 pounds and has 4 people aboard with 40 mounds of bags. What is the G-force experienced by the People on board?

  13. Sep 24, 2010 #12

    Ranger Mike

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    we did a lot of posts on this on MEch engineering forum and other forum here

    Centripetal force- Car making a turn Jun6-10, 06:57 AM

    race car suspension class Jul22-09, 11:03 AM

    see post below in gen pyshics forumn..
    Wider tire giving better traction debate! Old Aug15-09, 04:19 AM
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