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Speed on ice

  1. Jan 9, 2010 #1
    If a car is traveling at 30mph on concrete and hits a 1mile patch of solid ice what speed would it be traveling at on the ice
  2. jcsd
  3. Jan 9, 2010 #2


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    Staff: Mentor

    Is this homework? What do you think the answer is?
  4. Jan 9, 2010 #3
    Not homework just an idiot in Texas and I think you travel faster but maybe it's adrenaline
  5. Jan 9, 2010 #4
    Not homework just an 47 year old idiot in Texas and I think you travel faster but maybe it's adrenaline
  6. Jan 9, 2010 #5


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    Staff: Mentor

    Whether you assume much less friction or even no friction at all, there is no change in speed when you get to the ice.
  7. Jan 10, 2010 #6


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    Gold Member

    Actually, there is a deceleration, assuming that you don't have 30 mph or higher tailwind. Even with no friction from the ice (which isn't possible), aerodynamic drag will slow you down.

    edit: Hang on a sec... Conkie didn't say whether he stays on the gas, comes off of it and coasts, or hits the brakes. My answer was based upon closing the throttle and/or braking.
  8. Jan 10, 2010 #7
    It's the "oh shiiiiii- I can't stop if I wanted to" that makes you feel as though you are going faster.

    On the ice you are are most likely going marginally slower regardless of what you do. You are unlikely to accelerate (unless you are goign down hill) as you can't put down any power (wheels just spin). You still have drag and a moderate amount of rollign resistance slowing you.
  9. Jan 10, 2010 #8
    The extra "speed" sensation is actually just the adrenaline rush when you see the world spinning by, left to right, as you do horizontal cartwheels down the highway.
    Bob S
  10. Jan 10, 2010 #9
    I know you're saying to yourself, "this thread needs more equations." So here we go.

    You can approach the car from an energy standpoint were the kinetic energy of the car (KE) is

    [tex]KE =\frac{1}{2}m\: v^{2}[/tex]

    (m=mass, v=velocity)

    Unless you are adding energy by some means, which you could by stepping on the gas or with a tail wind, you cannot gain energy and therefore cannot increase in speed. In reality there will be external forces acting against the car due to friction (though ice is slippery, there will still be some friction) and aerodynamic drag. These forces will decelerate the car according to Newton's second law:


    (F=total force, a=acceleration)
  11. Jan 11, 2010 #10
    If the gas pedal were depressed so as to enter the ice patch at a constant velocity (no acceleration), the wind friction from just about every vehicle more streamlined than a milk truck would not be enough to overcome the slight friction of the tires on "solid ice" as mentioned in the OP. As a result, the vehicle would continue with the same velocity.

    But if we change the conditions and it becomes wet ice, all bets are off. Very slick stuff, wet ice. While ice on ice is 0.1, that's regular ice. That of teflon or steel on teflon is 0.04, while rubber on wet ice is just 0.05. to 0.1, depending on the type of rubber.

    http://www.ameslab.gov/final/News/2008rel/Nanocoatings.html" [Broken]is about half that of teflon.
    Last edited by a moderator: May 4, 2017
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