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Homework Help: Car safety experiment

  1. Mar 21, 2003 #1
    Hey there everyone

    I need to do a presentation that shows the danger of having loose objects in the car...using Newton's first law...i'm stuck for ideas, we have to make some experiment like an egg on a trolley or something...does anyone have any ideas?

  2. jcsd
  3. Mar 21, 2003 #2
    Newton's first law goes as follows: An object in motion will tend to stay in motion unless disturbed by an outside force.

    With that in mind, if one is traveling in a car (i.e in motion) at.. oh lets say... 13 m/s (approx. 30 mph), their body *is* traveling at that speed (as are the other loose objects in the car), and for a body with that much momentum (lets say an infant, as a "loose object" that weight 4 Kilograms... that is why they have special car seats) with the momentum of 52 Kg*m/s (mass * velocity = momentum)....

    were to come to a sudden halt in.. oh lets say 0.5 seconds because some guy who just got kicked by an intense relation started rolling down from a hill, rolled into the street...

    the force of impact the infant would have if it was not strapped to its car seat would be the following:

    F= mass * delta velocity/ delta time ("delta" meaning, "change in")

    so the force the infant would extert on a particular object (the "outside force that disturbs the body in motion".-window? and remember newton's third law: for every action there is an equal and opposite reaction. i.e "the wall hits me back as hard as i hit it") if it were to fly out of its baby car seat would be... 104 Newtons.

    Which can do some damage.

    I dont know about an egg in a trolly...

    But you can apply the principles of impulse (force * time= impulse=change in momentum over time) by throwing an egg at a wall (and watching it break) and throwing an egg (at approx the same speed) at a towel (somebody should be holding the towel) and watch it NOT break.

    the "change in time" will be bigger for the egg being thrown at the towel, hence the impulse is smaller. -thus, will likely not break as opposed to having a "small" change in time, which would make the impulse bigger. (the equation explains this)

    umm... if this was not helpful.... i am sure you can find allllllllll sorts of stuff on the net that can help explain this.

    i just punched some stuff into google, and this might be useful, or not.


    good luck.
  4. Mar 21, 2003 #3


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    If the loose object is a rattlesnake the demo is pretty easy. :wink:

  5. Jul 8, 2010 #4
    I once hitched a lift in a lorry carrying over 20 tons of steel bars on a flatbed right behind the cab.
    The driver had never heard of Newton's first law. I guess that's why he took the job.
  6. Jul 8, 2010 #5


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    Gold Member

    My brother-in-law once did just such a demonstration himself. He had a tool-box full of heavy stuff like wrenches, hammers, chisels, etc on the floor of the cab of his pickup and he missed a curve and rolled his truck in the ditch. That toolbox beat the crap out of him. To add to the authenticity, he wasn't wearing his seat-belt (never does!). I'm surprised he's still alive.

    You could do a safer demonstration using a clear plastic enclosure on a cart with an egg and a ball-bearing or a large hex nut or some other dense object inside.
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