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Snowball out of a Car

  1. Nov 15, 2015 #1
    Hi there.

    Hopefully I'm posting this in the correct place. I took a look at the guidelines and decided not to post in the general physics forum as this question does seem homework-like, though it's not exactly homework. Just a general physics question if that's alright. If this is the incorrect place to post this question then please tell me so I'll know not to do so in the future.

    My physics teacher mentioned that if you wanted to throw a snowball at someone in order to hit them with as much force as possible (he said this jokingly and told us not to actually try it out) that you could get inside of a car and throw a snowball out towards your target (such as a person or whatever it may be) as the speed at which the snowball traveled would be equal to the speed at which the car was also traveling.

    For example: I'm inside of a car travelling 50 km/h, and I decide to throw a snowball out of that car towards a tree. The snowball would also be travelling at 50 km/h, and thus it would hit the tree with force proportional to the speed it was traveling at.

    Now our physics teacher didn't explain why this would happen, and I searched on Google for possible answers, but to no avail.

    Could anyone explain the physics behind this? I find the idea interesting and it's been on my mind for the past few days.

    Last edited: Nov 16, 2015
  2. jcsd
  3. Nov 16, 2015 #2
    Huh. Looks like it was moved to general physics anyways.
  4. Nov 16, 2015 #3


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    Staff: Mentor

    Both you and the snowball accelerated with the car relative to the tree. So when you toss the snowball out the window, it is still going at 50 km/h.
  5. Nov 16, 2015 #4
    For the same reason that if you jump out of a moving car you get hurt. If it weren't like that. You could jump out of cars and nothing would happen to you.
  6. Nov 16, 2015 #5


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    Staff Emeritus
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    Homework Helper

    If you want the physics explanation, it's Newton's First Law of Motion:

    "An object either remains at rest or continues to move at a constant velocity, unless acted upon by an external force."

  7. Nov 16, 2015 #6


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    Gold Member

    The speed with which the snowball hits the tree depends on the force and angle towards the tree with which you throw it. For example, your very poorly stated problem does not prohibit a solution where the throw the snowball out of the car at 51mph back towards the tree after you have passed it and it hits the tree at 1mph. OR, you could throw the snowball out of the car at 10mph directly towards an oncoming tree and hit the tree at 60 mph.

    A proper statement (that I think your prof was making) is that you toss the snowball out of the car with zero forward velocity relative to the car but outwards towards the tree.

    It's common to use that kind of poorly stated problem to demonstrate the basics but the fact that it is common does not make it a good idea.
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