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2nd grade homework concerns

  1. Sep 18, 2013 #1
    My daughter came home with this assignment (see PDF link below) tonight. Am I right to be concerned when they equate power with force, and size with mass? Or am I just over-blowing this for 2nd grade?

    https://dl.dropboxusercontent.com/u/49570443/homework.pdf [Broken]

    I explained to her that push and pull are just opposites of one another; negative and positive forces since she is familiar with negative numbers. Then explained that size has nothing to do with it, rather weight (I did not discuss mass), and explained a bowling ball and soccer ball are the same size yet require different forces to move. Then explained energy as what it takes to move an item from one location to another, while more power is required to get it there faster.

    Is this a preview of what's to come? Maybe this is out of the "common core" curriculum, which doesn't get my hopes up. I'll ask her teacher where she found it.
    Last edited by a moderator: May 6, 2017
  2. jcsd
  3. Sep 18, 2013 #2


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    It's a problem that the words we use in physics can have different meanings in everyday language.

    "The power that makes other things move is called a force". Power here is meant as an influence or an aspect that induces action, and not as energy expended per unit time. Its semantics are difficult, but all it really says is that a force is a force is a force. It makes things move.

    This is not a good worksheet for any grade.
    Kids know about pushing and pulling, and it would confuse them to have these redefined.
    What should be done is to say that a force is a push or pull, and that forces are what make things move that weren't moving before, and what stops things that are moving, and also what changes the directions things are moving in.
  4. Sep 18, 2013 #3
    If second graders are even considering physics, that is a huge step forward. I'm pretty sure I was just learning to add and subtract numbers at that time
  5. Sep 18, 2013 #4


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    also, for ideas of how to talk to second graders about physics, I recommend looking at:

    The simple english wikipedia (good for both young children and those learning english)

    And to try your hand at explaining things as simply as possible, I recommend the "up goer five" text editor
  6. Sep 19, 2013 #5


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    I think you are up in arms about nothing, to be honest. They are simply teaching kids to think physically earlier and trying to do so without using overly difficult concepts and language for a child that age. They aren't equating force with the physics meaning of power, that is the rate of change of energy. They are using power to describe some action that causes an event.

    It's no different than high school teachers teaching their students that the derivative is the slope of a graph, which is a very basic and narrow definition of a derivative. It is just introducing the topic and the concepts will be expanded later, only instead of high school seniors, they are introducing the topic to second graders.
  7. Sep 19, 2013 #6


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    One should explain things as simple as possible but not simpler, to freely cite Einstein.

    One should teach physics correctly on whatever level. Science without an as concise as possible use of terms is no science, and the proper use of concepts is something one has to learn from the very beginning. Of course, you cannot start with formal mathematics, but you should not use wrong notions. I think kids can understand that an exact science like physics needs refined notions and a an uncritical use of everyday words may be misleading.

    Last but not least in an early stage of physics learning, simple experiments done by the kids themselves are the key for both motivation and understanding!
  8. Sep 19, 2013 #7


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    Ditto. When discussing nature and the universe with my 6-year-old, I find it very hard to keep the vocabulary exact. It is often better to twist a bit the meaning of a common work than to introduce new words that are hard to understand.

    I am much more worried by explanations that give agency to inanimate objects.
  9. Sep 19, 2013 #8
    Makes you wonder if it's worth bothering at that level. The only non-intuitive elements (large things aren't always more massive) was completely fudged over, do away with the test and give them some weights to play with.

    I didn't learn the difference between mass and weight until I was 12, and didn't know the difference between weight and density until I was 15. Chalking clearly misleading elementary physics texts up to semantics is the reason for that.

    All you need to do is show a spaceman jumping on the moon, or a lump of wood floating whilst a coin sinks. It's ALL intuitive. Having said that I don't believe my teachers understood the difference below the age of 12.
  10. Sep 19, 2013 #9


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    First off, madengr:
    I think you made a good job trying to help your daughter. It is not the fault of you that that stupid sheet used the energy concept. For very good reasons, physicists weren't interested in that quantity until the 1820s or so, when it dawned upon them that HEAT was related to dissipation of enery, and that therefore, energy was a conserved quantity. Energy is a bit too abstract, I think, at your daughter's age, and understanding pushes and pulls are challenging enough.
    I am glad you caught the really big blooper here, that big objects needs a big force, small objects a small force to move. They even put it as a question to be answered (in)correctly!!
    Yes, we should keep close to the natural intuition of a child, but EVERY child knows what "heavy"/"light" means, and that that has nothing to do with the bigness of the object.

    AND: Since weight is strictly proportional to mass here on earth, it can stand as pseudo-mass without causing too much distortion.
  11. Sep 19, 2013 #10


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    A good example of the heavy/light misconception is the dawn spacecraft. This space probe is the size of a small car (slightly less mass than a Honda civic at launch). The thruster is 90mN. This is about the same force as the weight of 10 paperclips. Over the course of the mission this will accelerate the ship by 10km/s.

    This is a miniscule force. You can literally(by the ancient definition of literally) carry it around in your pocket without really considering it. It is sending a sizable object far into the solar system.

    When you simplify concepts for children you should not make them so simple they are outright lies.

  12. Sep 22, 2013 #11


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    What really bugs me is when you recognise the question has been oversimplified, give the correct answer and they mark you wrong! For example in answer to question 5) suppose she had written...

    "Size doesn't matter. It's the mass of the object that matters."

    I'd feel aggrieved if they had marked that wrong.

    Sadly it happens a lot. I once had a summer job checking that examiners had seen and marked every page of a candidates paper. One question asked the candidates to draw a simple electronic circuit called a bridge rectifier. There are several ways you can draw one of those but as long as the topology is right they are all correct. I noticed the examiner had marked lots of them incorrect when in fact they were electrically correct. I drew this to the attention of the boss but never heard any more.
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