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Home : 2002 : Feb : 22

    Newton's Third Law
    By Farrah

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    I just finished teaching a unit about Newton's Laws of Motion. To introduce the third law, I hung two styrofoam balls from the ceiling at the same height. I then blew on one of the balls, so that it would hit the other one. We did this a few times, discussing why the second ball moved. (They all wanted to swing the balls.) We talked about air being the force, and what would happen if we changed the speed of the air.

    I then asked them what would happen if I blew in between the balls (they predicted that each ball would move away from the air flow). I then demonstrated that when you blow in between the balls, they will move close to eachother instead of away. This brought on the discussion of other forces, such as air pressure and gravity. (The balls moved together because when I blew the air in between them, the moving air created a low pressure area. The high pressure area all around the ball, caused air to rush in to the low pressure area, taking the balls with it.) My kids really got a kick out of that.

    We also took two marbles and tried to roll them into each other. You can see how the direction changes if you dip the marbles in paint first.

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