Every child plays with and tests gravity. It is what they do at the age of one when they drop stuff off the table. First they drop it to see what will happen. Next they drop it to see if they can repeat their primary results. For a parent, of course, this is less fun, but such is parenting. All kids are natural scientists exploring how the world works. Even at this point it is possible to tell your child that the item falls, because the earth is pulling on it and this is called gravity. Or you could be more specific and say that the dropped item and earth pull each other, but as earth is quite a bit bigger, things fall towards it and not the other way around. Now, at first, this will mean nothing to the child, but as they grow up hearing it, it will be their explanation of what is happening.
This week we studied gravity and air resistance in a more thorough way as well. Air resistance is a force that slows down movement through the air. It is a related concept to friction, which we test here. In this experiment we first collected stuff. My stuff was a coin and a feather. Her stuff was a hat, some stickers, a play coin, a card, Minni mouse and the baby’s toy giraffe. First we did my test. I picked up the feather and coin and asked her to climb onto a chair. Then I asked her which she thought would drop faster (hypothesis). She thought that the coin would drop faster. Then she dropped them and confirmed her hypothesis. The feather was slower and the coin was considerably faster. Then she dropped the other stuff always two at a time to see which was faster. We changed the order to compare each item to every other item. The feather was slowest, then the stickers, postcard and play coin in that order. For the rest there was no discernible difference.
Then I showed her this clip of Brian Cox visiting the world’s biggest vacuum on Youtube, or more precisely I showed her the part with the bowling ball and feathers dropping first with air resistance. Before they fell down I asked her which she thought would drop faster. She thought the ball would drop faster. It did. Then I moved onto the next bit, but before I showed her I told her that now all the air has been removed from the chamber and it is a vacuum, like it would be in space, I asked which would drop faster now. She knows me pretty well and thought the feathers would. A pretty good guess. We then watched the bit and saw that they dropped at the same time. I explained that in a vacuum they both are drawn towards earth at the same speed as only gravity is affecting them. When there is air present, the air molecules bombard both and the one with more stuff in it, more mass, drops faster as it is less affected by air resistance.
Now, of course, the picture is slightly more complex as gravity does pull harder on items with more mass, because there is more tuo pull on. This is why liquids always find their way below gases. But I’ll leave that discussion for when we study liquids.
Finally we did an experiment designed to minimise air resistance. We took a larger coin and I ripped a small bit of paper that fits on the coin. First we dropped them separately. As expected the coin was much faster. Then I put the piece of paper on the coin and dropped them together and they fell exactly as fast. The coin took care of the air resistance so the piece of paper was unaffected by it, so it went just as fast. Daughter tried to do this as well, but for this she was a bit young. The paper stuck to her finger or she dropped them at an angle in which case the coin no longer protects the paper from air resistance, so we will try this again at a later date.
If you try these experiments at home and your child asks questions, please let me know what types of questions they ask in the comment section so I can further develop these instructions. If you have questions about these experiments or instructions, leave me a comment and I will answer and also improve these instructions. Also, please remember like and share if you find this useful.
Copyright text and images: Satu Korhonen. You are free to try these experiments out, use them in your teaching. But instead of copying the text or images, link back to this page.