They are all made of the same length of wire, some are just formed into smaller circles. Wanted to make sure they all had the same chance to sink or float. I used a big, flat book to squish each circle as flat as possible. Because I made them by hand, they all varied My middle sizes wereĪround 30, 40 and 45 to 50 mm. ![]() The smallest was 18 to 20 mm across (around 0.75 inch). I tested fiveĭifferent circle sizes, and tested each circle size 12 times.Ĭomplete circle I could make was around 55 to 60 mm across (around 2 inches). I need to test each size many times, and I also But if some small circles float, and some large circles How many pieces do I need? I could test two groups - smallĪnd large circles. Larger and smaller surface areas, I formed the wire into flat circles ofĭifferent diameters. So to make sure that my fake water striders are all the same mass, I cut the wire into pieces of the same length: 20 centimeters (7.9 inches). This wire is so light that my digital scale can’t even measure it. I started with a spool of wire that is 0.25 millimeter (0.01 inch) thick. Just a tray of water, thin wire and a way to measure it. Larger surface area will float more often than objects of the same mass with a Over an increased area helps things to float. If this is how water striders manage their They way, the water strider floats along on the surface. That way, each leg exerts less pressure on the water and fails to break through Maybe this increased area lets them spread their weight out. Those legs are spread wideĪcross the water. One way to achieve both of these goals is to ![]() Little pressure on the water as possible. To take advantage of buoyancy, the striders would have to be putting down as Tension, all they need to do is not break the surface of the water molecules. Taking advantage of surface tension and buoyancy. To walk across water, water striders could be If the object is exerting more pressure down, If there’s more pressure up from the water than there is down fromĪn object, an object will float. Molecules take up space and exert pressure upward, forcing up anything that is This is the upwardįorce that a fluid exerts toward something being pressed against it. Molecules acting somewhat like a very thin skin that holds the droplet together - surface tension. ![]() Then, a single water droplet will form with its outer layer of water These molecules resist anything that tries to break Instead, they end up attaching to the water molecules next to them, holding on even tighter. Where these molecules meet air, the exposed water moleculesĬan’t attach to any more molecules in front of them - there’s air there. Water molecules are attracted to each other. ![]() Spill water onto a plastic table, and it willįorm droplets - tiny balls of water. But first, I need to know a little bit about Water striders, er, stride, I have to come up with an experiment. Light, but that’s not everything, either. How do they do it? They’re very small, but that’s not it. But little insects called water striders can skim right across the water’s surface. Splash through a puddle and you get your feet You can repeat the steps here and compare your results - or use this as inspiration to design your own experiment. This article is one of a series of Experiments meant to teach students about how science is done, from generating a hypothesis to designing an experiment to analyzing the results with statistics.
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