Gravity-Powered Sorting Machine
Have you ever used a coin-sorting machine to separate pennies, nickels, dimes, and quarters? When you need to separate things that are all mixed together, using a machine can be much faster than picking them apart by hand. In this project you will build a machine that can automatically separate two different size marbles, powered by nothing but gravity.
This activity is not appropriate for use as a science fair project. Good science fair projects have a stronger focus on controlling variables, taking accurate measurements, and analyzing data. To find a science fair project that is just right for you, browse our library of over 1,200 Science Fair Project Ideas or use the Topic Selection Wizard to get a personalized project recommendation.
Sorting machines are used in many different applications, but they all have something in common. They automate a task that would be very difficult or even impossible to do by hand. It might not be that difficult to sort a pocketful of coins manually, but what if you worked at a bank and had to sort thousands of coins? It would be nice to have a machine to do it! Mining is another example. Early miners would use a manual process called panning to separate gold nuggets from dirt and sand in a pan. Today, huge industrial machines are used to separate valuable gems and minerals from other rocks and dirt. Single-stream recycling facilities have machines that can automatically separate paper, plastic, and metal objects-meaning you can just dump all your recyclables into one bin at home, without sorting them yourself!
How exactly do machines separate all these different materials? They make use of the fact that different objects materials have different properties. For example, some materials are magnetic and some are not, so you can use magnets to separate magnetic and non-magnetic materials. Materials have different densities – meaning some will float in water and some will sink. Some will be easily blown away by a strong puff of air, while others are heavy enough to stay put. Objects have many different sizes and shapes. Some might have smooth, round shapes that let them roll easily (like a ball) and others might have irregular or flat shapes that make them get stuck easily (like a flat piece of cardboard). Smaller objects can fall through holes in a grate while larger objects get stuck on top of it. In this project you will make use of that last point to separate marbles with two different diameters.
Note: this is an engineering design project, so there is not an exact list of materials required to do the project. The list below is a recommendation, but you can substitute other materials.
Observations and Results
It is unlikely that you will build a machine that works perfectly on the first try. In particular, some of the smaller marbles might roll too quickly across the grate while staying on the flat side of a popsicle stick, and never fall through one of the holes, so they wind up in the wrong cup. There are multiple ways you could fix this. You can make the grate longer, to increase the odds that the small marbles will fall through a hole. You can tilt the popsicle sticks or put them on edge so the “flat” sides are not sitting horizontally, so the smaller marbles will always roll down towards the holes. You can put other popsicle stick pieces perpendicular to the rest of the grate to serve as obstacles, causing the marbles to bounce around as they roll down – again, increasing the odds that the small ones will fall through the holes. Once you improve your grate, you should be able to build a machine that can perfectly sort the large and small marbles. It can also help if you pour the marbles into the machine slowly instead of dumping them in all at once.
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Ben Finio, PhD, Science Buddies
Science Buddies |
Gravity, mechanical design, material properties
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