Let’s Build a Simple Wind-Powered Car

Project Overview:
Disappointed by how quick your battery-powered car runs out of charge? Build your very own car that moves purely off wind power - no motor or batteries necessary. Test it against a fan or even just run it outside on a windy day. It's a cool way to see how wind actually turns into motion, which is basically the same idea behind sailboats and wind turbines. 

Materials:

1. A small cardboard base or a recycled container 

2. 4 bottle caps or small wheels

3. 2 wooden skewers or straws 

4. A sheet of cardstock or stiff paper

5. A straw or small dowel 

6. Tape or a hot glue gun (get an adult for the glue gun part!)

7. A fan (for consistent testing indoors)

Instructions:

1. Tape or glue two skewers across the bottom of your car's base so they act as axles

2. Poke a hole through the middle of each bottle cap and stick them onto the ends of the axles as your wheels

3. Cut your cardstock into whatever sail shape you want: a rectangle's easiest, or go with a taller triangle if you prefer so

4. Tape or glue the sail onto your straw or dowel, then mount it standing up in the middle of the car

5. Set the car down on something smooth and flat, sail facing whichever direction the wind or fan is coming from

6. Turn the fan on, or take it outside if there's a steady breeze, and watch what happens

7. Try messing with the size or shape of the sail and test it again to see if it changes how far or fast it goes

Explanation:
Wind is  billions of air molecules physically slamming into whatever's in their path, and every single one of those tiny hits transfers a little bit of force. On your DIY car, the sail catches as many of those hits as possible, which is why a bigger sail works better. More surface area means more molecules have something to crash into at once. All those tiny individual hits from the air add up together into one steady push, and that's what actually moves your car forward. So messing with the size of your sail changes how many molecules it's catching, which is why a bigger sail usually pushes with more force than a small one (though obviously there's a limit before it just gets too heavy). This is the same idea that's been powering actual sailboats for thousands of years!