Sail and Fan

I have been asked the following several times by students of mine... Can a sailboat use a fan to make it sail forward? The answer is no, so why not? Because if you have two forces acting equally on each other, then you are going nowhere. The 2 forces, fan and sail, cancel each other out.

If you use the sail only via the wind, then of course you will sail forward. If you use the fan only against the air you get a fan boat and you move forward, stick the fan blade in the water like a propeller in the denser air called water and you have even more density to push against and again you move forward.

So, it's obvious use sail only or motor only with a fan in the air or propeller in the water to move forward.

Mark Rober talks about this in his video "Testing if you can blow your own sail (see video below)." He also talks about the density of the air that also plays into a sailboat sailing and other affects that are quite interesting.

In addition, Mark points out the importance air density, known as air pressure... On ground there is more air pressure because there are more air molecules, higher up like on the top of Mt Everest, there is much less air pressure, less air molecules. Air molecules weigh more down low than higher up. Gravity is pulling on the air molecules. A helium ballon will rise because its lighter than the air molecules around it. Thus, a sailboat will sail better with more air pressure versus less, but for us sailors the air pressure is always good as we mostly sail at sea level or on lakes that are higher up inland but still have more than enough air pressure.

Mark Rober full video is super interesting, so of course watch the full video below. He makes kits that you can buy to experiment on varies scientific and engineering topics. Well worth the cost for kids and the young at heart. Click this link to visit his website to purchase.

Watch the air pressure topic at the 3 minute and 8 second mark.

Watch just the fan and sail experiment at 5 minutes and 42 second mark.

The whole video is interesting to watch and learn from.