Don't let COVID get the better of you 6 (drop small objects)

Let's take a look!

What type of experiment is this?

Experimental procedure and explanation:

• The experiment uses large balls (60 mm in diameter) and small balls (6 mm in diameter), both made of Styrofoam and possessing approximately the same density, and a fine powdery material made of Styrofoam, named snow powder.
• To begin with, both large and small balls are dropped at the same time. The larger balls fall faster.
• This experiment is the same as the previous Large ball and small ball 2 (same density) experiment. If we compare a large ball with a smaller one of approximately the same density, the larger one will fall faster.
• This may be attributed to the nature of air resistance and gravity. The magnitude of air resistance depends on the shape, size, and velocity of the object. Because the magnitude of air resistance is approximately proportional to the area subjected to flow (frontal projected area), it is proportional to the approximate square of the size (length) of the object (for example, if the size is twice as large, the air resistance is approximately four times as great).
• On the other hand, the magnitude of gravity acting on an object of uniform density is proportional to the cube of the object's size (diameter for a sphere ) (for example, if the size is twice as large, the magnitude of gravity is approximately eight times as great). In other words, as the object increases in size, gravity increases greatly.  Further, the gravity becomes more significant than the increase in air resistance. Therefore, for objects of equal density, larger objects fall faster and smaller objects fall more slowly.
• Next, compared to small balls, the small snow powder falls more slowly. This is confirmed by the fact that the finer particles of snow powder are the last to fall.
• This experimental video was produced with the support of JSPS Grant-in-Aid for Scientific Research 18K03956.

[Attention]	We came up with the idea for this experiment because we were curious about the examples of dropping "small stones" or "small objects" that we occasionally saw in high school physics textbooks. What we mean is that, the smaller the stone, the more susceptible it is to aerodynamic drag, which contradicts the assumption that aerodynamic drag should be ignored. For the same density, the effect of aerodynamic drag on an infinitely small object (point mass) will be infinitely large. Dropping "large stones" is dangerous. Indeed, if the size is very small, it makes little difference whether the fall distance is measured from the object's center of gravity or from the object's lowest point. However, it is necessary to understand that if the density is the same, the " smaller" the object , the greater the effect of aerodynamic drag. This is confirmed by the fact that drizzle falls more slowly than large raindrops.
[Keywords]	Drag, aerodynamic drag
[Related items]	Large ball and small ball 2 (same density) , Large Ball and Small Ball
[Reference]	Ryozo Ishiwata, "Illustrated Fluid Dynamics Trivia", Natsume Publishing, P72-75.

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