In the video below, Dianna Cowern (Physics Girl) shows the interesting thing that happens when the flame of a candle is exposed to falling.
While I understand the need to make the science accessible and fun in a short video, Dianna describes the effects of freefall on the candle flame to be a consequence of “taking away gravity”, and she also says that, “Falling towards the Earth pulled down by gravity, is just like floating out in space with no gravity at all”. Neither of these things is true.
The gravity that we are talking about, is that produced by the Earth. To “take away gravity” or to “have no gravity”, the Earth would have to disappear! What really happens during freefall that gives the candle flame that shape is that the forces that oppose gravity are diminished or nullified. Because this eliminates buoyancy, hot air can no longer rise. This is counterintuitive, and visualizing it is more complicated and difficult to explain in a video, but if you are interested, I wrote a post about it here.
I am fascinated by water striders. These insects are uniquely adapted for their life on the surface of the water. I filmed several of them in a creek. You can’t really see the actual insects very well in the video below, but you can see two things that give away their presence.
The first is that each insect generates two small round shadows and a larger round shadow on the surface of the water. These shadows are created by the way light is altered by the bending of the surface of the water by the strider’s rear (small shadows) and front (large shadow) legs. These insects exploit the surface tension of water to stay afloat coupled with adaptions in the tips of their legs that make the legs water repellent and also help them trap little bubbles of air resulting in high buoyancy.
The second is that these insects use their middle legs as oars generating an explosive movement that propels them forward giving rise to waves that radiate from the strider in a concentric pattern. A multitude of striders in one place can create quite a display of circular waves giving rise to cool interference patterns as shown in the video.
Just before eating my breakfast at a local restaurant, I fancied testing some scientific principles related to pressure and temperature differentials and buoyancy. First, I inserted my straw into the hot coffee and blocked the top of the straw with my finger. In this way I was able to remove the straw with a column of hot coffee inside it leaving the bottom open. Some people claim that this occurs because the gravity pulling down on the column of coffee produces a vacuum inside the straw, and the vacuum sucks the coffee into the straw preventing it from flowing out. This is not true. Like I have explained before, vacuums don’t suck. The pull of gravity tends to create a low pressure area inside the straw, and the push of the atmospheric pressure against the bottom of the column of coffee is enough to counter gravity and keep it inside the straw.
I then proceeded to place the tip of the straw with the coffee inside the cold milk. The hot coffee is less dense than the cold milk. Under the influence of a gravitational field, liquids that are less dense will float on top of liquids that are denser. You can see in the video that, even though the coffee is in direct contact with the milk at the bottom of the straw, the column of coffee inside the straw remains by and large unperturbed (with the exception of some coffee at the coffee-milk interface mixing with the milk due to equilibration of the temperatures of the liquids). Then I did the opposite. I placed a column of milk inside the straw in contact with the coffee. Because the hot coffee is less dense than the milk it starts flowing up the straw almost immediately, while the cold milk that is denser flows in the opposite direction.
After this I ate my breakfast: scrambled eggs with bacon and home fries and blueberry toast (with no butter).