Q. Why does soda bubble after a container of it is opened? (Published 1981) (2024)

A. Soda water, like other carbonated beverages, contains carbon dioxide that has dissolved under pressure. When the pressure is released by opening the soda container, the liquid cannot hold as much carbon dioxide, so the excess bubbles out of the solution.

If the soda is left open, additional carbon dioxide will slowly escape into the air. Under warm conditions, the carbon dioxide leaves the solution faster.

Q. Why do the stems in some plants bend toward the sun?

A. Phototropism, or growth toward the light, is one response of plants to light. Usually a straight stalk does not bend toward the light, but growth at the tip will be faster on the dark side, so the new growth will point toward the light. There is an adaptive advantage for a positive phototropic response, since green plants require light to survive. Negative curvature, growth away from the light, can occur in some plants; some vines, for example, find a tree to climb by growing toward the dark, then turn upward when they have found it.

Q. Why do some people bruise easily, and what can be done to prevent or lessen the problem?

A. Bruising easily is often caused by capillary fragility - the tiny blood vessels rupture at a comparatively light blow. But different factors can account for the fragility. Some people may have inherently weak capillaries. Certain drugs, such as anticoagulants, may make the capillaries more fragile or slower to heal.