Questões de Concurso

How things work: 100 scientific explanations

Preservation property has always been important to humans. Historians in the ninth century were the first to record the use of varnish, a protective liquid composed of resins, natural oils, and alcohol, among other ingredients. Furniture makers learned that if they painted coats of the stuff on a piece of furniture or wood floor, it made it impervious to liquids and their damage and shielded it from normal wear and tear. And the makers liked the shine furniture had after it was varnished.

Varnish comes in many formulations. Some are oil based, using linseed or tung oil, while others are water-based. Varnish cures, or dries, on what it’s painted, creating a glossy, clear film on the surface. Some oil-based varnishes can turn to a yellowish color; water-based varieties do not. Wood must be carefully cleaned and sanded before any varnish is applied. Several coats are often required. All varnishes contain resins — terpenes with five-carbon molecules called isoprenes and also include a drying oil or solvent to reduce drying time.

Although furniture and flooors are still the most frequently varnished items, the wooden hulls of boats are also often varnished. Clear nail polish, a type of varnish, can be used for countless small fixes: dab small amounts to keep splintered wood from snagging, prevent ink from running, and stop buttons on clothing or screws on sunglasses from coming loose.

(National Geographic Special Publication “How Things Work” Adapted.)

First study of all Amazon greenhouse gases suggests the

damaged forest is now worsening climate change

The Amazon rainforest is most likely now a net contributor to warming of the planet, according to a first-of-its-kind analysis from more than 30 scientists.

For years, researchers have expressed concern that rising temperatures, drought, and deforestation are reducing the capacity of the world’s largest rainforest to absorb carbon dioxide from the atmosphere, and help offset emissions from fossil-fuel burning. Recent studies have even suggested that some portions of the tropical landscape already may release more carbon than they store.

But the inhaling and exhaling of CO2 is just one way this damp jungle, the most species-rich on Earth, influences the global climate. Activities in the Amazon, both natural and human-caused, can shift the rainforest’s contribution in significant ways, warming the air directly or releasing other greenhouse gases that do.

Yet no team had ever tried to assess the cumulative impact of these processes, even as the region is being rapidly transformed. The research estimates that atmospheric warming from all of these sources combined now appears to swamp the forest’s natural cooling effect.

The damage, however, can still be reversed. Halting global emissions from coal, oil, and natural gas would help restore balance, but curbing Amazon deforestation is a must, along with reducing dam building and increasing efforts to replant trees. Continuing to clear land at current rates appears certain to make warming worse for the entire world.

Internet:<www.nationalgeographic.com> (adapted).