TEXTO PARA AS QUESTÃO

I knew TikTok existed, but | didn't fully understand what it was until a few months ago. |! also realized that something radical, yet largely invisible, is happening on the internet — with implications we still don't understand.

When I was growing up, I took it for granted that the people who became famous enough to be listened to by a crowd had worked hard for that accolade and generally operated with the support of an institution or an established industry.

The idea that I, as a teenager in my bedroom, might suddenly communicate with 100,000 people or more, would have seemed bizarre.

Today's kids no longer see life in these hierarchical and institutional terms. Yes, their physical worlds are often constrained by parental controls, a lack of access to the outdoors and insane over-scheduling.

But despite that (or, more accurately, in reaction to that), they see the internet as a constantly evolving frontier, where it is still possible for a bold and lucky pioneer to grab some land or find a voice. Most voices on the internet never travel beyond a relatively small network, and much of the content that goes viral on platforms such as TikTok, YouTube or Instagram does so because of unseen institutions at work (for example, a public relations team aiming to boost a celebrity's profile).

Fame can suddenly appear — and then just as suddenly be taken away again, because the audience gets bored, the platform's algorithms change or the cultural trend that a breakout video has tapped into goes out of fashion.

For a teenager, social media can seem like a summer garden at dusk filled with fireflies: spots of lights suddenly flare up and then die down, moving in an unpredictable, capricious display. Is this a bad thing? We will not know for several years.

Financial Times. 5 February 2020. Adaptado.

TEXTO PARA A QUESTÃO

As astronomers gaze into the depths of space, they do so with unease: They don't know precisely what the universe is made of. Surprisingly, no one knows the stars” exact chemical composition: how many carbon, nitrogen and oxygen atoms they have relative to hydrogen, the most common element.

These numbers are crucial, because they affect how stars live and die, what types of planets form and even how readily life might arise on other worlds.

Twenty years ago, astronomers expressed confidence in the numbers they had been working with. Now, not so much. The problem lies not in the far corners of the cosmos, but much closer to home. Astonishingly, scientists don't know exactly what the sun is made of. As a result, they don't know what the other stars are made of, either.

“The sun is a fundamental yardstick,” says Martin Asplund, an astrophysicist at the Max Planck Institute for Astrophysics, in Germany. “When we determine the abundance of a certain element in a star or a galaxy or a gas cloud anywhere in the universe, we use the sun as a reference point.”

The sun's location in the Milky Way also makes it a good representative of the entire galaxy. Most stars reside in giant galaxies like the Milky Way, which makes the sun a touchstone for the entire cosmos.

For nearly a century, astronomers have judged stars normal or not by seeing whether their chemical compositions match the sun's. Most stars near us do; some don't.

Scientific American. 1 July 2020. Adaptado.

Um experimento expôs uma barra de titânio (Ti) pura e ligas desse material com 0,01% de diferentes metais nobres a soluções de ácido sulfúrico em ebulição para entender o efeito anticorrosivo desses metais no titânio. O resultado é mostrado na tabela a seguir:

*Não foi possível medir.