Mars is the fourth planet from the Sun — a dusty, cold, desert world with a very thin atmosphere. Mars is also a dynamic planet with seasons, polar ice caps, canyons, extinct volcanoes, and evidence that it was even more active in the past.

No other planet has captured our collective imagination quite like Mars.

In the late 1800s when people first observed the canal-like features on Mars’ surface, many speculated that an intelligent alien species resided there. This led to numerous stories about Martians, some of whom invade Earth, like in the 1938 radio drama, The War of the Worlds. According to an enduring urban legend, many listeners believed the story to be real news coverage of an invasion, causing widespread panic.

Countless stories since have taken place on Mars or explored the possibilities of its Martian inhabitants. Movies like Total Recall (1990 and 2012) take us to a terraformed Mars and a struggling colony running out of air. A Martian colony and Earth have a prickly relationship in The Expanse television series and novels.

Internet: <www.solarsystem.nasa.gov> (adapted).

In a world where many of us are glued to our smartphones, Dulcie Cowling is something of an anomaly — she has ditched hers. The 36-year-old decided at the end of last year that getting rid of her handset would improve her mental health. So, over Christmas she told her family and friends that she was switching to an old Nokia phone that could only make and receive calls and text messages.

She recalls that one of the pivotal moments that led to her decision was a day at the park with her two boys, aged six and three: “I was on my mobile at a playground with the kids and I looked up and every single parent — there was up to 20 — were looking at their phones, just scrolling away,” she says.

“I thought ‘when did this happen?’. Everyone is missing out on real life. I don’t think you get to your death bed and think you should have spent more time on Twitter, or reading articles online.”

Ms Cowling, who is a creative director at London-based advertising agency Hell Yeah!, adds that the idea to abandon her smartphone had built up during the covid-19 lockdowns.

“I thought about how much of my life is spent looking at the phone and what else could I do. Being constantly connected to lots of services creates a lot of distractions, and is a lot for the brain to process.”

She plans to use the time gained from quitting her smartphone to read and sleep more.

About nine out of 10 people in the UK now own a smartphone, a figure broadly replicated across the developed world. And we are glued to them — one recent study found that the average person spends 4.8 hours a day on their handset.

Yet for a small, but growing number of people, enough is enough.

Alex Dunedin binned his smartphone two years ago. “Culturally we have become addicted to these tools,” says the educational researcher and technology expert. “They are blunting cognition and impeding productivity.”

He has become happier and more productive since he stopped using a smartphone, he says.

Mr Dunedin doesn’t even have an old-fashioned mobile phone or even a landline anymore. He is instead only electronically contactable via emails to his home computer.

“It has improved my life,” he says. “My thoughts are freed up from constantly being cognitively connected to a machine that I need to feed with energy and money. I think that the danger of technologies is that they are emptying our lives.”

Yet, while some worry about how much time they spend on their handset, for millions of others they are a godsend.

“More than ever, access to healthcare, education, social services and often to our friends and family is digital, and the smartphone is an essential lifeline for people,” says a spokesperson for UK mobile network Vodafone.

“We also create resources to help people get the most from their tech, as well as to stay safe when they’re online — that’s hugely important.”

Suzanne Bearne.

The people deciding to ditch their smartphones. Internet: <www.bbc.com> (adapted).

A PETROBRAS responde por cerca de 80% dos combustíveis ofertados no Brasil. Para isso, muito foi investido em infraestrutura, com operações que consomem quase 100 bilhões de reais ao ano, conforme dados de 2021.

O caminho do petróleo do poço até virar combustível no carro das pessoas é longo e complexo. Começa na procura: acertar onde furar e encontrar petróleo exige conhecimento técnico de geólogos e geofísicos e bastante investimento. E, mesmo com um time de experts do mais alto nível, achar petróleo não é certo.

Transportar o petróleo do mar até as refinarias é também uma tarefa complexa, para a qual são utilizados dutos e navios. Em terra, ele é tratado em refinarias, que separam desse óleo as frações de gasolina, diesel e gás de cozinha, entre outros derivados. Os produtos são então disponibilizados às diversas distribuidoras que hoje atendem o mercado brasileiro, responsáveis por fazer chegar cada um deles aos consumidores finais.

Internet: <duvidasgasolina.petrobras.com.br> (com adaptações).

A figura a seguir ilustra um bloco sobre uma barra horizontal de tamanho L, presa por uma corda inextensível, fixada em uma parede, e exercendo sobre a barra uma força tração !$ \vec{T} !$. A barra está também fixada em uma junção com a normal !$ \vec{N} !$ sobre ela. Essas forças que atuam na barra e que junto com o força peso mantêm o sistema em equilíbrio estático estão mostradas na figura, bem como os seus pontos de atuação. As componentes das forças podem ser descritas em um sistema cartesiano bidimensional que contêm todas as forças que atuam na barra.