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Um potenciômetro foi construído utilizando-se dois fios resistivos ôhmicos, paralelos, de mesmo comprimento e mesma resistência elétrica. Os fios são tocados por um contato móvel, de resistência desprezível, que desliza perpendicularmente aos fios, tornando todo o conjunto um potenciômetro. Este potenciômetro está ligado a um gerador de 100 V e a um amperímetro, ambos ideais.
Quando o contato móvel do potenciômetro se encontra na posição indicada na figura, o amperímetro indica a passagem de uma corrente elétrica de 5 A.
Individualmente, cada um dos fios resistivos que constituem
o potenciômetro apresenta, entre seus extremos, a resistência elétrica de
A figura mostra uma esfera, de 250 g, em repouso, apoiada sobre uma mola ideal comprimida. Ao ser liberada, a mola transfere 50 J à esfera, que inicia, a partir do repouso e da altura indicada na figura, um movimento vertical para cima.
Desprezando-se a resistência do ar e adotando-se g=10 m/s2
,
a máxima altura que a esfera alcança, em relação à altura de
sua partida, é
De dentro do ônibus, que ainda fazia manobras para estacionar no ponto de parada, o rapaz, atrasado para o encontro com a namorada, a vê indo embora pela calçada. Quando finalmente o ônibus para e o rapaz desce, a distância que o separa da namorada é de 180 m.
Sabendo que a namorada do rapaz se movimenta com velocidade constante de 0,5 m/s e que o rapaz pode correr com velocidade constante de 5 m/s, o tempo mínimo para que ele consiga alcançá-la é de
According to the chart,
An increasing body of evidence suggests that the time we spend on our smartphones is interfering with our sleep, self-esteem, relationships, memory, attention spans, creativity, productivity and problem-solving and decision-making skills. But there is another reason for us to rethink our relationships with our devices. By chronically raising levels of cortisol, the body’s main stress hormone, our phones may be threatening our health and shortening our lives.
If they happened only occasionally, phone-induced cortisol spikes might not matter. But the average American spends four hours a day staring at their smartphone and keeps it within arm’s reach nearly all the time, according to a tracking app called Moment.
“Your cortisol levels are elevated when your phone is in sight or nearby, or when you hear it or even think you hear it,” says David Greenfield, professor of clinical psychiatry at the University of Connecticut School of Medicine and founder of the Center for Internet and Technology Addiction. “It’s a stress response, and it feels unpleasant, and the body’s natural response is to want to check the phone to make the stress go away.”
But while doing so might soothe you for a second, it probably will make things worse in the long run. Any time you check your phone, you’re likely to find something else stressful waiting for you, leading to another spike in cortisol and another craving to check your phone to make your anxiety go away. This cycle, when continuously reinforced, leads to chronically elevated cortisol levels. And chronically elevated cortisol levels have been tied to an increased risk of serious health problems, including depression, obesity, metabolic syndrome, Type 2 diabetes, fertility issues, high blood pressure, heart attack, dementia and stroke.
(Catherine Price. www.nytimes.com, 24.04.2019. Adaptado.)
An increasing body of evidence suggests that the time we spend on our smartphones is interfering with our sleep, self-esteem, relationships, memory, attention spans, creativity, productivity and problem-solving and decision-making skills. But there is another reason for us to rethink our relationships with our devices. By chronically raising levels of cortisol, the body’s main stress hormone, our phones may be threatening our health and shortening our lives.
If they happened only occasionally, phone-induced cortisol spikes might not matter. But the average American spends four hours a day staring at their smartphone and keeps it within arm’s reach nearly all the time, according to a tracking app called Moment.
“Your cortisol levels are elevated when your phone is in sight or nearby, or when you hear it or even think you hear it,” says David Greenfield, professor of clinical psychiatry at the University of Connecticut School of Medicine and founder of the Center for Internet and Technology Addiction. “It’s a stress response, and it feels unpleasant, and the body’s natural response is to want to check the phone to make the stress go away.”
But while doing so might soothe you for a second, it probably will make things worse in the long run. Any time you check your phone, you’re likely to find something else stressful waiting for you, leading to another spike in cortisol and another craving to check your phone to make your anxiety go away. This cycle, when continuously reinforced, leads to chronically elevated cortisol levels. And chronically elevated cortisol levels have been tied to an increased risk of serious health problems, including depression, obesity, metabolic syndrome, Type 2 diabetes, fertility issues, high blood pressure, heart attack, dementia and stroke.
(Catherine Price. www.nytimes.com, 24.04.2019. Adaptado.)
An increasing body of evidence suggests that the time we spend on our smartphones is interfering with our sleep, self-esteem, relationships, memory, attention spans, creativity, productivity and problem-solving and decision-making skills. But there is another reason for us to rethink our relationships with our devices. By chronically raising levels of cortisol, the body’s main stress hormone, our phones may be threatening our health and shortening our lives.
If they happened only occasionally, phone-induced cortisol spikes might not matter. But the average American spends four hours a day staring at their smartphone and keeps it within arm’s reach nearly all the time, according to a tracking app called Moment.
“Your cortisol levels are elevated when your phone is in sight or nearby, or when you hear it or even think you hear it,” says David Greenfield, professor of clinical psychiatry at the University of Connecticut School of Medicine and founder of the Center for Internet and Technology Addiction. “It’s a stress response, and it feels unpleasant, and the body’s natural response is to want to check the phone to make the stress go away.”
But while doing so might soothe you for a second, it probably will make things worse in the long run. Any time you check your phone, you’re likely to find something else stressful waiting for you, leading to another spike in cortisol and another craving to check your phone to make your anxiety go away. This cycle, when continuously reinforced, leads to chronically elevated cortisol levels. And chronically elevated cortisol levels have been tied to an increased risk of serious health problems, including depression, obesity, metabolic syndrome, Type 2 diabetes, fertility issues, high blood pressure, heart attack, dementia and stroke.
(Catherine Price. www.nytimes.com, 24.04.2019. Adaptado.)
No trecho do primeiro parágrafo “But there is another reason for us to rethink our relationships with our devices”, o termo sublinhado introduz uma
An increasing body of evidence suggests that the time we spend on our smartphones is interfering with our sleep, self-esteem, relationships, memory, attention spans, creativity, productivity and problem-solving and decision-making skills. But there is another reason for us to rethink our relationships with our devices. By chronically raising levels of cortisol, the body’s main stress hormone, our phones may be threatening our health and shortening our lives.
If they happened only occasionally, phone-induced cortisol spikes might not matter. But the average American spends four hours a day staring at their smartphone and keeps it within arm’s reach nearly all the time, according to a tracking app called Moment.
“Your cortisol levels are elevated when your phone is in sight or nearby, or when you hear it or even think you hear it,” says David Greenfield, professor of clinical psychiatry at the University of Connecticut School of Medicine and founder of the Center for Internet and Technology Addiction. “It’s a stress response, and it feels unpleasant, and the body’s natural response is to want to check the phone to make the stress go away.”
But while doing so might soothe you for a second, it probably will make things worse in the long run. Any time you check your phone, you’re likely to find something else stressful waiting for you, leading to another spike in cortisol and another craving to check your phone to make your anxiety go away. This cycle, when continuously reinforced, leads to chronically elevated cortisol levels. And chronically elevated cortisol levels have been tied to an increased risk of serious health problems, including depression, obesity, metabolic syndrome, Type 2 diabetes, fertility issues, high blood pressure, heart attack, dementia and stroke.
(Catherine Price. www.nytimes.com, 24.04.2019. Adaptado.)
Num mundo cada vez mais globalizado, o fato de as ciências naturais falarem uma única língua universal e operarem sob uma única metodologia ajudou paradoxalmente a concentrá-las nos poucos centros com recursos adequados para seu desenvolvimento, isto é, nuns poucos Estados ricos altamente desenvolvidos. Os cérebros do mundo, que na Era das Catástrofes (entre 1914 e 1945) fugiram da Europa por motivos políticos, desde 1945 foram drenados dos países pobres para os ricos por motivos sobretudo econômicos. Nas décadas de 1970 e 1980, os países capitalistas desenvolvidos gastaram quase três quartos de todos os orçamentos do mundo em pesquisa.
(Eric Hobsbawm. Era dos Extremos, 1995. Adaptado.)
De acordo com o excerto, a globalização
O período mais produtivo da Época de Ouro da MPB coincide, basicamente, com o Estado Novo (1937-1945), implantado por Getúlio Vargas. Não é uma simples coincidência. Em 1937, Vargas criou o Ince (Instituto Nacional de Cinema Educativo), o SNT (Serviço Nacional de Teatro) e o INL (Instituto Nacional do Livro). De outro lado, Vargas também operava, com mão de ferro, o famigerado DIP (Departamento de Imprensa e Propaganda).
(José Arbex Jr. e Maria Helena V. Senise. Cinco séculos de Brasil, 1998. Adaptado.)
Durante o Estado Novo,
Observe as obras que representaram, posteriormente aos fatos, os processos de independência da Venezuela e do Brasil.
Nessas representações, pode-se observar
O avanço das culturas sul-americanas nas zonas tropicais africanas conhece três etapas. Num primeiro tempo, a América exporta mandioca através da Guanabara e do litoral vicentino. Numa segunda etapa, a mandioca, o milho, a batata-doce e frutas sul-americanas passam a ser plantados nas terras africanas. Num terceiro tempo, tais culturas espalham- -se pelos sertões africanos. O uso do milho e da mandioca como ração dos povos da região permitiu que os guerreiros negreiros dilatassem suas áreas de captura. Roças de mandioca e milho são abertas nas áreas de parada e descanso dos bandos, facilitando o transporte terrestre de um maior número de cativos do sertão.
(Luiz Felipe de Alencastro. O trato dos viventes, 2000. Adaptado.)
O historiador
Leia o excerto sobre a preparação dos rapazes na Grécia Antiga para exercer seu papel de cidadão e pai de família. Dois tipos de iniciação persistiam nas épocas clássica e helenística em Atenas. A primeira, de origem mais arcaica, era a apresentação do adolescente à fratria1 paterna, inicialmente em um sacrifício oferecido pelo pai aos deuses Zeus e Atena. A segunda, provavelmente estabelecida na época clássica, era o serviço militar, chamado efebia. Ambas tinham igual importância para os gregos do período, e era indispensável que o jovem passasse pelas duas.
(Maria Beatriz Florenzano. Nascer, viver e morrer na Grécia Antiga, 1996. Adaptado.)
1 fratria: grupo de pessoas que acreditavam ter o mesmo ancestral.
De acordo com o excerto, tornar-se cidadão em Atenas dependia
Considerado um dos maiores do mundo, o mapa de Urbano
Monte, elaborado no século XVI, apresenta como particularidade a
De acordo com o geógrafo José Carlos Ugeda, além dos claros riscos de incêndios florestais, as queimadas podem — a longo prazo — destruir a “vida” do solo.
(Fabio Manzano. www.g1.globo.com, 23.08.2019. Adaptado.)
A destruição da “vida” do solo está relacionada, neste caso,
com
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