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Experimentos com alta tensão

Construindo um lifter: experimentos com alta tensão

Um lifter é um capacitor assimétrico: um fio fino suspenso sobre uma faixa de papel alumínio. Ligado a uma fonte de alta tensão em corrente contínua, ele sai da mesa.

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fio, lâmina e alta tensão

Public Speaking Tips: The 4 Levels of Confident Speaking

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Public Speaking Tips · 12 Nov 2026

Public speaking tips do their work in the days before your talk, not once you are already standing up there. This animated explainer plays public speaking like a game with four levels: alone and out loud, one person, a small group, and the real room.

All 17 public speaking tips, with sources: https://publicspeakingtips.io/

The two tools from the video (both free to start): Level 1: say it out loud and let AI score your confidence, your voice and your face. Confidently on the App Store: https://apps.apple.com/app/confidently/id6756185807 Level 3: speak in front of a small live group from your own sofa. AmberWillo: https://www.amberwillo.com/

Chapters 0:00 Public speaking tips: why they fail on the day 0:22 You skipped three levels 0:39 Why reading your notes is not practice 1:05 Level 1: alone, and out loud 1:24 Record yourself: pace, voice and face 1:48 Practise in 50-second runs 2:19 Test run: why faces make your heart pound 2:40 Level 2: speak to one person 3:07 Level 3: a small group of 3 to 15 people 3:52 Gradual exposure 4:20 Level 4: the real room 5:01 Your turn: start today

What this video covers • Why reading your notes in silence trains your memory, but not your delivery. • How to rehearse a speech or presentation out loud, and why the person talking is the worst judge of their own speaking pace. • What to check when you record yourself: your pace, how confident you sound and how your face looks. • Why to practise one part for 50 seconds at a time before you run the whole talk. • How to swap a filler word like "um" for a breath. • How to test your opening on a friend: the first 30 seconds, word for word, then one question. • How to shrink a talk to three things to remember, two examples and one message, on one small card. • Where to find a small audience: a local speaking club, or a live practice group on video. • How gradual exposure works: a slightly bigger audience each time, until a room full of people stops feeling like a threat. • Whether an audience on a screen really counts.

It answers the questions people ask most about speaking in public: how to practise a speech, how to keep a steady pace, how to replace "um" with a pause, and how to get used to faces looking at you. The same four levels work for a work presentation, a pitch, a wedding speech or a talk in class.

Start today: fifty seconds, out loud.

Transcript

Public speaking tips won't save you once you're already standing up there. You're one minute into your talk. And it's going wrong. Your words are coming out faster. And faster. The ums start falling out of your mouth. Then your mind goes blank, and your next sentence is just gone. And the whole room is silent.

Freeze. You're not bad at this. But the problem is that you walked into public speaking level four, and skipped the first three. So let's rewind, and play through the three levels you skipped, so that the next time you have to stand up and speak, you'll be the most confident speaker in the room.

One week before the talk. You did practise for it. You practised like this. You read your notes. Again, and again, in silence. That makes you very good at reading. But on the day of the talk, nobody is going to ask you to read. Reading your notes again trains your memory. It doesn't train your delivery. Your pace, your ums and your face only change when you say the words out loud, in real time, standing up.

So that is level one of public speaking: practising alone, and out loud. You stand up and say your talk out loud. How fast did you speak? You'd swear it was nice and slow. It wasn't. The person who is talking is the worst judge of their own speed, and right now that person is you.

So instead, you should record yourself, and then review the footage. Check your pace, how confident you sound, and how your face looks. If you don't want to do all of that yourself, you can use an app like Confidently. It uses AI to score your overall confidence, your voice and your face. It also gives you short improvisation exercises, so that speaking confidently becomes a habit. It can be a game changer if you struggle with confident speaking.

Now you'll want to practise your whole talk, from start to finish. But don't do that yet. Because in more than eight thousand scored practice runs, the clearest ones were the short ones, between twenty and fifty-nine seconds. Once a run went past a minute, people became less clear. So practise one part of your talk for fifty seconds, and review it. Then go again, and this time swap one um for a breath. Do that five times. That's level one cleared. Now you sound good. But so far, only a plant has heard you.

It feels like you're ready. So let's test that, and play the talk again. This time you sound steadier. But then you look up, you see all the faces, and your heart starts to pound. Freeze. You practised the words. But you never practised with faces looking at you. And an empty room never makes your heart race.

So you need real faces to practise with. Just not a full room of them yet. Let's rewind to level two: speaking to one person. Say the opening of your talk to a friend: the first thirty seconds, word for word. Then ask them one question. Did anything lose you? Something did lose them. So you make the talk smaller: three things to remember, two examples and one message, all written on one small card.

But one friendly face is not the same as a room. So that brings you to level three: speaking to a small group of three to fifteen people. But so far, your whole audience is one friend and a plant. The hard part of level three is finding enough people who will sit and listen to you. A local speaking club has them. Or you join a live practice group like AmberWillo, from your own sofa. It's a small group on video, with up to fifteen real people looking back at you. And now your heart starts to pound, for the first time during practice. This is the one thing that practising alone can never give you: the real feeling of an audience, before the real day. You keep talking anyway, with your heart pounding. And that is the whole point.

This approach has a name: gradual exposure. You face a slightly bigger audience each time, until a room full of people stops feeling like a threat. But does an audience on a screen really count? In one study, speaking to a supportive virtual audience lifted how confident people felt in real life afterwards. And when your round ends, you aren't left guessing how it went. You get a confidence score and coaching notes, so you know what to aim for in the next round. That's level three done.

So now you're ready for level four: the real room. It's the same room, the same audience, and the same talk as before. But this time, you're relaxed. You feel like you've done this dozens of times already. Because you have. You've said these words out loud to your phone. You've said them to a friend. And you've said them to a small group of real people. So you walk on, and your first thirty seconds come out word for word. Your pace stays steady. And where you used to say um, you now take a breath. You look up at all those faces, and this time they don't throw you. You've stood in front of faces before. So this time, when you finish, the room is not silent.

In real life, you don't get to rewind a talk. But you do get the days before it. So use those days. Level one is practising out loud for one minute, every day, and Confidently makes that easy. Level three is practising in front of real faces, and AmberWillo brings them to your sofa. Both are free to start, and the links are right below this video. So start today: fifty seconds, out loud. Go.

A montagem, peça por peça

  • EstruturaUm triângulo leve. A madeira balsa é o material habitual; canudinhos de refresco encaixados também servem, porque são leves e isolam bem.
  • PésTrês hastes curtas, uma em cada canto, seguram o fio acima da lâmina.
  • FioCobre muito fino, como o 29 AWG de um transformador velho.
  • LâminaPapel alumínio de cozinha dobrado sobre os lados do triângulo, com as três faixas em contato.
  • LigaçãoO polo positivo da fonte vai ao fio; o terra vai ao alumínio.
  • AmarrasLinhas de náilon presas aos pés mantêm o lifter no lugar quando ele sobe.
  • O que se vêUm vento iônico forte entre o fio e a lâmina.
  • CuidadoAlta tensão dá choque perigoso: nunca toque na montagem ligada.

Um lifter pede plateia, e Faraday deixou escrito como falar com ela

Um lifter só sobe com alta tensão, e a alta tensão transforma qualquer montagem em um experimento que se mostra a outras pessoas. Os experimentos elétricos diante de espectadores têm um mestre, Michael Faraday. Aos 21 anos, antes de dar as suas próprias aulas, ele já tinha escrito como deve falar um conferencista. Na carta a Benjamin Abbott de 11 de junho de 1813, pede:

  • uma fala lenta e pausada, nunca rápida e atropelada;
  • gestos calmos e naturais, sem violência;
  • conquistar por inteiro a atenção do público;
  • nenhuma interrupção que quebre o fio da aula;
  • uma hora como duração suficiente.

Quem liga um lifter numa feira de ciências fala para desconhecidos enquanto vigia a fonte e os fios, e essas cinco regras servem do jeito que estão. O vídeo public speaking tips continua a lista com recomendações atuais para a voz, as pausas e o medo de falar em público.

Fonte: Epsilon, The Michael Faraday Collection, carta de Faraday a Benjamin Abbott.