Academic Earth is a site that hosts thousands of video lectures in over a dozen categories, from researchers, lecturers, and scholars from Universities like Yale, Harvard, Stanford, and MIT.
Academic Earth offers something mentally stimulating to watch about topics you've always been curious about such as astronomy, economics, biology, or political science. The service hosts over 15,000 videos across 17 subjects. Many of them are lectures dedicated to a specific topic that you may want to learn more about, but many of them are generic introductions and talks that you can jump into without any prior knowledge of the topic.
For example, the MIT lecture Physics I: Classical Mechanics, by Walter Lewin, can explain to you why two objects that fall at the same rate from heights even if one is much heavier than the other. Similarly, if you're a fan of ancient history, there's the Introduction to Greek History lecture, taught by Yale professor Donald Kagan.
If you find a topic that interests you, you can browse the available lectures and the grades that other viewers have given the lecturer to see if you might be interested in watching it. Each lecture has its own page and description, and you can watch the lecture in your browser like any other Web video. If it's one in a series of discussions, you can see the entire series of lectures and start from the beginning, or subscribe to the lecture series as a podcast. Many of the lectures include transcripts, citation information, and related documents and figures that you can see through links on the lecture page.

Academic Earth is a great way to spend some time learning something new if you're looking to expand your horizons and a good starting point if you're interested in a subject you never studied or pondering going back to school. There are plenty of pragmatic lectures as well, so if you're looking specifically for talks that will help you invest properly, understand copyright law, or start your own business, Academic Earth has videos for you.
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