What Physics Teachers Get Wrong About Tides! | Space Time | PBS Digital Studios
Why Physics Stack Exchange recommends it
Physics Stack Exchange answerers and commenters link it when asking about tides, tidal forces and the Moon's recession, because it gives a clear explanation of the differential-gravity picture that textbooks often get wrong.
Recommended by 4 people across 4 different months, 2018 to 2024.
What it is
A 15-minute PBS Space Time episode hosted by Gabe Perez-Giz that corrects the common 'bulge' picture of tides. It explains tidal force as the difference in gravity across an extended body, why this squeezes and stretches the oceans, and why small bodies of water like lakes show no noticeable tides.
What people said
Recommends DWin · 2018-01 · Physics Stack Exchange · on “Determining Average Tidal Effects”
The variations are not just "due to coastline and shoreline differences" although there is the famous example of the Bay of Fundy. They are also due to the fact that the oceans are constrained by large land masses, so that they are essentially shallow bowls of water being "rocked back and forth" by the Moon and Sun. There are several locations in the middle of the Pacific that have very low tidal excursions because the global scale 2D standing wave has a node in that region. These notions are referenced fairly well in the Wikipedia article on Amphidromic Points [LINK] The mechanism of tides is convincingly explained as a "fake force" generated by integrated "squeezing" across planetary sized
Recommends yathish · 2019-05 · Physics Stack Exchange · on “How is high tide related to tidal bulge?”
You haven't understood my confusion exactly, but thanks anyway. This [this video] video helped clarify my confusion. It's the cumulative squeezing affect that creates the tides and not just the gravity of moon and sun. The reason we don't see tides in lakes is because the cumulative squeezing is not significant compared to the huge oceanic expanse.
Recommends mmesser314 · 2023-07 · Physics Stack Exchange · on “Does the Earth experience air resistance?”
@dan - Tides do slow the Earth's rotation. They are more complex than you would expect, and often explained incorrectly. Here are a few videos. From NASA, what the tides really look like - Global Ocean Tides [LINK] . From PBS SpaceTime What Physics Teachers Get Wrong About Tides! [this video] . From CrashCourse, how they slow the Earth - Tides: Crash Course Astronomy #8 [LINK]
Recommends Léo Vacher · 2024-02 · Physics Stack Exchange · on “What happened to Newton 3rd law if our Moon is moving away at 1.5" yearly?”
Both the moon and the earth are affected by the force of gravitation of one another with the same magnitude according to Newton's third law. What matters here is the tidal forces (the fact that the gravitational force is not acting identically everywhere). For a clear explanation see this video from PBS space-time: [this video] . In the end these tidal force act as a friction that get dissipated as heat and make the system earth/moon loose energy and angular momentum, explaining why the moon is getting further away. Edit: The total angular momentum must be conserved and simply transferred from the earth slowing down to the moon. See comments below.