Ocean tides are primarily caused by the gravitational pull of the Moon and, to a lesser extent, the Sun. The Moon's gravity creates bulges of water on both the side of Earth facing the Moon and the opposite side. As Earth rotates, these bulges move around the planet, causing the cyclical rise and fall of sea levels we experience as tides. The Sun's gravity also influences tides, creating smaller bulges. When the Sun, Earth, and Moon align (during new and full moons), these bulges combine to produce larger spring tides. When the Sun and Moon are at right angles to each other (during first and third quarter moons), their gravitational forces partially cancel, resulting in smaller neap tides. The complex shapes of ocean basins and coastlines also affect the timing and height of tides at specific locations. Friction between the tides and the ocean floor gradually slows Earth's rotation, lengthening the day by a very small amount over time.
This blog post explores creating spirograph-like patterns by simulating gravitational orbits of multiple bodies. Instead of gears, the author uses Newton's law of universal gravitation and numerical integration to calculate the paths of planets orbiting one or more stars. The resulting intricate designs are visualized, and the post delves into the math and code behind the simulation, covering topics such as velocity Verlet integration and adaptive time steps to handle close encounters between bodies. Ultimately, the author demonstrates how varying the initial conditions of the system, like the number of stars, their masses, and the planets' starting velocities, leads to a diverse range of mesmerizing orbital patterns.
HN users generally praised the Orbit Spirograph visualization and the clear explanations provided by Red Blob Games. Several commenters explored the mathematical underpinnings, discussing epitrochoids and hypotrochoids, and how the visualization relates to planetary motion. Some users shared related resources like a JavaScript implementation and a Geogebra applet for exploring similar patterns. The potential educational value of the interactive tool was also highlighted, with one commenter suggesting its use in explaining retrograde motion. A few commenters reminisced about physical spirograph toys, and one pointed out the connection to Lissajous curves.
Summary of Comments ( 3 )
https://news.ycombinator.com/item?id=43697252
HN users discuss the complexities of tidal forces and their effects on Earth's rotation. Several highlight that the simplified explanation in the linked NASA article omits crucial details, such as the role of ocean basin resonances in amplifying tides and the delayed response of water to gravitational forces. One commenter points out the significant impact of the Moon's gravity on Earth's angular momentum, while another mentions the long-term slowing of Earth's rotation and the Moon's increasing orbital distance. The importance of considering tidal forces in satellite orbit calculations is also noted. Several commenters share additional resources for further exploration of the topic, including links to university lectures and scientific papers.
The Hacker News post titled "Ocean Tides and the Earth's Rotation (2001)" linking to a NASA article about tides has a moderate number of comments, exploring various aspects of the topic.
Several commenters discuss the complexity of tidal forces and the factors influencing them. One points out that the simplified explanation presented in the linked NASA article doesn't capture the full picture, as the actual tidal bulge is significantly offset from the direct line between the Earth and the Moon due to the Earth's rotation and the inertia of the oceans. This leads to a discussion about the lag in the tidal bulge and its effect on the Earth's rotation, with one user explaining how this lag creates a torque that gradually slows down the Earth's spin and transfers angular momentum to the Moon, causing it to recede from Earth.
Another commenter dives into the impact of continents on tides, noting that they complicate the picture further by obstructing the free movement of water and creating different tidal patterns in various locations. A subsequent reply elaborates on how the shape of ocean basins and resonances can amplify or diminish tidal effects.
Some comments focus on the long-term consequences of tidal forces. One user discusses the eventual tidal locking scenario, where the Earth's rotation would synchronize with the Moon's orbit, leading to a situation where the same side of the Earth always faces the Moon. Another commenter mentions the impact of solar tides, although acknowledging they are weaker than lunar tides.
A couple of commenters offer additional resources, such as links to websites with tide predictions and a Wikipedia page on tidal acceleration. One user humorously suggests that the slowing of Earth's rotation is a good thing, as it gives us all slightly longer lifespans.
While there isn't a single overwhelmingly compelling comment, the discussion as a whole provides valuable insights into the intricacies of tides and their effects on the Earth-Moon system, going beyond the simplified explanation provided in the linked NASA article. The comments highlight the importance of factors like the Earth's rotation, the inertia of the oceans, the shape of continents and ocean basins, and the gravitational influence of the Sun.