What is Earth: Definition and 1000 Discussions

Earth is the third planet from the Sun and the only astronomical object known to harbor and support life. About 29.2% of Earth's surface is land consisting of continents and islands. The remaining 70.8% is covered with water, mostly by oceans, seas, gulfs, and other salt-water bodies, but also by lakes, rivers, and other freshwater, which together constitute the hydrosphere. Much of Earth's polar regions are covered in ice. Earth's outer layer is divided into several rigid tectonic plates that migrate across the surface over many millions of years, while its interior remains active with a solid iron inner core, a liquid outer core that generates Earth's magnetic field, and a convective mantle that drives plate tectonics.
Earth's atmosphere consists mostly of nitrogen and oxygen. More solar energy is received by tropical regions than polar regions and is redistributed by atmospheric and ocean circulation. Greenhouse gases also play an important role in regulating the surface temperature. A region's climate is not only determined by latitude, but also by elevation and proximity to moderating oceans, among other factors. Severe weather, such as tropical cyclones, thunderstorms, and heatwaves, occurs in most areas and greatly impacts life.
Earth's gravity interacts with other objects in space, especially the Moon, which is Earth's only natural satellite. Earth orbits around the Sun in about 365.25 days. Earth's axis of rotation is tilted with respect to its orbital plane, producing seasons on Earth. The gravitational interaction between Earth and the Moon causes tides, stabilizes Earth's orientation on its axis, and gradually slows its rotation. Earth is the densest planet in the Solar System and the largest and most massive of the four rocky planets.
According to radiometric dating estimation and other evidence, Earth formed over 4.5 billion years ago. Within the first billion years of Earth's history, life appeared in the oceans and began to affect Earth's atmosphere and surface, leading to the proliferation of anaerobic and, later, aerobic organisms. Some geological evidence indicates that life may have arisen as early as 4.1 billion years ago. Since then, the combination of Earth's distance from the Sun, physical properties, and geological history have allowed life to evolve and thrive. In the history of life on Earth, biodiversity has gone through long periods of expansion, occasionally punctuated by mass extinctions. Over 99% of all species that ever lived on Earth are extinct. Almost 8 billion humans live on Earth and depend on its biosphere and natural resources for their survival. Humans increasingly impact Earth's surface, hydrology, atmospheric processes, and other life.

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  1. rudransh verma

    B To displace the Earth from its orbit

    We know that the centripetal force and the tangential velocity is responsible for the motion of Earth around sun. Newton’s second law says F=ma. If we all get together(whole population) in one place like parallel to the tangent to orbit and jump can we displace Earth from its orbit?
  2. A

    Calculate the total force on the Earth

    I am confused how I am supposed to figure out the answer if I do not know the mass of the earth? Do I just set it to 1 and use m1 and m2 as ratios?
  3. Remixex

    Estimating the velocity of seismic waves through an idealized Earth

    Hello, this is a repost from a much less-clear question I posted before (link to question: https://www.physicsforums.com/threads/triangles-inside-a-circle-to-represent-raypaths-inside-an-ideal-earth.1011998/#post-6596165). It's kind of a loaded question, however it can be expressed as triangles...
  4. Remixex

    Triangles inside a circle to represent raypaths inside an ideal Earth

    I have managed to get some of the required distances and angles. I have the distance ##a##, the velocity inside the mantle, the total radius of the Earth ##R_t## as well as mantle and core radii. I have also figured out the angle of incidence, however I cannot get the refracted angle with the...
  5. I

    B Gravitational Orbits: How the Earth Knows Where to Go

    How does the Earth's reference frame "know" to experience the gravitational pull of where the sun/Earth barycenter will be in 8 minutes, rather than orbit around the spot where the barycenter was 8 minutes ago? The latter case seems required by the finite speed of gravitation, but coplanar...
  6. A

    Gravitational potential energy traveling from earth to mars

    My attempt: Let ##M_e## be the mass of the Earth and ##M_m## be the mass of the person. Let ##D_{EM}## be the distance from Earth to Mars and let ##R_e## be the radius of the earth. Defining these constants (leaving off units for brevity): Masses in Kilograms (G is not a mass but I'll leave...
  7. A

    Torque imposed by the Moon and Sun on the Earth given its precession

    From the givens: Approximate Earth as a sphere: ##I_e = \frac{2}{5}MR^2 = \frac{2}{5}(5.97x10^{24})(6.371x10^6)^2 = 9.69x10^{37} kg*m^2## ##\omega_e = 7.29x10^{-5} \frac{rad}{s}## To calculate the rate of precession of the disk the Earth precesses around (1 revolution every 26,000 years)...
  8. Lren Zvsm

    Sapient Life Indigenous to a Planet Orbiting a Red Dwarf

    I am considering writing a story that features aliens indigenous to a planet orbiting a red dwarf star. Even so, because of its proximity to the red dwarf, the planet's surface receives much more radiation than Earth's surface does. What is more, the planet has no moon to stabilize its...
  9. A

    I In Freefall orbiting Jupiter versus Earth

    I know that in Earth, an astronaut feels weightless in orbit but actually is not. The astronaut would not feel his own weight until he actually stands on a floor where his feet point towards the Earth as the Normal Force is the perception of weight. So, in Jupiter, where g ~ 25, an astronaut...
  10. ohwilleke

    I How Big of an Object Orbiting Closer to the Sun Than Earth Could Be Overlooked?

    Science involves not just knowing what you know, but accurately estimating how sure you are of what you know and having a decent understanding of what you don't know. There are two known true planets closer to the Sun than Earth (Mercury and Venus, neither of which has a significant moon), both...
  11. godiswatching_

    Engineering Resistance of a wire around the Earth

    Hey! I had a question about this problem. I did (1) Using $$R_{0}=\rho\frac{l}{A}$$ For (2) I assume the question means that the radius increases by a meter. So I used $$\bigtriangleup L = 2\pi (r_{E}+1) - l$$ and then I used that L to find the new R. Then I said $$\bigtriangleup R = R-R_{0}$$...
  12. G

    Satellite orbiting the Earth (heat radiation)

    Mass of a satellite is 750g(##m = \rho V = 8,96 \frac{g}{cm^3}\cdot (\frac{4\pi(100cm)^3}{3} -\frac{4\pi(99,9cm)^3}{3}) = \approx 750g =0,75kg##) I am not sure what to integrate. I solved T there but it seems far stretched $$T =\sqrt[4]{\frac{dQ}{dt}\frac{1}{e\sigma A}} $$ How to get the...
  13. Y

    Considering Earth ground vs floating ground in off grid solar

    Context: I'm building an off-grid, 100% solar powered home. I have a 12 kw solar array wired up to a Sol-Ark inverter and a Fortress 18.5 kwh lithium battery. Question: What is the ideal grounding/earthing scheme? Additional context: where I'm building, there is currently no requirement that...
  14. Joe Bond

    I Can Placing Earth Between 3 Black Holes Slow Down Time?

    I am just wondering if placing the Earth equidistant from 3 black holes that are spinnng would slow down time on the Earth, due to the time dilation effect. Would that give us more time to live?
  15. J

    I Does Escape Velocity depend on a rocket's direction away from Earth?

    He explain escape velocity in example where rocket goes straight up,isnt escacpe velocity ,velocity where centrifugal forces and gravity are equal,so refers only when rocket going in circle/orbit? Can rocket really leave Earth in straight line like he show in video once reach this velocity and...
  16. A

    I Normal force and details of the Earth holding up an object

    It's a simple application of Newton's third law to show that the Earth indeed does accelerate towards an object as it falls towards earth. M_o is the mass of the object M_e is the mass of the earth From the third law (and ignoring air drag): M_e * a_e - M_o*g = 0 (with a up-positive...
  17. H

    I Image for increase in gravitational potential energy in radial field

    A question to physicists: What sort of real world scenario / image would *best* depict the increase in gravitational potential energy in a radial field? Would a rocket traveling through the Earth's atmosphere suffice or are there better alternatives? This image would have to be relevant to the...
  18. T

    How to Grow Crops on a Hotter Earth

    These folks looked to the plants growing on the driest land on Earth -- the Atacama Desert. They collected some plants, soil, and the bacteria in them; then genetically sequenced them to see what's needed; over a 10 year period...
  19. yucheng

    I Reading Paper on Earth Occultation Technique

    The Burst and Transient Source Experiment Earth Occultation Technique https://www.semanticscholar.org/paper/The-Burst-and-Transient-Source-Experiment-Earth-Harmon-Fishman/b4e57f91de6fec73fa680bcd7d6efbdf0de10bee In **Appendix B**, the authors derive the equations for the occultation times...
  20. mncyapntsi

    Centripetal acceleration along a latitude of Earth

    Hello, I am attempting to correctly solve this problem, however I end up with an equation that is slightly different as the one provided in the textbook solution. For question (a) I get the same thing, just instead of cos, I have cos^2 and I can't figure out where I went wrong. My process was...
  21. L

    Earth grounded, where does the current flow?

    My questione are these: -If i have a voltare source (like a battery) that supplies a 5V voltage difference between its terminals, and there is a parth from positive to a resistor and then to ground, with negative terminal not connected: the current flow to the ground?( I believe because there is...
  22. Dennis Plews

    Saving Our Future Earth: Keeping Our Planet in the Goldilocks Zone

    Summary:: A proposal for keeping the Earth intact during the Sun’s Red Giant phase. The following is a hypothetical method for keeping our Earth in the Goldilocks zone during the Sun’s Red Giant phase offered for analysis and critique by those amongst us who are more knowledgeable than I. Your...
  23. B

    B How long it takes the Earth to fall halfway to the Sun--ellipse method

    There's a classic physics problem that is: If Earth is orbiting the Sun at 1 au from and is suddenly stopped. How long does it take to fall into the Sun (neglecting the size of the Sun/Earth)? I know that a clever way to solve this problem is by using degenerate ellipses and an object...
  24. P

    Would the Earth speed up rotating if the molten core solidified?

    The question is simple. The molten stuff inside the Earth will get a smaller volume when it solidifies. Will the Earth increase its rotation speed in reaction to this? What about the magnetic field?
  25. N

    B Star visible for longest time from Earth

    I was just looking up at the stars wondering how long they have been visible for. I started wondering if any of them might have been around this galactic neighbourhood long enough and long lived/old enough that the dinosaurs could have seen it. Do you think they’d be any? If not what might be a...
  26. jaumzaum

    I What's the electric potential of the Earth?

    I was wondering, we constantly assume the reference of zero potential is the surface of the Earth. But if we consider the reference to be the infinity, what would be the electric potential of the Earth? As Faraday says, the Earth is charged with a -580 kC of negative charge. If we consider...
  27. B

    Solid angle in an optics problem (artificial irradiance of the Earth)

    The actual problem can be found as #2 on this link: https://ocw.mit.edu/courses/mechanical-engineering/2-71-optics-spring-2009/assignments/MIT2_71S09_ups1.pdf I rewrote the problem above with the solar irradiance data that they give. My interpretation is of a square 1 m x 1 m plane sitting...
  28. putta

    What is the voltage allowed Earth to Nuteral

    Hi Normally our electrical equipment systems neutral to Earth voltage showing 1.4 to 2 volts AC. Our requirement neutral to Earth is 0 volts. How to achieve this value ,please help me. What is the normal acceptable voltage of neutral to earth.
  29. H

    B Light Leaving Earth-Observer's View of Events in Time

    Would an observer many light years from Earth (and approaching say) see events leading onwards through time (to what level of detail i am not proposing but say weather and maybe Humans on the ground?) in the light received?
  30. S

    I What is the average annual accumulation of cosmic dust on Earth?

    By "accumulation", I mean depth at the Earth's surface (i.e., whatever volume it is would be divided up the surface area). This dust would be from anything (e.g., meteors, stardust, etc.), but would only count stuff that ends up as dust (i.e., no gas or liquid). I guess a follow-on question...
  31. barryj

    Centripetal force on a person on the Earth

    I am confused. See my diagram below. With the Earth rotating, I think the scale would read the force of gravity or 448.4 N. If the Earth were not rotating, would the scale read less or more due to the effect of centripetal force? I tend to think more by an amount of 1.78 N. Is this correct? If...
  32. sophiecentaur

    Earth grounding problems and RCDs (Strictly a UK scenario, I think)

    The story is that I did some wiring additions ` couple of years ago. I extended a Ring Main (cover your eyes dear US readers) and bought one of those socket checkers for a few quid. I have got this far in my life without one but I though why not splash out. The connections, of course, checked...
  33. agnimusayoti

    Calculating the Solid Angle of a Nebula from Earth

    If I assume the nebula is a circle, than the length of arc viewed from Earth is a half of the circumference. So, here $$l = \frac{1}{2} \pi D$$ From the problem, ##D = 125 000 ly##. Because the distance of nebula is much larger than the diameter; I try to approximate R with the distance of...
  34. Vash25

    Gravitational potential energy question -- Ojbect sitting on the Earth

    Good day, If I consider my system to be an object and the earth, and the object is on the surface of the earth, then the system will have gravitational potential energy. Why couldn't I say that only the object (considering it as my system) has gravitational potential energy? Thanks
  35. S

    MATLAB How to plot an orbit around the Earth in MATLAB

    Hi. can you help me to plot orbit around Earth with sphere in MATLAB? I wrote the code that plot 3D orbit but without earth. the code: clear all close all clc R=6371e+3; r0=3e+5; p0=[R+r0;0;0;0;10000;0]; [t,p]=ode45(@sattelite,[0,12000],p0); xout=p(:,1); yout=p(:,2); zout=p(:,3); vx=p(:,4)...
  36. jim mcnamara

    Mars had a Great Oxygenation Event, just like Earth did.

    Mars underwent a biologically induced change (assumption -- via photosynthesis) to the atmosphere billions of years ago. Rock strata were identified that are evidence of an earlier atmosphere, that is different from what came later. The more recent atmosphere oxidized iron in most of the...
  37. Twigg

    Seismic ray-tracing, when does a spherical Earth matter in practice?

    I'm taking a geophysics class and the math makes sense but the context is lost on me. My understanding is that the primary use of seismic ray-tracing is to locate disturbances that cause waves to propagate radially. I also understand that 35km is the depth at which the Earth's spherical shape...
  38. M

    B Biggest asteroid to pass Earth in 2021

    An asteroid that will be the largest during the year 2021 is expected to pass by about two million kilometers from Earth without the risk of colliding with it, but this astronomical event will allow scientists to study this celestial body more closely. This asteroid is called “2001 FO32”, and...
  39. E

    I What if the Earth (and the Universe) were 2d?

    Well, okay, I should say: what does Newtonian gravitation look like in a ##2+1## dimensional Newtonian universe? Consider a flat Earth, i.e. a region ##\mathcal{E} = \{ (x,y): x^2 + y^2 \leq R \}## with mass density ##\rho##, then for ##r > R## a natural guess for the gravitational field seem...
  40. M

    B What Would Happen if the Earth Stopped Rotating?

    If the Earth did not rotate, would one side always face the sun and the opposite side always be in darkness? Or would a day be six months, and a night be six months? Or something else?
  41. bo reddude

    B Why doesn't the Earth at the equator experience a sonic boom?

    The Earth's circumference at the equator is 24,901 miles, or 40.075 million meters. It rotates completely once a day or in 86400 seconds. The speed of sound is 343 m/s and the Earth moves at the equator at 40.075 million m/86400 s = 463.831019 m / s which is clearly faster than the speed of...
  42. W

    Work done to bring the Earth to rest

    I know how to solve this using work energy theorem but how can one solve it starting from the fact that net force is centripetal? My attempt was "this means we only need an "anticentripetal" force of same magnitude, but centripetal force does 0 work hence new force also 0 work to counter it"...
  43. F

    Rocket moving away from the Earth

    I first began to identify the various events in the problem. I call the rocket ##S'## and the Earth ##S##. Sending signal Tail signal reflection Head signal reflection Tail signal return Head signal return For the Earth I know that: ##t_4 = T## ##t_5 = T + \Delta T## Since the two events...
  44. TimeSkip

    Stargazing Will the supernova explosion of Betelgeuse influence the Earth?

    Will the supernova explosion of Betelgeuse influence the Earth's climate and temperature or even the sun in any significant way?
  45. S

    How was Earth flat in Grenvillean?

    It is recently claimed that between 1800 and 800 million years ago, Earth was flat. This is supposedly indicated by lack of minerals that should have formed in mountains´ roots. However, from that period, there are rocks formed in orogeny - mountain forming processes. For example Grenvillean...
  46. cybernetichero

    What WOULD be adequate proof of alien visitation to Earth?

    Perseverance's successful landing has scared up some UFO conspiracists online. I used to be like them and I was into Charles Forte as well, encouraged by people who should have known better (yes I AM looking at you Arthur C. Clarke) until I realized I just really wanted to believe rather than...
  47. S

    Equations for a mass falling to Earth from a distance

    I have a question : If we consider the change in g due to distance from the Earth core; then y=distance from earth’s core t=time G=gravitation constant M=Earth’s mass k=GM $$y^2(t)=\frac{k}{y(t)^2}$$ If we consider air resistive force as proportional to speed squared, then: m=falling object...
  48. L

    Find g, measured to be 9.78 at the equator, when Earth is still

    If we think about the forces acting on an object at the surface of the Earth, these forces would be the weight force (mg) pulling downwards and the normal force (N) acting upwards . If the Earth were to stop rotating, then according to Newton's first law the forces must balance, meaning the net...
  49. A

    Exploring Angular Momentum: Examining Earth & Bike Wheels

    Take for example earth. Earth has angular momentum about its own axis. However, if we ignore the orbital portion, the angular momentum of the Earth relative to the sun's axis is the same. Another example is the spinning bike wheel/person holding it in a chair. It has angular momentum about its...
  50. potatoleg

    Calculate time passed on a ship clock seen by Earth observers

    In this case, γ = 1/√(1-v^2/c^2) = √(1-0.6^2) = 0.8 However, I'm not sure if time observed by Earth is proper time or moving time. The definition of proper time in my textbook states that it is 'the time measured in a frame of reference where the events occur at the same points in space. I'm...
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