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    • What direct evidence do we have that the Earth is spinning? After all, much as in the example from the lecture in which George and Gracie are floating in space, we don’t seem to feel the Earth’s motion. (Hint: Is the rising/setting of the sun convincing evidence? Have you ever encountered a Foucault Pendulum?)

    • I’m a Post Graduate Physicist. Just trying to learn the way to explain ideas to my students. I know every bit of special relatively.

    • Good stuff so far

    • Good stuff. Pretty simple but complicated as well

    • If the earth were orbiting the sun without spinning then shouldn’t the day and night cycle be different from what we observe?

      • Yes, each would take half of a year (6 months of darkness, 6 months of light).

        However, having the perception that the universe is revolving around Earth doesn’t mean Earth can’t be spinning. In fact, that’s exactly how it works with the sun! The sun rotates around its axis about once every 27 days. So even if you were standing on the sun (and able to survive it), you would still see the planets and stars moving across the sky just like we do here–they’d just be moving about 27x slower 🙂

    • We can say Earth is spinning on its axis while revolving round the sun because we experience day and night seperately.If it was not spinning the day and night phenomana i think, would not occur daily , in some place there would be complete darkness and in someplace it would be daytime.

      • It could very well be the case that Earth is just sitting stationary while the entire universe spins around Earth. You would have to argue that objects further from Earth are traveling at speeds much greater than objects closer to Earth, but it would still explain the movement of celestial bodies as we see them.

    • The effects of coriolis acceleration (hurricanes, etc.)

    • We are spinning relative to many other things we can observe in space.

    • Corriolis effect is a good candidate for this matter.

    • I like how simple but yet so complicated the world can be!

    • very helpful.

    • We experience Day and night

    • We experience day and night cycles, and we are not moving in a constant direction.

    • There are various way to feel that the earth is rotating in its orbit→
      1.the day and night effect,
      2.the seasonal changes,
      3 the coriolis force for which the cyclones,hurricanes etc. takes place,
      4.period of Foucault pendulum
      And so on…….

    • We experienced the day and night and also we feels the seasonal changes that’s how we can feel that earth is spinning..

    • From the fact that we experience alternate days and nights at the same location.

    • Professor said that Earth is not Inertial frame for one even if one is at rest on earth.
      What about the case where Greece and Adam are both on earth, at the same time,Greece is at rest and Adam is moving with constant speed towards the East. Both of them will be in Inertial frame with respect to each other.
      In that case isn’t Earth an Inertial frame?

    • Coriolis force and by external satellite perspective

    • I love it that this is free. i’m from teh Philippines I ‘d want my son to learn all this, he’s ten. And we can learn together.

    • If the Earth wasn’t spinning, one side of the Earth would be “day” for months while the other side would be “night”.

      I hope that it’s comprehensible… I have trouble putting my thoughts into words.

    • The Sun rises in the East and sets in the West with a circadian cycle. Also, every night stars/planets rise in the East and set in the West. This is due to Earth spinning not the distant stars actually moving with respect to the Earth, it’s the Earth that is spinning on its axis anti-clockwise.

    • the day and night

    • Great way to begin with!

    • “” “”

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    • Day and night may be an incomplete answer, also seasons as a reflection of the non-perpendicular angle between rotation axis and the Earth’s orbit complements litle more the first statement.
      A test with Foucault Pendulum is good evidence showing that because the Earth spins then the pendulum does not swing perfectly back and forth instead the oscilation plane also rotates a bit with the planet rotation

    • I’m enjoying the progression through the course. Each is building on the previous. Is there a model for describing multiple inertial frames?

    • That’s a pretty easy thing to imagine. Imagine that the earth is still in the center of the solar system. Sun ans other planets revolve around the earth the there should be day in half region of earth for a significant period of time i.e like half a year (if this hypothetical orbit is round). If its is so then the rising and setting must not be around us. And it is impossible for the earth to revolve if it is not influenced by the gravitational force!

    • Assuming that I launch the space craft from the earth such that I can see craft from earth which is moving with same angular velocity as earth in orbit of earth ,if earth is not rotating about its axis then I can see satellite only once in a day (24 hr)but if earth is rotating then I can space craft all the time and that’s cool.

    • We experience day and night cycles on earth. It is the direct evidence for the rotation of the earth. But, in terms of relative motion, we can’t say it in that way. But,stars , other than sun , which are distant to us, and their reference frame wil say that that the earth is rotating anti-clockwise. Eventhough, it is not always right that the earth is an inertial frame. But, to avoid the complications, regarding to the conceptual explanations , we can say that, it is approximately inertial.After all,every thing is in accordance to the perspective.

    • Yes a Foucault-type pendulum will illustrate the turning of the earth. Good natural examples include cathedral chandeliers as in Oxford Cathedral.

    • the day night effect

    • The day and night effect as we wouldn’t be experiencing it if the Earth wasn’t spinning on its axis in a 24 hour cycle.

    • Since Earth is accelerating around the Sun and is therefore not in an inertial frame, doesn’t that mean that it is not a valid perspective to say that the Sun is going around the Earth?

    • The Foucault pendulum proves beyond doubt that the earth is rotating.

    • Before we can even postulate it’s spinning, we need to know (or postulate) it’s a globe! It could have been a disc spinning.

    • Yeah, we have a days and nights due to its rotation and seasons due to its revolution, we can say that earth is spinning just by sitting on our home cause we can feel it

    • The physics of movement of the Foucault Pendulum are easiest explained if the earth is spinning.
      Like wise for the sea level being further from the center of the earth at the equator than else where.

    • I propose to have another look at the universe revolving around Earth. From a certain perspective, everything is revolving around us. Imagine a black hole at the core of the planet, where time and space blend together in an elixir of potentiality. Imagine that same potentiality existing within every individual, within consciousness. Every passing day science fiction becomes theoretical, then likely and baryonic fact. Imagine what the future will hold, because that is what is needed to construct our reality.

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    • What speed do we need to attain if we really want to feel the motion of earth?

    • Good to feel the relativity from his lectures.

    • And?

    • When you on bike and someone is riding at constant speed that moment when you close your eyes, you can’t sense or justify that you are in are simply feels you are at rest.In reality you are in motion but can’t feel or sence.

    • the day and night is the best example to state that earth is moving and changing directions

    • The Earth is constantly changing direction in it’s orbit, as well as spinning on it’s axis – so as Brian stated, any observer on the surface is not in constant velocity but is in fact always accelerating – therefore the observer is technically never in an inertial frame of reference.

    • The coriolis effect and the centripetal force of the earth may be a reason.

    • In my perspective, the evidence that Earth rotates could be the presence of the magnetic field around it. Its only because the Earth rotates, we have magnetic field due to the electric currents in the core of the Earth

    • The pendulum is a prime example.

      But most examples can be explained away using ludicrous assumptions about physics (eg: the entire universe is spinning around Earth with celestial bodies farther from Earth moving faster than those closer). So to be precise, it isn’t enough to say that the rising and setting of celestial bodies is evidence, but that the laws of physics one would derive from observing celestial bodies dictates that Earth must be rotating. All across the universe, objects move around objects larger than themselves–planets around stars and stars around their galaxies.

      That said, from my perspective, Earth is the biggest celestial body I’ve ever seen, so ¯\_(ツ)_/¯

    • And your point is?

    • The Coriolis effect, which can be observed directly, not only indicates that the earth is spinning but that the earth is approximately spherical. Newfoundland tug boat operators towing icebergs south, away from shipping lanes, have to constantly readjust course headings to compensate for the Coriolis effect.

    • We can see from more careful observation that the earth is rotating the first evidence supporting that idea was recorded in 1851 using the foucaults pendulum this Tool amongst other observations confirm to us that rotation is a fact the way in wich the sun moves across the sky day after day when perceived from the same point on earth also confirms this phenomenon.

    • Use a Foucault Pendulum.

    • By using the evidence given by solar eclipse.

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    • We can confirm that the earth is rotating if we observe the motion of Foucalt Pendulum. As the time passes the path of the foucalt pendulum changes wrt ground.It appears to move forward.

    • On the thought experiment of a spaceship accelerating towards the speed of light.
      Since the mass of all objects will increase, so will the the increased mass including higher objects (bodies) inertia
      gravitational space folding around the mass etc.
      This means that if in theory we could accelerate the spaceship continuously at some point before reaching very close
      to the light speed the ship will stop functioning, human bodies will get crushed under their own weight etc.
      And in theory if the acceleration would continue the ship will be crushed in very small singularity before reaching the light speed.
      Am I on the right track here or badly mistaken?

    • Because the earth is in spherical?

    • This is a quote, from my post in the scale thread. It is more appropriate here.

      “If something was, ‘actually’, traveling away from us, at twice the speed of light. We would observe, it travel say, 1 light year, from A, to B. In..
      (1/2 year for object to travel from A to B) + (1 year to see the light of the objects arrival at b) = 1.5 years. And, conlude it traveled at 1ly/1.5y = 2/3rds the speed of light.
      If the object traveled instantaneously, we would see it travel at light speed. We would see its arrival in one year, when the light of it reached us.
      It is intuitive, that nothing can travel faster than instantaneously. Could the ‘speed’ of light limit’, be more to what we can observe, than to actual velocities?”.

      There is a set of equations, to what Bob would see as Alice moves to point B, at velocities that may exeed the speed of light..
      For instance, without time dilation..
      the trip time Bob measures ‘Tb’, equals the trip time alice would measure ‘Ta’ plus’+’ The time it takes the light to reach Bob at A, from B.
      If Alice is traveling away from Bob, he cannot ‘see’ her travel faster than light, no matter how fast she goes. Unless, she can travel pastward in time.

      This qualitatively suggests to me, that this speed of light limit, might just be to our ability to observe, at the speed of light.
      But, Bob calculates, with the equations of special relativity, that Slice will experience, ‘time’ dilation’.
      For Alice’s clock time to agree with Bob’s calculation, Alice would have to actually experience a time dilation, (Ta(1+2Va/c, if I recall correctly) during her trip time at her actually faster velocity. :shrug:

    • It occurs to me. That as the mass you must accelerate increases. So also, would the mass of whatever energy source you are carrying with the ship to create the force for acceleration. :shrug:

    • Actually I don’t know, what this “mass” is, that increases. ‘Inertia’? That’s why I’m here.

    • “Sun rises in the east and sets in the west” it may be a evidence, i think

    • We can say Earth is spinning on its axis while revolving round the sun because we experience day and night seperately.If it was not spinning the day and night phenomana i think, would not occur daily , in some place there would be complete darkness and in someplace it would be daytime.

    • Day and Night

    • 1. Day/night shift. One may say that the effect would be the same if the Earth was stationary and the universe was rotating around it but a) we can justify position by several objects like sun and distant stars b) actually it doesn’t matter what rotates around what because if the observer (center of coordinate system) is outside The Earth, the planet woudl spin even if it stationary but the Unverse rotates around it)
      2. Coriolis force – ocean streams, constant air streams like passats etc
      3. Different steepnes of river shores for the rivers flowing from South to North (for example in Siberia and Africa)
      4. At last Foucault pendulum

    • The issue is explained in an interesting way.

    • Day and night plus seasonal characteristics are evidence of movement

    • changings of days and nights and seasons are the clear evidence of earth is spinning.

    • Earth is spinning on its axis while revolving round the sun because we experience day and night separately. If it was not spinning the day and night, would not occur daily. Seasons change is another evidence.

    • Hello Ladies and Gemtlemen,

      When as a kid we went to a museum, there was a huge Foucault Pendulum there – 40×40 or so. I think the museum was in Ottawa, the capital of Canada. Of course the gyrations of the earth cause the pendulum.

      Galileo would use the moons of Jupiter to aide his bag of measuring tools that could also monitor time, perhaps his mind allowed for the earth spinning around. This was the reason he was on trial with the church- his revolutionary revolution.

      Proof that the earth is spinning may include biological life on earth, but that may be conditional upon the earth breaking the speed of the sound barrier. We do not see the ESI – earth similarity inventory list this factor.

      The place the moon rises and sets allows people to think that in the moons 18.5 year cycle of wobbles that the earth spins.

      Corealis winds show mirror images in north and south topographies, indicating spin.

      Shadows indicate spin.

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    • Science, day night cycles, seasons, weather patterns, etc. etc. etc.

    • What direct evidence do we have that the Earth is spinning?
      Well one direct evidence that we can see is how the day and the night comes into our sight if not we wouldn’t see the difference between day and night.
      Other evidence would be the weather and the seasons of the earth and this is a direct cause of the spinning of the earth.

      Have you ever encountered a Foucault Pendulum?
      Once I saw a Foucault Pendulum in a museum.

    • Well one direct evidence that we can see is how the day and the night comes into our sight if not we wouldn’t see the difference between day and night.
      Other evidence would be the weather and the seasons of the earth and this is a direct cause of the spinning of the earth.

      Once I saw a Foucault Pendulum in a museum.

    • re: evidence that Earth is spinning
      I think the evidence would be that the movement of the other planets etc. relative to Earth would be very complex, and there is no force acting on them to cause all that extra movement. The gravitational forces that we can measure only line up with all the movements when we put the sun at the center.

    • Excellent material so far… The theory of relativity will always be fascinating to me.

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