Jump to content

Janus

Resident Experts
  • Posts

    2154
  • Joined

  • Last visited

  • Days Won

    37

Janus last won the day on December 28 2023

Janus had the most liked content!

3 Followers

About Janus

  • Birthday August 28

Contact Methods

  • Website URL
    http://

Retained

  • Atom

Profile Information

  • Favorite Area of Science
    physics

Recent Profile Visitors

The recent visitors block is disabled and is not being shown to other users.

Janus's Achievements

Primate

Primate (9/13)

1.2k

Reputation

  1. Ants can do this because of something called the square-cube law. When you increase the size of something by a given factor you increase its surface area and the area of its cross-section by that factor squared, and it volume (thus its mass) by that factor cubed. The strength of limbs are dependent on the area of their cross-section. Which, as the size increases increases at a slower rate than the mass/weight of the animal. Increase an ant to the size of a man, and it wouldn't even be able to support its own weight. Conversely, shrink a man down to the size of an ant, and they'd put a ant to shame in terms of strength. So in terms of higher gravity, this just means that smaller animals would generally fare better.
  2. TIL that I was born on a continental divide. I was born in the Mesabi range in MN, which I learned is part of the Laurentian continental divide.( a dividing line between which way water flows to the ocean.) It is one of 6 in North America: Great, Arctic, St. Lawrence, Laurentian, Eastern, and Great Basin. In addition, where I lived was also where the St. Lawrence divide meets up with the Laurentian divide.
  3. Approval ratings in today's political climate are a bit meaningless. How many disapprove because they think he's "too far to the Left?" and how many because they think he's "too far to the Right" How many give him a poor rating based on just one single issue? etc.
  4. Again, F=ma merely gives a relationship between force, mass, and acceleration. It does not have anything to do with push or pull. It gives the magnitude of the force required, and isn't concerned as to the nature of, or how this force is provided. Here is another equation : F= mv2/r It tells you how much force is needed to constrain a mass to moving in a circle with a radius of r if it has a mass of m and has a speed of v. It makes no difference as to how that force is applied. It can be by a rope anchored at the center of the circle, a rocket engine mounted on the mass applying inward thrust, by the gravity of a central mass, or by the friction between a car's tires and the road.
  5. It is really important to grasp what the variables mean in each equation. In F=ma, we are talking about the amount of force needed to give a mass of m an acceleration of a With F = GMm/d^2 we are talking about the gravitational force acting between masses M and m at a center to center distance of d. To make this clearer, F is often written as Fg Now if we were considering how much acceleration mass m would undergo as the result of gravitational attraction between m and M, Then we we are saying that Fg is assuming the role of F in F=ma or that F=Fg thus we can substitute ma for Fg to get ma = GMm/d^2 cancel m on both sides of the equation and get a = GM/d^2, which tells us that the acceleration of m due to the gravitational attraction is independent of the magnitude of m's mass.
  6. As I already noted, 28,437 kph falls a bit below that for even a near surface orbit. To be lifted off "into space", using the Kármán line (at 100 km altitude) for the boundary of space, you would need to be moving at 28,498.5 kph. In which case, you would rise to a height of 100 km (the apogee of your orbit), and then drop back down to perigee at the surface, rise up to apogee... To leave the Earth's vicinity entirely, you'd need to be moving at 40,253 kph ( escape velocity)
  7. 1. It is meaningless to say "spin at 28,437 km", as rotation needs to be measured as angular velocity. (deg/hr, rad/sec. etc.) I know that it is common to express this in terms of tangential speed( in this case, at the equator) But it is sloppy and can lead to misunderstanding. For example if the Earth had a tangential speed of 28,437 kph at the equator, then at 45 north latitude it would only be 20,105 kph As swansont has pointed out there is a speed where the centripetal force (the force required to keep an object moving in circle) and the gravitational force balance out. This would result in the object going into orbit around the Earth. Gravity is still in play. In fact it is gravity that would prevent someone standing on the equator from just shooting out into space at in a straight line instead of just hovering over the Earth. And by the way, your number is a bit low, the equatorial speed would need to be 28463 kph And because of what I alluded to earlier, only someone on the equator would even go into orbit. People elsewhere will feel lighter, and the ground would seem to tilt a bit under their feet ( And even this is an over simplification which assumes the Earth maintains its present shape. If the Earth was indeed spinning this fast, its very shape would change, making it much more of an oblate spheroid.
  8. I wouldn't place too much faith in the polls; as of late, they have been shown to be highly unreliable. Right up to the '22 midterms they were predicting a "Red wave" with Republicans making large gains in the House (60+ seats). In the Ohio election dealing with the Republicans attempt to change the requirements to alter the state constitution, the polls said it was close and could go either way, while in the election it was overwhelmingly rejected. And most recently, a Democrat won in Florida in a red district when polls showed him losing. A lot of this can be put down to the polling methods not keeping up with the times and thus oversampling certain segments of the population and under-sampling others.
  9. While Trump will be sure to fill his administration with yes-men who's only qualifications are a sworn fealty to Trump. What little reining in and push-back he got last time will be nonexistent.
  10. That would only be applicable if you were shrinking the Earth in order to keep all of its mass contained within a sphere with a radius of r as r decreased. As you move towards the center of the Earth this is not the case, as the amount of material within r decreases as you do so and thus M is not a constant throughout the trip. So while at the surface of the Earth Gravitational potential is -GME/rE, at the center, it is -1.5GME/rE Thus the difference in gravitational potential between the surface of the Earth and its center is smaller than that between the surface and an infinite distance, and so would be the time dilation factor difference.
  11. The argument you so often hear is that gun regulations won't stop gun violence. It's the all or nothing approach; that if a regulation doesn't prevent all gun deaths of innocents, it shouldn't be enacted. Saving 10 lives a year isn't worth it, nor is saving 100 or, 1000...
  12. As pzkpfw alluded to, If it requires a new, now unknown, physics to allow for FTL, then it is pointless to speculate about what would happen, because we have no idea what rules we'd have to adhere to in this new physics.
  13. The Republicans have been playing this game with the border for years. They have no interest in dealing with it, as fixing it would give them one less thing to complain about, and all they have to run on are grievance issues.
  14. Agreed, the.. is a silly one. Good thing for the big bang model that it doesn't claim this.
  15. They didn't. The Babylonians divided the circle in 360 degrees. They then defined a "degree of time" as how long it took the Sun to travel 1 degree in the Sky, which they then divided into 60 minutes of 60 seconds each( we still see this in the practice of measuring angles in degree, minutes, seconds.) Thus the Babylonian minute and second were not the same duration as our modern one. The division of the day into hours was an invention of the Greeks. It wasn't until the middle ages that the two systems were combined, making the hour divisible in the same way that the Babylonian degree of time was. So, there is no mystery, as it is the result of cobbling together two different time keeping systems.
×
×
  • Create New...

Important Information

We have placed cookies on your device to help make this website better. You can adjust your cookie settings, otherwise we'll assume you're okay to continue.