Speed

speed is cool and all but have you ever heard of
✨ acceleration ✨
- Constantly
- Yes. This is when you are really good at making your food last longer.
  
  You're thinking of refrigeration.
  Acceleration is when matter in space starts to coalesce into stellar objects.

1.) 0.28 g 2.) 15.7 g 3.) 0.0034 g
I assumed 1m radius for the first and 5m for the second, particularly the second sounds off. Anyway... The centripetal force from Earth's rotation is quiet negligible compared to its gravitation.
- 5 meters is definitely way too short for the chair swing ride. Look at the people in the seats. It's definitely at least 10 meters.
  Assuming 10 meters and 100 km/h, that gives about 7.9 g. That's in the range of what fighter pilots might experience and well beyond where most people black out, so that's still definitely too high.
  Looking it up online, this is a pretty classic physics problem and the numbers you might see around it are closer to a radius of 12 meters and a speed of 13 to 17 m/s. Taking that as 15 m/s (54 km/h), that works out to about 1.9 g, which I can subjectively say feels much closer to the real value if you ever ride on one of these.
  So, the second one is about 1.9 g
  
  Yeah, those rides complete a rotation in ~10 seconds given what I was able to count in a couple YouTube videos, so 36°/sec. If they have a 10m radius, the linear velocity would be 6.283 m/s or 22.62km/he.
- The 100 km/h seems a bit much to me, too, but I'm having a hard time finding info on the speed of these...
  
  Looked up a video of a gentle one. A revolution takes about 2𝜋 seconds, at which the speed in m/s is the same as the radius in meters, or around 5. Multiply by 3.6 to convert into 18 km/h, which seems realistic for the milder ones. The apparent horizontal centrifugal acceleration will then be 𝑣²/𝑟 = 5 ms⁻² ≈ 0.5𝑔, which corresponds to an angle of approx. 26° from the verical, reasonably close to the video.
  The one depicted in the image probably goes about 2x as fast, pulling perhaps 2𝑔 horizontally for an angle of approx. 63°.
- Considering most people will start to lose consciousness and risk heart issues at like 5g, I’m pretty sure the speed is way off on number 2.
  
  That’s what the juice is for, inyalowda

Thus neatly making the case that radius matters.
- Girth, you say?
  
  One is but a two pi greater version of the other.

I once lived with a sort of science ~~skepticist~~denier (didn't believe in the moonlanding nor did he believe that the earth wasn't flat). He was of the belief that scientists are deceiving the public and one of the examples he gave was that they claim that the earth rotates at 1 670 km/h but if we look outside that's very clearly not the case and if jump we aren't flung at that speed to the side. I spent half an hour in a back and forth trying to explain the concept of relative velocity and inertia. It didn't go anywhere.
Edit: changed to denier based on the comment by logos.
- Ask them to jump inside a train
- Not to be pedantic but I would call them more of a science denier than a skeptic. It's too close to scientific skepticism which is completely different.
- My aunt once mentioned that if the earth wasn't rotating that we'd all be crushed by gravity, and it's only the spinning cancelling out that force. I responded by pointing out that gravity is also present at the poles, where you can casually walk faster than the rotation of the earth, and yet no one has been crushed to death there. She responded that it must be something to do with the magnetic fields, and wouldn't listen to anything I said when I tried to explain the basic concept of angular velocity.
  
  By this logic uh, you'd be crushed to death on Mercury or the Moon as they are both basically tidally locked, and also apparently helicopters don't need blades, fence posts or pool noodles would negate gravity, because they spin really fast.
  Perhaps she saw that one weird Russian experiment from the 80s that concluded that if you spin something really fast it gets lighter, and thus gravity has something to do with spinning? I have seen a whole lot of spin related anti gravity nonsense on the internet.
  Many of the 'electric universe' people seem to think electromagnetism somehow plays a more important role in... what we typically think gravity does... than gravity.
  Ask her if she thinks things get crushed on the North or South poles of Mars. Semi-comparable amount of mass, nearly identical rotation period, but basically no electromagnetics to speak of.
- Have him drop a tennis ball in a moving vehicle. It won't make him understand but you can at least say you tried.

Earth is merely spinning at 15 degrees per hour.
- So one turn takes about... 24h?
  
  Nobel prize coming your way
  
  Oh my god.
  
  Yes, that's how the day and night cycle works
- I feel like this is the most concise answer in this thread.
  Omega squared baby!

acceleration is the answer
- Yes, and a = v^2/r.
  Merry-go-round: small radius, big acceleration!
  Earth: big radius, small acceleration.
- Lol, guys it's not acceleration it's just the exact definition of acceleration. Which is definitely not acceleration.
  
  None of those reference frames are accelerating.
  The difference is whether there is a changing velocity or not.
  I'm going to assume that you're defining acceleration in that second statement, because I'm not sure if you are and "changing velocity" is literally what acceleration means. In any case, both acceleration and velocity are vectors, both have a direction, and so a person's velocity sure as hell can't be constant when they're going in circles. Ergo, acceleration. I mean that's what force is, mass times acceleration, so if you move and you can feel it you're accelerating. Earth has gravity that can more than cancel it out, but we can't say the same for rides.
  Somebody smarter and with more energy than me can probably come up with a rough estimate of the g's being pulled in each picture (ignoring gravity).
  Edit: looks like someone did!
  
  We do understand the difference between speed and velocity. It's just that acceleration is the change in velocity over time, not speed.
  
  What? No, the radius just makes the speed "faster", but what really matters is the frequency of rotation.
  The merry-go-round is what, 20-25 RPM max? The carnival ride is only like 6-8 RPM. Both are a hell of a lot faster than 1RPD.
  
  This is like the lava and red goo thing
  
  Rotation is acceleration towards the center with a velocity perpendicular to the centre. Using a frame of reference that rotates along with the object doesn't change what is physically happening to that object, it just affects the way you observe what's happening. A rotating frame of reference is itself accelerating and each of those frames of reference are accelerating.
  We don't feel the Earth's rotation because gravity is accelerating our entire body and surroundings at the same rate, plus it's not just the spinning keeping us in equilibrium; the left over force holds us on the ground.
  The other two feel different because it's the structures that provide the acceleration towards the centre, which then pushes on our bodies where it makes contact, and then the structure of our bodies pulls the rest and you can feel the forces of things wanting to move in the direction of inertia but being pulled around the circle instead.
  If rotating frames of reference weren't accelerating, turning a car would feel no different from going straight.