FlyJunior172
FlyJunior172 t1_iugwhkp wrote
Reply to (eli5) how fast would a cylinder that is 3cm wide, 15cm long, and weighing 1kg accelerate through atmosphere, if given a constant thrust of 2500kg. (for the sake of air resistance assume the cylinder is vertical in relation to the thrust.) by dudewasup111
There’s not actually enough information here to solve this problem.
Here’s why: force is the product of mass and acceleration. It can also be defined as the derivative (or rate of change) of momentum. We’ll use the first definition here. In the metric system, force is measured in newtons, abbreviated N with base units of kg·m/s². In imperial, that unit is pounds, abbreviated lb with base units slug·ft/s². So now what we have is a stick that we know weighs 9.8N, and an applied load that we can’t use because it’s given in units of mass.
Now, if for example, the applied load were equivalent to an object that would show as 2.5Mg on a bathroom scale, then the base acceleration becomes easy to find. We sim the forces and divide by the mass of the stick: ((2500×9.81)-9.81)÷1=24515.191406 m/s²
But there’s another problem: without knowing more about the stick, we can’t really calculate drag. We’d need a wind tunnel for that. See, drag is a finicky thing that depends a lot on the surface of the object moving through the fluid. Without knowing more about the object, form drag is the best we can calculate, and even that can get fiendishly complicated.
FlyJunior172 t1_iugqqcj wrote
Reply to ELI5: if Earth rotates so fast, why does it always look still from outer space? by ShesOver9k
The numbers you’re hearing are linear speed, not angular speed.
vᵣ=rω where v is the linear speed, r is the radius of rotation and ω is the angular speed.
For earth, r = 3950 mi, and ω = 15°/h. This gives vᵣ= 3950×15×π÷180=1034.107666 mi/h (π÷180 is just a unit conversion) at the equator. Sound familiar?
Now, what really matters is ω - that 15°/h. This is half the angular speed of the hour hand on a clock. The hour hand on a clock goes around twice in a day, which works out to 30°/h. That’s not a movement we can easily perceive when viewed from altitudes like the one the Blue Marble photo was taken at, the perspective we have of the earth is very similar to the perspective we have of a clock. The angular speed is just slow enough we can’t perceive it.
Edit: unit errors in my math
FlyJunior172 t1_iubpdrp wrote
Reply to comment by notfrancisard in LPT Request: How to spot rental scams by Dauoa_Static
Don’t have the resources to do so, but threatening legal action was enough to get things moving on some of these issues.
FlyJunior172 t1_iubooug wrote
Reply to comment by notfrancisard in LPT Request: How to spot rental scams by Dauoa_Static
Failure to properly address maintenance requests in a timely manner. In my current apartment:
- I’ve had one plumbing leak cause my ceiling to come down, that took more than a month to get addressed.
- I’ve had another leak in the bathtub that spilled enough water on the floor to saturate beach towels for 72+ hours, that took a week and a half to address (all the while my apartment was technically uninhabitable).
- I can see daylight through the corner of my front door, the hole the daylight is coming through is big enough I have lizards coming in. That’s been an open and continuously reported issue since April.
- Leaky window reported in late August/early September, still hasn’t been looked at, let alone repaired.
- garbage disposal had no gasket in the drain from the sink (i.e. you could clearly see the blades), reported in April, not fixed until July
FlyJunior172 t1_iubnof0 wrote
Reply to comment by notfrancisard in LPT Request: How to spot rental scams by Dauoa_Static
I’ve had several landlords fail to fulfill their obligations. Problem is that the way most landlords fail to meet their obligations doesn’t show until after you move in.
FlyJunior172 t1_it16fyw wrote
Reply to comment by [deleted] in Why is it legal for us to have no representation? by throwawayobviousw
Because that would still put the federal government inside a state. You can’t put the seat of the federal government inside a state. That’s the whole reason DC exists in the first place.
They also tried something similar to what you suggest. Alexandria and Crystal City used to be in DC, but Virginia took the territory back when offered. Maryland declined the same offer.
The simple fact is that DC isn’t allowed to have a voting representative in Congress. If you don’t like that, move to Montgomery County - then you’ll get Jamie Raskin.
FlyJunior172 t1_it132oi wrote
Washington DC is a federal district with direct oversight of the federal government. The supremacy clause in the Constitution means that it cannot be a state (and therefore cannot have representation in Congress). DC was also never intended to be a city that people lived in. It was always meant to be the seat of the government, and only the seat of the government.
FlyJunior172 t1_iugy3pt wrote
Reply to comment by ShesOver9k in ELI5: if Earth rotates so fast, why does it always look still from outer space? by ShesOver9k
I wish there were a simpler way to explain where the big number comes from, but unfortunately there isn’t.
All the other methods I’ve learned for dealing with spinning things involve far more complicated math - usually matrices and reference frame conversions. This would be more of an ELI20, where v=rω is more like ELI8.