Recent content by starfish99

Thanks WannabeNewton

I know that Edwin Abbott more than 100 years ago wrote about a hypothetical universe with only two dimensions. I wonder if the force of gravity could exist in such a universe(please no general relativity). How would the force of 2 masses vary with distance? Could there be stable orbits and would...

Mfb is right that #4 is unintuitive. The martian pilot reasoned that Eartha's clock runs slower than his own clock during his journey. The pilot is surprised that Eartha's clock didn't have a lower reading than his own clock reading of 71 seconds. But if the Earth clock starts out with 203.8...

The fact that two rocket ships passing each other see the other ships clock run slow fascinates me. But what about total elapsed time? Suppose a person on Earth and a rocket ship on Mars 40,000,000 miles away are at rest relative to each other. They synchronize their clocks so that at t= 0...

Acceleration doesn't "cause" the Twin Paradox? In a recent review of a physics textbook, the reviewer is critical of the author of the book because the the author doesn't correct the persistent notion of many students that it is the acceleration of one of the twins that "causes"[reviewer's...

Sorry Robert1986 8X9X9X9 is the number of 5 digit numbers without a seven. 90 000 minus 8X9X9X9 is the number of 5 digit numbers with a seven. Thanx again

So a(4) can be any of eight numbers(1 thru 9) excepting 7 and a(3) a(2) a(1) and a(0) can be any of nine numbers (0 thru 9) excepting 7. The ans. is 90 000 minus 8x9x9x9. Thank you

Consecutive numbers without using a "7"? I tried to calculate the number of consecutive integers between 10,000 and 99,999 that do not use the number 7. I got part of the way there. There are 90,000 numbers(if you start with 10,000) and if you subtract 1/9 of 90,000 that will give you a total...

Thanks Gib Z

I am interested in calculating a a partial sum of harmonic series as an improper fraction. I added 1/2+1/3+1/4+1/5+1/6+1/7+1/8+1/9+1/10 with my calculator by finding a common denominator and got the fraction 6 999 840/3 628 800. It would take some time to do it for 1/2+1/3+...1/100. Is...

Suppose you had an electric mixer that stirs the water vigorously at room temp(20 degrees centigrade). The temp of the room suddenly drops 50 degrees. Now everything is at -30 degrees. Would the mixer eventually stop working because the ice forms and the blades of the mixer can't move or would...

There are many examples in nature of frozen moving water(frozen rivers, frozen streams,etc). How does the movement and turbulence of water affect its freezing point? If in a cold room kept at -1 degree centigrade we have two bowls:one bowl has one liter of water and the other has one liter of...

Comparison of charge to mass can be confusing. There is a positive and negative charge, but there is no positive and negative mass. In fact antimatter is composed of subatomic particles with opposite charges(negative protons and positive electrons) compared to conventional matter. The electron...

This may help: sin(a)+sin(b)=2(sin(.5)(a+b) X cos (.5)(a-b))

Kepler could have known the approximate distance from the Earth to the Sun( the ancient Greeks may have known this). However, I think he had no way of knowing the distance of the Sun to the other five known planets. So how could he have established his Law with only one point(Earth-Sun distance)?