Hacker News Reader

Comment by sam_goody | Hacker News Reader

Can someone please ELI5:

I was taught that all items fall at the same speed, due to the gravitational constant.

With these waves, does that mean that items will fall at ever so slightly differing speeds, as depending on the size of the wave there is a pull in the other direction, and the constant is slightly off?

And OT, but related: Since every item has a gravitational pull related to its mass, would a bigger item fall ever so slightly faster than a small one, as it is pulling itself to Earth in addition to Earth pulling it down.

View on HN

Gravitational waves warp space/time. so the distance between two points will be slightly longer/shorter.

No, gravitational waves do not affect the equivalence principle and do not change the gravitational constant. They are waves of change in the geometry of spacetime; freely falling objects show these spacetime geometry changes by changes in their relative motion.

Well in both your questions it depends on how you define speed. It is commonly understood to be the first derivative of position, or the quotient of distance divided by a time-span. But how do you define and measure distance and time-spans? Which reference frame do you use?

Also, the things falling in a vacuum at the same speed thing is a common misconception. The two arguments usually are that the mass of one body can be canceled out in both equations or that splitting a body into two won't make its halves fall slower.

To answer the question: Given all bodies have the same size, a constant distance to and mass of the reference body (usually earth) and everything starting at rest with no relative speed heavy and light bodies do experience the same acceleration, but a heavy body will collide sooner than a light body. Did it "fall faster"?

> heavy and light bodies do experience the same acceleration, but a heavy body will collide sooner than a light body.

I still don't understand, why would the heavy body collide sooner if they have the same acceleration (and starting at rest)?

Reply on news.ycombinator.com