Question for the Science Guys (Jewett, Dr. Dave)

I'm just a ball banging non-science guy but gravity has a more immediate effect on a slow moving horizontal object than on a fast moving horizontal object and gravity is what causes balls to roll off on a table that isn't level, like the one in my basement.

If a ballplayer throws a ball at 5 mph it will drop faster than a ball thrown at 100 mph.
 
jay helfert said:
If any of you watched the old Dennis Miller show that was on HBO for years, you may have noticed in the opening sequence six balls that looked like little "Earths" going into six pockets on a pool table. The song "Everybody Wants To Rule The World" was playing in the background while this shot was being made.

Well, I made that shot for Dennis. It was done by using six cue balls painted to look like planet Earth. And it was made on a movie prop "pool table". This table had a plywood surface covered with plain green cloth. To say it rolled off is a massive understatement. The balls literally rolled everywhere in every direction.

I tried the shot a few times and told them it was nearly impossible to make this shot. Balls were rolling everywhere. I said there may be one way for me to do it. I have to shoot REAL hard! That way there is little, if any, roll off before they reach the pockets. The Director said go ahead and try it. I shot it six times with full force and twice I made all six balls/Earths. And I mean I hit it really hard!

Just like that, we were done with my segment. When it aired on TV, they slowed down the film speed considerably, so you could see the balls rolling into the holes. Ah, the wonders of Hollywood! Of course, they substituted Dennis for me, and made it look like he made the shot. I enjoyed hanging out with Dennis that day. He's a cool guy and very bright.
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No kidding? Great stuff Jay! I actually had no intention of ever watching that show, but that opening caught my eye one night, so I watched it a few times.
 
jay helfert said:
Bottom line, if a ball rolls off by one inch, you better get your table re-leveled. That's a bad roll off you have there. :D
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Well, yes, but, have you never found yourself playing in a situation where you were on a tilted table that couldn't be leveled before play continued? Sometimes you have to play with the table you have and not the table you want.

As I mentioned above, I used to play on a table where the side pocket might swallow anything close to it. A spot shot played at medium-slow speed had to be aimed full-ball to be made from the right side and thin-ball to be made from the left side. One of the things I learned on that table was that for some nearly straight shots with a lot of roll, you could aim normally and the cue ball would roll over some to the right, cutting the object ball to the left and then the object ball would roll to the right to go into the pocket. Or, you could shoot hard.

I think it is not uncommon for a table to roll off an inch when slow-rolling the cue ball to a ball in a far pocket, at least for one direction on the table.
 
alstl said:
I'm just a ball banging non-science guy but gravity has a more immediate effect on a slow moving horizontal object than on a fast moving horizontal object and gravity is what causes balls to roll off on a table that isn't level, like the one in my basement.

If a ballplayer throws a ball at 5 mph it will drop faster than a ball thrown at 100 mph.
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I'm sure someone else can explain this better, but the two balls are actually effected by gravity the same. You notice the effect within a shorter distance from the origin (ballplayer's hand), with the 5 mph toss, but they are actually falling at the same rate. So for the sake of explanation, pretend that nothing gets in the way of either toss, and you measure the distance that each ball travels. The 5 mph toss will travel 5 feet and the 100 mph toss will travel 80 feet (both made up numbers), but they will both take the same amount of time to travel their respective distances, and they will hit the ground at the same time.
 
Physics class....always good for a nap or two.

Vectors, friction coeficients, angle of incidence, gravity, force, Newton's laws of motion. Just think we could all be physics professors by now!

Physics and the beauty of Pool 101

td
 
In practical terms it is often much better to think of "the accelleration due to gravity" than the "force of gravity" ... at least here on the surface of the earth where we mostly live and play ... it gets that time concept firmly in place.

Dave
 
spoons said:
I'm sure someone else can explain this better, but the two balls are actually effected by gravity the same. You notice the effect within a shorter distance from the origin (ballplayer's hand), with the 5 mph toss, but they are actually falling at the same rate. So for the sake of explanation, pretend that nothing gets in the way of either toss, and you measure the distance that each ball travels. The 5 mph toss will travel 5 feet and the 100 mph toss will travel 80 feet (both made up numbers), but they will both take the same amount of time to travel their respective distances, and they will hit the ground at the same time.
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This is 100% correct. Gravity is constant. The formula for the rate of gravity remains unchanged by horizontal force.
 
Jude Rosenstock said:
This is 100% correct. Gravity is constant. The formula for the rate of gravity remains unchanged by horizontal force.
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True sort of, but a moving object can resist gravity. The moon doesn't fall to Earth.
 
alstl said:
True sort of, but a moving object can resist gravity. The moon doesn't fall to Earth.
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Well, we're talking about Earth's gravitational pull on objects in its atmosphere. The moon isn't in the Earth's atmosphere and has a few other variables in place. In fact, the moon is moving AWAY from Earth at a rate of 38 milimeters per year.
 
DaveK said:
Nothing resists gravity. The moon does fall to earth, thankfully it never gets here 'cause it's "in orbit". Newtons outstanding demonstration shows this better than anything :

http://www.astronautix.com/lvs/newannon.htm

Dave
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Actually, it's quite the opposite. The moon moves away from Earth at a rate of 38 milimeters per year. So, in about a trillion years, that piece o' cheese will practically be invisible. Boy, I can't wait to see that!
 
Jude Rosenstock said:
Well, we're talking about Earth's gravitational pull on objects in its atmosphere. The moon isn't in the Earth's atmosphere and has a few other variables in place. In fact, the moon is moving AWAY from Earth at a rate of 38 milimeters per year.
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The moon is within the Earth's gravitational force, if not its atmosphere. I'm poorly educated but isn't it a time thing, just like the ball on the pool table? The Earth isn't flat, it is round. If you apply enough force to a "horizontal" object it will continue on a line which will carry it out of the Earth's atmosphere because it is traveling at such a high rate of speed that the atmosphere doesn't have enough time to pull it back.

At least that makes sense inside my brain.
 
alstl said:
The moon is within the Earth's gravitational force, if not its atmosphere. I'm poorly educated but isn't it a time thing, just like the ball on the pool table? The Earth isn't flat, it is round. If you apply enough force to a "horizontal" object it will continue on a line which will carry it out of the Earth's atmosphere because it is traveling at such a high rate of speed that the atmosphere doesn't have enough time to pull it back.

At least that makes sense inside my brain.
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The moon is in fact falling toward earth with a constant acceleration due to gravity as all objects in orbit are. The orbit of the moon is increasing in diameter a very tiny amount each year due to it's momentum. The moon will eventually slow to the point where it's orbit will begin to decay due to the universal forces of gravity and friction. When this happens, the moon will begin to move toward the earth instead of away. The resulting tidal effects between the moon and the earth will pull the moon apart, assuming the sun has not gone nova first and consumed both the moon and the earth.
 
DoubleA said:
The moon is in fact falling toward earth with a constant acceleration due to gravity as all objects in orbit are. The orbit of the moon is increasing in diameter a very tiny amount each year due to it's momentum. The moon will eventually slow to the point where it's orbit will begin to decay due to the universal forces of gravity and friction. When this happens, the moon will begin to move toward the earth instead of away. The resulting tidal effects between the moon and the earth will pull the moon apart, assuming the sun has not gone nova first and consumed both the moon and the earth.
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Then what, it all gets blasted out of the other end of a black hole and starts over again?
 
jason said:
There is another factor that hasn't been mentioned. Not all balls are prefectly round or weighted evenly. This could also cause the ball to roll off. And then there is the lint or chalk...but this never happens to JA!
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I agree. I am almost positive that the cheap balls that came with my "new table" accessory kit did not roll straight. I no pro player, but my game made a quantum leap IMMEDIATELY when I got my Super Pro Aramith set.

Tom
 
alstl said:
Then what, it all gets blasted out of the other end of a black hole and starts over again?
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LOL, no at that time it will become a ring of debris around the earth (think of a halo) in the same orbital plane as before it was destroyed. Not to worry though, all this should not take place until millions of years in the future.
 
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DoubleA said:
The moon is in fact falling toward earth with a constant acceleration due to gravity as all objects in orbit are. The orbit of the moon is increasing in diameter a very tiny amount each year due to it's momentum....
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It's actually gravity that's pulling the moon away - quite the trick from mother nature.

Jim
 
DoubleA said:
LOL, no at that time it will become a ring of debris around the earth (think of a halo) in the same orbital plane as before it was destroyed. Not to worry though, all this should not take place until millions of years in the future.
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I jog daily and lift weights at the gym. I might still be around. I just hope whatever piece of debris I'm on has room for a nine footer.
 
Jal said:
It's actually gravity that's pulling the moon away - quite the trick from mother nature.

Jim
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Yeah, I watch the Science Channel all the time. The moment they get into the physics of space & time, my brain hurts. I actually had to look up what the moon is doing and it's listed as moving away from the Earth at a rate of 38 mm per year. I can't say I understand it. That's what I found.

What's more, there are physicists that talk about "missing gravity". They claim gravitational force should be much much greater and attribute it to string theory (multiple dimensions) or something like that. I'm lost at that point and can only say that casual observations about space are only sometimes correct and usually that's just a coincidence.
 
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