This may have been covered and I just missed it or maybe it wasn't covered. Is the contraption essentially weightless as soon as it is released or does it need to accelerate before the effects of gravity are negated?

 

You shouldn't be reading this forum - sooner or later you're gonna laugh, and that sore head of yours is gonna hurt. Don't remember if you had any sore ribs, but if you did, they're gonna hurt too ...

 

Let's get back to the premise - Bubba is on the scale, and it shows 200lb. Then, a mechanism (similar to the one that releases the cork) suddenly releases Bubba and his scale (which is reading 200 lb, remember), which puts him - and the scale - into this supposed free fall. At that point in time, Bubba is sitting on a scale that says 200 lb. If it then changes to zero, what causes it to change?

If, while waiting to land, Bubba becomes bored, and decides to pass the time by juggling, can he actually toss a ball from one hand to the other? If he becomes bored with juggling, and decides to shoot one of the *****, will the bullet even leave the barrel?

As for the astronauts, as I've already mentioned, their gravitational force (weight) is canceled by their centrepital force.

 

I have to say the best question asked yet is, if in the space shuttle in a glob of water a cork is inserted which way will it pop out? I guess the answer is it will not. seems to make sense, but the bucket question just throws me. Great question.

 

That's a funny question alright. The only thing "containing" the water is its own surface, which is under tension, due to molecular forces. An attempt to push a cork into the blob would only result in the blob moving away from the cork. I suppose you could attempt to hold the blob with your other hand, but then the blob would merely distort in some other direction, resisting the insertion of the cork.

By the way, both the cork and the blob have weight.

 

We are getting further and further from the original cork question, but what the heck…

The mass of an object refers to the amount of matter that is contained by the object; the weight of an object is the force of gravity acting upon that object. In other words, mass is related to "how much stuff is there" and weight is related to the pull of the Earth (or any other planet) upon that stuff. Mass remains constant no matter where in the universe that object is located. Mass is constant and is never altered by location, the pull of gravity, speed or even the existence of other forces. For example, a 2-kg object will have a mass of 2 kg whether it is located on Earth, on the moon, or on Jupiter; its mass will be 2 kg whether it is moving or not. On the other hand, weight is subjective and will vary according to where in the universe the object is. Weight depends completely upon which planet is exerting the force and the distance the object is from the planet. As mentioned earlier, Poor old Bubba weighs 200 pounds on the Earth, 33 pounds on the moon, and a few ounces on an asteroid.

The force we typically interpret as weight is merely the upwards force negating the gravitational acceleration.

So what is “freefall”. Freefall is a condition created when an object is moving with a speed and direction equal to gravity. The Space Shuttle achieves this state through orbital velocity and the bucket of water creates the condition by falling unsupported through the air toward the earth.

For those disbeliveers, you can prove weightlessness to yourself by this simple experiment. Poke a hole in the side of a plastic bottle. Cover the hole with your finger while you fill the bottle with water. Uncover the hole. What do you think is pushing out the water?

Now, hold the bottle up high and let go. Why did the water stop pushing out?

Repeat as necessary until you understand weightlessness…



Here is a link explaining why the scale would read zero when Bubba and the scale were in freefall. (third paragraph uses this actual example)

http://science.howstuffworks.com/weightlessness1.htm

 

The main point I have been trying to make, is to not let pre-conceptions cloud judgement. Statements such as "objects in free-fall are weightless; those objects are in free-fall, and therefore are weightless" are incomplete and misleading. If they are taken at face value as the basis of an argument, other statements derived from them are also incomplete and misleading.

First, this free-fall business. I think the wording is what is causing confusion. Objects in free-fall are apparently weightless, because their weight is not measureable. That is not to say they are weightless - everything that has mass and is exposed to gravity has weight, for that is the definition. And, speaking of definitions, objects are considered to be in free-fall if the only force acting on them is that of gravity. Just saying that an object is in free-fall does not make other forces disappear. On the contrary, if other forces are present, and acting on an object, then it is not in free-fall.

That's what I was trying to demonstrate with Bubba sitting on a scale that read 200lb. Sure, once he and the scale are entered into a free-fall state, the scale will read zero. But, in order for the scale to get from 200 to zero, a force had to be applied. That force came from the conversion of energy stored in the springs of the scale. If you let the cart pull the horse, and say that no other forces are present, then that means that the scale would remain at 200, since no force exists to cause it to change. So, technically, during the time it takes for the scale to change to zero, there is another force (besides gravity) that is acting upon Bubba and his scale, and during that time they are not in free-fall.

Before the bucket and cork are dropped, there exists a pressure differential within the water, which causes a bouyant force upon the cork (in the opposite direction of gravity). When the bucket is dropped, the differential will tend to disappear, but not instantaneously. During the time the pressure is changing, there still exists a bouyancy force on the cork, that is causing it to move in the opposite direction of gravity, and will continue to do so until the pressure differential is removed. If this happens before the bucket lands, then the cork could remain suspended at some point within the water, above the bottom of the bucket, and below the surface of the water.

Note that I said "could", and not "would". There are too many variables that separate this hypothetical situation from the real world.

 

Sigma your own link states in paragraph 3:
"Weightlessness is more correctly termed microgravity. You are not actually weightless, because the Earth's gravity is holding you and everything in the shuttle in orbit. "

Now are you arguing FOR or Against the existence of weighlessness.

From your own post:
'The mass of an object refers to the amount of matter that is contained by the object; the weight of an object is the force of gravity acting upon that object. '

The mass remains constant, the force of gravity is constant (ok it varies with distance but over the short distance we are talking give me that). Therefore weight never ceases to exist. If weight ceased then you would stop falling. Either your mass went to zero or the force of gravity did.

In free fall, you APPEAR weigtless relative to everything else falling with you. So you still have weight, it just cannot be measured by conventional means.

Still don't believe it, do a vector analysis of an object in orbit. For you to be truely weightless the vector summ of all forces acting on your body must equal zero. First you have a vector toward the earth (gravity), second you have a vector 90 degrees to gravity in the direction you are orbiting. Those two vector sum up to put you at a point further in orbit at the same distance. The vector sum does not equate to zero and there is no vector in the opposite direction to gravity.

 

There is no "pressure differential" in the water when it is at rest and experienceing weight. The only reason the cork floats is because cubic-inch for cubic-inch, the cork is lighter than the water. Since it displaces a certain amount of water, the water level increases slightly, which gravity is trying to pull back down. The "weight" of the water is trying to expel the cork. It's called displacement, it's what keeps steel ships floating.

Once there is no "weight" in free-fall, there is no force pulling the water back down into the bucket, so the cork woudln't move. If there is any electro-static or other strong or weak forces acting on the cork squeezing it out of the water, it won't move to the top of the bucket, but possibly the closest surface (bottom?)

Anyway, this is getting long and drawn out, and a couple of people continue to argue finer and finer points, but the entire thing is getting blown out of proportion.

I was taught "weight" exists in a gravity field, when the object is NOT MOVING. If it's in free-fall, it has no weight. Mass on the other hand doesn't change regardless of in a gravity field, or not, moving, or not.

Using that definition of "weight", there is no weight in free-fall, so the only thing causing the cork to float (or even begin to move) is removed.

Again, the semantics of the word "weight" is what's screwing everyone up, I think.

By the way, I don't think the Apollo astronauts noticed a difference between being in orbit about the Earth, and traving to/from the moon (free-fall vs. true weightless).

I still don't buy that an object in free-fall still "weighs" something. I think someone, somewhere, has gotten mass and weight confused.

 

Sigma - you have pretty long posts for someone who has to type with a stick in their mouth. Can you do Peter Frampton impressions with your electronic voice box?

 

Arguing for the existence of weightlessness, of course, but we have gotten too far off the original topic for it to be meaningful. Lets just agree to disagree

 

Where did that come from

 

As krewat stated, the pressure differential/bouyancy is just the weight difference between the cork and the same volume of water. Gravity is always applying a force of 32 ft/sec^2 on objects near Earth's surface. Assuming the bucket is stationary, whatever is holding up the bucket is exerting exactly the same amount of force as gravity but in the opposite direction. When the bucket is released, the force opposing the gravity instantly disappears and the bucket instantantly becomes weightless. It does take time to reach a certain velocity, but that has no affect on the bucket's or the cork's weight. At 0 sec (the instant the bucket is released) it's weightless. After 1 sec, the bucket is traveling 32 ft/sec and is weightless. After 2 sec, it's traveling 64 ft/sec and it's still weightless. Weightlessness is not a function of velocity, it's about how much force is being applied to oppose gravity. At least that's how my physics homies 'splained it.

I suppose you could argue that in the real world how do you instantaneously remove the force holding the bucket. In reality, the handle quickly slips out of your fingers and quickly, but gradually removes the opposing force. If the cork were released before the handle had completely slipped away, it would begin to float.

 

Figured you were Steven Hawking.

 

Okay, I told myself I wasn't going to reply to any of these physics quizes. But I couldn't resist.

Since you made us strain on brains, I'm gonna call it 'void', due to a technicalility.


With the wording "...a cork held by a clamp attachment at the bottom of a bucket of water." one could interpret it as the cork is clamped at the base on the outside of the bucket. I know you meant that "...a cork held by a clamp attachment in the bottom of a bucket of water." The key words are "at" versus "in". That just leaves the whole problem up for interpretation now with different correct answers.

Now, to the rest of the problem:

Going with my original line of thinking, that the cork is clamped outside at the base of the bucket. "If the clamp is designed to release the cork at the same instant the bucket is dropped off the side of a sky scrapper, what will happen to the cork during the fall?"

Right here, the bucket and cork are released simultaneously and the clamp releases both items.

"Will it float to the top of the bucket normally, slower than normal, faster than normal, or not at all?"

Assume that there is no air resistance to slow the bucket down."

Going with my original line of thinking......using that technicality.....The cork will appear to float to the top of the bucket faster than normal. I say that because it is on the outside of the bucket. And there is no air resistance on the bucket, but since that same air resistance comment is not applied to the cork, the cork will feel air resistance. Thus the bucket drops faster than normal, because of no air resistance, but the cork "appears to float" because it is getting the effects of air resistance and is not in the bucket so it is not surrounded by water. The only effects on the cork would be gravity and air resistance as the cork floats on air towards the earth.

So, how's that for thinking outside the box? Do I win an Obscure Thinking Award? Am I just warped, or what?