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Author Topic:   Using your common sense to solve a physics problem.
Rrhain
Member
Posts: 6351
From: San Diego, CA, USA
Joined: 05-03-2003


Message 57 of 188 (144368)
09-24-2004 3:22 AM
Reply to: Message 5 by Percy
09-22-2004 5:39 PM


Re: Bump
Percy writes:
quote:
Perhaps you could start with a simpler question, like, "Is there sufficient information to solve the problem? Explain why or why not."
This reminds me of a Foxtrot cartoon that I have since used as a training for new tech support staff. We've all seen this kind of word problem setup:
A train leaves Station A at 10:00 am and arrives at Station B, 180 miles away, at 2:00 pm.
Now the question I have is: What do we need to assume in order to determine the average speed of the train?
You see, those of us who have done a slew of these problems will look at the setup, see the appropriate signals (180 miles, 4 hours) and jump to the perfectly sensible answer (divide the miles by the hours and come up with 45 mph.)
But what do you do when the person on the other end of the phone says, "It still doesn't work"? The most obvious solution is quite often correct, but every now and then you find you're ignoring something that hasn't been directly stated:
Just because the stations are 180 miles apart doesn't mean the track between them is 180 miles long. Perhaps the track is a Euclidean straight line that tunnels through the earth and thus ignores the curvature of the earth. Perhaps the track takes the scenic route and zig-zags back and forth along the way. Perhaps the train went the other way, a journey of about 23,820 miles. And what if it took the scenic route on that journey, too?
Are the stations in the same time zone? For that matter, it was never explicitly stated that the train arrived the same day. We're assuming the clocks are working. It might always be "2:00 pm" at Station B. When we said "10:00 am" and "2:00 pm," did that mean clocks at the station or clocks we're carrying with us? If we're carrying the clocks, shouldn't we take relativistic effects into account?
See, this is why anecdote is not evidence. The seemingly simplest of questions require tremendous amounts of control in order to make sure that we have even a hope of saying we understand what's going on. The idea that a person can "common sense" his way through something as complicated as the diversification of life is ridiculous. You can't "common sense" your way through something as simplistic as "How fast was the car moving?"
As someone more erudite once said, "Common sense is neither common nor sensible."

Rrhain
WWJD? JWRTFM!

This message is a reply to:
 Message 5 by Percy, posted 09-22-2004 5:39 PM Percy has not replied

Rrhain
Member
Posts: 6351
From: San Diego, CA, USA
Joined: 05-03-2003


Message 99 of 188 (144579)
09-25-2004 12:03 AM
Reply to: Message 62 by Ooook!
09-24-2004 5:39 AM


Re: Another example of common sense...
Ooook! writes:
quote:
On a slightly different note : Does anyone have any non-physics/maths problems that could be set ?
Two common, seven-letter words, each of which has eight words within. One is different from another and therein lies the answer.

Rrhain
WWJD? JWRTFM!

This message is a reply to:
 Message 62 by Ooook!, posted 09-24-2004 5:39 AM Ooook! has replied

Replies to this message:
 Message 100 by crashfrog, posted 09-25-2004 12:14 AM Rrhain has replied
 Message 107 by Ooook!, posted 09-25-2004 5:23 AM Rrhain has replied

Rrhain
Member
Posts: 6351
From: San Diego, CA, USA
Joined: 05-03-2003


Message 101 of 188 (144582)
09-25-2004 12:25 AM
Reply to: Message 100 by crashfrog
09-25-2004 12:14 AM


crashfrog responds to me:
quote:
Heights and weights?
Clever, but not quite what I had in mind. That is, your words do contain the word "eight," but I said "eight words," and "eight" is singular in that it is only one word. When I said "eight words," I mean if you take the letters of the word, read them left to right, without re-ordering, you'd find eight words:
He, height, eight, eights...that's only four.

Rrhain
WWJD? JWRTFM!

This message is a reply to:
 Message 100 by crashfrog, posted 09-25-2004 12:14 AM crashfrog has replied

Replies to this message:
 Message 102 by crashfrog, posted 09-25-2004 12:29 AM Rrhain has replied

Rrhain
Member
Posts: 6351
From: San Diego, CA, USA
Joined: 05-03-2003


Message 103 of 188 (144585)
09-25-2004 12:44 AM
Reply to: Message 102 by crashfrog
09-25-2004 12:29 AM


crashfrog responds to me:
quote:
Now that I understand your problem, it's too hard for me.
No, it isn't.
Like the original physics question, you have all the information you need to solve the puzzle.
And no, I don't mean doing something like looking up words in a dictionary. Look at the puzzle again:
Two common, seven-letter words, each of which has eight words within. One is different from another and therein lies the answer.

Rrhain
WWJD? JWRTFM!

This message is a reply to:
 Message 102 by crashfrog, posted 09-25-2004 12:29 AM crashfrog has not replied

Replies to this message:
 Message 104 by jar, posted 09-25-2004 12:54 AM Rrhain has replied

Rrhain
Member
Posts: 6351
From: San Diego, CA, USA
Joined: 05-03-2003


Message 105 of 188 (144589)
09-25-2004 1:16 AM
Reply to: Message 104 by jar
09-25-2004 12:54 AM


Check your spelling, jar. "Ether" does not appear in "another."

Rrhain
WWJD? JWRTFM!

This message is a reply to:
 Message 104 by jar, posted 09-25-2004 12:54 AM jar has replied

Replies to this message:
 Message 109 by jar, posted 09-25-2004 9:54 AM Rrhain has not replied

Rrhain
Member
Posts: 6351
From: San Diego, CA, USA
Joined: 05-03-2003


Message 115 of 188 (144692)
09-25-2004 4:49 PM
Reply to: Message 107 by Ooook!
09-25-2004 5:23 AM


Ooook! writes:
quote:
I blooming hate word games too
Well, make up your mind!
quote:
Actually what I had in mind would be something from other sciences like chemistry, or biology.
OK:
Suppose we have a single-gene, single-trait characteristic in a diploid organism such that there is one dominant allele and one recessive allele. To put it in a classic Mendelian sense, there is A and a and that's it.
Suppose that the occurrence of the recessive phenotype (that is, people who actually express the recessive characteristic or, in Mendelian genetics, aa) is one in a thousand.
Suppose that we can control breeding such that those who do express the recessive characteritic do not have children.
How many generations would it take to reduce the expression of the recessive characteristic from one in a thousand to one in a million?
Some hints!
Don't get bogged down in individuals. Assume there is a large enough population that everybody can find a mate.
Other than the prohibition on those who are aa reproducing, all other mating is random. Thus, all those who are AA and Aa will mate, but they do not know the genetic makeup of the other.
Think about dividing the gene population. For example, let p be the ratio of A genes in the population and let q be the population of a genes. Thus, p + q = 1. What other equation can we derive? And what is it we're trying to do to that other equation?

Rrhain
WWJD? JWRTFM!

This message is a reply to:
 Message 107 by Ooook!, posted 09-25-2004 5:23 AM Ooook! has replied

Replies to this message:
 Message 120 by Ooook!, posted 09-26-2004 5:11 PM Rrhain has not replied

Rrhain
Member
Posts: 6351
From: San Diego, CA, USA
Joined: 05-03-2003


Message 149 of 188 (145559)
09-29-2004 4:02 AM
Reply to: Message 137 by riVeRraT
09-28-2004 10:13 AM


Re: Nonresponse
riVeRraT writes:
quote:
And why would I not have a better understanding of pyhsics than a scientist who maybe didn't do well in physics?
Because you cannot get that far and not be good at it. I'm not saying that you need to have formal training in order to be good, but you cannot advance that far without being good. It is something that you need to work at every day and that's what formal training provides you.
quote:
Wouldn't you agree that some people can see whats going on better than others?
Yes, but who is more likely to be better at it: Someone who has spent the past eight years working on a subject every day, being taught from others who have spent the past few decades working on the subject every day? Or someone with only a passing interest who doesn't deal with the subject very often?
quote:
The reason why you guys are getting confused with what I said is that you think common sense and education are the same, its not.
No, that's our argument to you. You are the one claiming that common sense is equivalent to education and it isn't. You are the one claiming you can "common sense" your way through a problem that PhDs spend their lives working on.
quote:
Ones common sense can be greater than anothers regardless of education.
Of course.
But all the common sense in the world won't help you without an education to teach you how to use it.
quote:
That doesn't make me right or wrong. I came up with a common sense theory, and looked to prove it through those who are educated.
So why is it you won't listen to them when they tell you it is nonsense?

Rrhain
WWJD? JWRTFM!

This message is a reply to:
 Message 137 by riVeRraT, posted 09-28-2004 10:13 AM riVeRraT has replied

Replies to this message:
 Message 153 by riVeRraT, posted 09-29-2004 7:08 AM Rrhain has replied

Rrhain
Member
Posts: 6351
From: San Diego, CA, USA
Joined: 05-03-2003


Message 150 of 188 (145560)
09-29-2004 4:09 AM
Reply to: Message 145 by riVeRraT
09-28-2004 7:18 PM


Re: Nonresponse
riVeRraT writes:
quote:
In a global flood, things would be much different, and the water may not have anywhere to go.
Then why isn't the earth still flooded? After all, the entire earth was flooded and there was nowhere for the water to go.
So where did it go?

Rrhain
WWJD? JWRTFM!

This message is a reply to:
 Message 145 by riVeRraT, posted 09-28-2004 7:18 PM riVeRraT has replied

Replies to this message:
 Message 154 by riVeRraT, posted 09-29-2004 7:08 AM Rrhain has replied

Rrhain
Member
Posts: 6351
From: San Diego, CA, USA
Joined: 05-03-2003


Message 169 of 188 (145915)
09-30-2004 7:45 AM
Reply to: Message 153 by riVeRraT
09-29-2004 7:08 AM


Re: Nonresponse
riVeRraT responds to me:
quote:
quote:
So why is it you won't listen to them when they tell you it is nonsense?
Because they are just telling me, not proving it.
Did you try the experimet I suggested?
If not, then the problem is not that it hasn't been proven. It's that you've been too stubborn to notice.
This is not the first time I have asked you if you tried the experiment.
quote:
Common sense can prevail in a lot of situations vs. education.
No, it can't. That's why we have been asking you various questions that are fairly simplistic in the fields in which they come up but are incredibly difficult to determine if you're just trying to "common sense" your way through it.
quote:
But I this happen mostly in the medical field.
Incorrect. The medical field is just as technical as any hard science. Do you seriously think that doctors aren't trained in diagnostic methods?
Question: If your knee isn't hurting, is it actually undamaged?

Rrhain
WWJD? JWRTFM!

This message is a reply to:
 Message 153 by riVeRraT, posted 09-29-2004 7:08 AM riVeRraT has replied

Replies to this message:
 Message 174 by riVeRraT, posted 09-30-2004 8:40 AM Rrhain has replied

Rrhain
Member
Posts: 6351
From: San Diego, CA, USA
Joined: 05-03-2003


Message 170 of 188 (145916)
09-30-2004 7:49 AM
Reply to: Message 154 by riVeRraT
09-29-2004 7:08 AM


Re: Nonresponse
riVeRraT responds to me:
quote:
IT stop rhaining.
But it remained flooded for five months after it stopped.
Did you try the experiment I suggested? I'm simply asking you to keep the object submerged for 20 minutes. Eventually you need to figure out a way to keep it submerged for 150 days.
If you can flood the entire earth such that every square inch of land is submerged at least 20 feet and remains submerged at least 20 feet for five months, why isn't the earth flooded right now?
The problem isn't getting the water to the land. It's keeping it there.

Rrhain
WWJD? JWRTFM!

This message is a reply to:
 Message 154 by riVeRraT, posted 09-29-2004 7:08 AM riVeRraT has replied

Replies to this message:
 Message 175 by riVeRraT, posted 09-30-2004 8:41 AM Rrhain has replied

Rrhain
Member
Posts: 6351
From: San Diego, CA, USA
Joined: 05-03-2003


Message 171 of 188 (145918)
09-30-2004 8:08 AM
Reply to: Message 167 by riVeRraT
09-30-2004 6:55 AM


Re: Solving it using common sense.
riVeRraT writes:
quote:
Ok, I haven't had anytime to devote to learning physics
See, we have. I still remember the professor's comment during one of them: Everything will be fine so long as you don't eat the radioactive source.
You see, while there was a danger from the radiation (and we had to wear the little clips that got developed in order to determine if there was an overexposure) that might cause an elevated cancer risk in 30 or 40 years, the bigger problem was that the source was extremely toxic and would kill you right away.
When was the last time you were in a physics lab running an experiment?
Did you try the experiment I suggested?
quote:
First off, I fully understand the implimications of the problems without knowing pyhsics.
Obviously not because you think the problem is one of physics when it's actually one of topology.
quote:
I would also be able to solve it in the real world.
So why haven't you?
Have you tried the experiment I suggested?
quote:
You have the force of the car moving, plus the force of the slope, minus the friction of the skid. Its pretty simple.
And yet you got it wrong and had to be shown how to solve it.
Do you stick with the door you originally chose or do you switch? We're still waiting for an answer.
quote:
IF I had to figure out if this guy was speeding or not using my common sense, I would take a car of the same, using the same tires, and do some skid tests at the seen of the accident. After a couple of slides
While the brute force method does work to solve many problems, it isn't always feasible. That's why you develop methods that will let you know what the answer is without having to completely recreate the scenario. Take evolution, for example. It isn't like we have a spare planet lying around that can be seeded with appropriate organics and left to simmer for 4.5 billion years. How do you plan to brute force your way through a process that takes longer than you could possibly live?
quote:
I just haven't figured out really how to apply the coefficient of friction to the formula to calculate the speed.
Why not? It's crystal clear to anybody who's had basic physics training.
quote:
So my question is, if I currently do not understand the numbers, does this mean I cannot see what is going on using my common sense?
Yes.
Oh, you might have a decent understanding of the broad process, but the devil, as they say, is in the details.

Rrhain
WWJD? JWRTFM!

This message is a reply to:
 Message 167 by riVeRraT, posted 09-30-2004 6:55 AM riVeRraT has replied

Replies to this message:
 Message 176 by riVeRraT, posted 09-30-2004 8:43 AM Rrhain has not replied

Rrhain
Member
Posts: 6351
From: San Diego, CA, USA
Joined: 05-03-2003


Message 177 of 188 (145943)
09-30-2004 9:18 AM
Reply to: Message 174 by riVeRraT
09-30-2004 8:40 AM


Re: Nonresponse
riVeRraT responds to me:
quote:
Would you stop explaining the incredibly obvious to me?
No.
It is incredibly obvious that you do not understand the incredibly obvious.
Do you keep the door you originally chose or do you switch?

Rrhain
WWJD? JWRTFM!

This message is a reply to:
 Message 174 by riVeRraT, posted 09-30-2004 8:40 AM riVeRraT has replied

Replies to this message:
 Message 182 by riVeRraT, posted 09-30-2004 9:28 PM Rrhain has not replied

Rrhain
Member
Posts: 6351
From: San Diego, CA, USA
Joined: 05-03-2003


Message 179 of 188 (145945)
09-30-2004 9:20 AM
Reply to: Message 175 by riVeRraT
09-30-2004 8:41 AM


Re: Nonresponse
riVeRraT responds to me:
quote:
quote:
But it remained flooded for five months after it stopped.
Care to explain how?
Nice try. That's our question to you.
You're the one claiming there was a flood. You're the one using the Bible as a reference.
Since the Bible claims the flood lasted for 150 days after the 40 days of rain, then it is your job to explain how the earth remain flooded for five months after it stopped.
quote:
Because as far as I know, when it stops raining, the water would drain away rather fast.
Then it isn't flooded.
Why are you arguing for a flood when you agree that it can't flood?

Rrhain
WWJD? JWRTFM!

This message is a reply to:
 Message 175 by riVeRraT, posted 09-30-2004 8:41 AM riVeRraT has replied

Replies to this message:
 Message 184 by riVeRraT, posted 09-30-2004 9:32 PM Rrhain has not replied

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