Homework help - Models.

[Relative]

I am unsure of what a model actually is.

 

From what I have gathered , it would be a diagram with added maths , that all fits together.

 

 

I have tried an example and made a make shift model to see if this is what you mean.

 

 

 

Space is equal to 0,

0 is equal to constant.


0C+CE=EC

Zero is constant, add constant energy, equals an energy constant.

 

Would this be a simple model?

 

 

 

Or more on the lines of using Plank constants etc?

 

[swansont]

Models use well-defined parameters, and are often derived from established principles. "Space = 0" does not qualify. You are adding it to energy, which has units of energy. Unless you can somehow define "space" to have units of energy, the equation is trivially invalidated.

[Relative]

Models use well-defined parameters, and are often derived from established principles. "Space = 0" does not qualify. You are adding it to energy, which has units of energy. Unless you can somehow define "space" to have units of energy, the equation is trivially invalidated.

Ok , hmmm,

 

 

 

 

I thought space was full of EMR my mistake.

 

If I incorporated this into the model?

 

Would that be a more better model?

kh+xh=y?

[CaptainPanic]

A model is a mathematical description of a phenomenon that you have obseved in the real world.

 

I think your first problem is that you don't know what phenomenon you want to model:

 

Examples can be:

- The increase in energy of an object as it is heated by the sun.

- The trajectory of a tennisball after being served by a world-class tennis player.

- The increase of plankton mass in the oceans in springtime.

 

All those things are a function of time. But things don't always have to change in time:

- Find out which machine is the bottleneck in a car factory, and prevents an even higher production rate.

 

 

Generally, you first start off with a question, or something that you need to know. Then you look at how you can describe that using the formulas that you know from your scientific education - and often you need to combine those in a more complicated model. Sometimes you need to create your own correlation, because no formula exists yet.

Then, if you are lucky, you know all the variables, and can calculate your answer now. But often you need to look things up, or even take an educated guess for some variables.

[Ophiolite]

Most of your responses, Relative, have come from physicists, or those more interested in the harder sciences. In something like Earth science, for example the model can begin life as a verbal description: but it must be detailed, self consistent and well supported by observation. (The latter would be what had inspired the model in the first place.)

 

Later the model may well acquire a mathematical foundation, but in many instances this is superfluous when applying the model. For example,the theory of plate tectonics, based on several lines of evidence for sea floor spreading and subduction, was already generating new insights and explanations in the mid 60s. This was before Le Pinchon (or it might have been McKenzie and Parker) integrated the observations with the mathematics of rigid plates moving differentially on a sphere.

 

Thus I think of a model as a story about how we think something works. That story may be told in words, or maths, or a combination of the two.

[swansont]

I thought space was full of EMR my mistake.

 

kh+xh=y?

It is. But that's not what you had said or described.

 

what are all of the terms in your equation? How is it derived? Why should the equation work? You can't just write something down and assume it means anything.

[physica]

luckily I've just come back from a summer school completely devoted to mathematical modelling (final year physics student). What they told us is that a model follows 5 key steps:

• specify a purpose
• create the model
• do the maths
• interpret the results of the maths
• evaluate (do experiment)

If the experiment doesn't agree with your maths then revise the model. Mathematical modelling is not as easy as it sounds and loads of practice of the subject needs to be done in order to get a feel for mathematical modelling. The problem is that many people teaching themselves want to get stuck into the really interesting subjects that are counter intuitive and need mathematical modelling experience to tell you where you went wrong as opposed to everyday life experience. If we want to get a feel for modelling we have to start simple. A square mass sliding on a inclined plane is a good exercise:

 

Specify a purpose

find out the friction coefficient between the plane and the square mass

 

Create the model

This can be done by a simple force diagram. Summing up all the forces as vectors and equaling them to zero will mean that the mass isn't moving (make sure you define the axis in the way to make it easiest for your model). If you know how to properly define all the forces you will realise that some will depend on the angle of the inclined plane.

 

Do the maths

Simple algebraic manipulation of your model should give you a value of the friction coefficient based on a trigonometric function to the angle of the inclined plane (note that mass of the block isn't needed in this model but you should be able to mathematically prove why). Your units should also make sense.

 

interpret results

This is where we ask the question, what is the maths telling us about reality? For this model it's nothing profound. it's practically useful and because of it's practicality it's good for people to try in order to practice their modelling skills. This model tells us that if we can measure the maximum angle before the square mass starts to slip we can work out the friction coefficient.

 

Evaluate

This is where you do the experiment to obtain the reading

 

After this you repeat the cycle. You want to make sure that the reading you got was accurate and that your model was correct so you repeat the cycle with a slightly different purpose, different maths that incorporates the friction coefficient making some other measurement the subject and then evaluate. This is the scientific process. I urge you to try this process because this model is easy to evaluate at home. If you are not experienced you will go round in circles and expose your own shortcomings which is essential. The more abstract concepts like energy distribution, quantum mechanics and relativity are reserved for people who have proved themselves to be very good at this process. This is because it is more abstract and divorced from everyday experience.

 

I urge you to try this simple model. It is good fun and gives you a hands on feeling for the scientific method and modelling and increase your creativity with maths. You can private message me if you get stuck and need help or set up another thread in the homework help problem.

Edited August 28, 2014 by physica

[Relative]

It is. But that's not what you had said or described.

 

what are all of the terms in your equation? How is it derived? Why should the equation work? You can't just write something down and assume it means anything.

I thank you all for some great answers, that will take me a while to get my head around.

 

I am not really considering anything, it was just an example, trial and error , to try to get an idea of what a model is.

 

 

I used the speed of light, ,<C>, been a constant, <h>

 

space/darkness =zero , zero been a constant ,<h>

 

y=kx

 

k and x been direct proportional,

 

Y been light.

From what I have read, I only have to put k and x leaving the h out, because k and x already would be a constant ?

''If one variable is always the product of the other and a constant, the two are said to be directly proportional''

 

 

This.

[physica]

I am not really considering anything, it was just an example, trial and error , to try to get an idea of what a model is.

If you want to do this try the block sliding on an inclined plane model. It's simple and you can physically test it at home.

 

As for the rest of your last post it is complete gibberish. Do not waste anymore time on space and darkness equating to zero.

 

 

''If one variable is always the product of the other and a constant, the two are said to be directly proportional''

This is just maths. You do not have to understand modelling for this.

[Ophiolite]

Relative, you last post is not at all clear. What is h, what are the dimensions of y, k and x, what are y, k and x? k or x appear to be variables, as you have written the equation. Your last sentence, a quote, is correct, but I am not convinced you understand what it could mean in the context of a model.

[Relative]

If you want to do this try the block sliding on an inclined plane model. It's simple and you can physically test it at home.

 

As for the rest of your last post it is complete gibberish. Do not waste anymore time on space and darkness equating to zero.

 

 

This is just maths. You do not have to understand modelling for this.

I do not think I understand modelling, I will look at your block sliding.

 

I thought EMR was a product of the Sun?

 

And the visual universe directly proportional to the Sun.

 

Light making the visual .

 

Is the light not directly proportional to the Suns energy output?

 

And if space and darkness is not zero what is it?

 

Please explain where my model is flawed, this will help me learn modelling.

Relative, you last post is not at all clear. What is h, what are the dimensions of y, k and x, what are y, k and x? k or x appear to be variables, as you have written the equation. Your last sentence, a quote, is correct, but I am not convinced you understand what it could mean in the context of a model.

Y is light, X is the Sun/energy/light, k is darkness and the volume of space we can see.

Y is visual universe maybe , unsure.

oh sorry and h is plank constant.

My homework is to make a new model.

[Ophiolite]

Start with something simple. And where the terms have genuine physical meaning, not the nonsense about dark and light that you have been advised to drop by several people, several times.

 

I'm not even sure you should even be starting with models at this point, given the random nature of your current misunderstanding. Perhaps other, more knowledgeable than I can comment on whether this site is worth pursuing, or recommend a better one. http://www.physicsclassroom.com/

[swansont]

I do not think I understand modelling, I will look at your block sliding.

 

I thought EMR was a product of the Sun?

 

And the visual universe directly proportional to the Sun.

 

 

How can the visual universe be directly proportional to the sun? That makes absolutely no sense. Nothing there is something that is quantified or is a property recognized in physics.

[imatfaal]

!

Moderator Note

 

Relative

 

If you want guidance in creating physical models and obtaining predictions from them then we MUST use a simple example. I would suggest a simple mechanics problem to get you going. My personal choice would be a cylinder rolling down an incline without slippling - it has a lovely simple answer that really leverages mathematics and demonstrates the clarifying power of well constructed equations.

 

If we continue with wild speculative ideas that cannot be modelled due to a lack of any clear foundation or meaning then I will be forced to lock this thread.

 

[Relative]

!

Moderator Note

 

Relative

 

If you want guidance in creating physical models and obtaining predictions from them then we MUST use a simple example. I would suggest a simple mechanics problem to get you going. My personal choice would be a cylinder rolling down an incline without slippling - it has a lovely simple answer that really leverages mathematics and demonstrates the clarifying power of well constructed equations.

 

If we continue with wild speculative ideas that cannot be modelled due to a lack of any clear foundation or meaning then I will be forced to lock this thread.

 

Thank you for the advice,please do not close the thread, it is in homework section, my home work is to learn science and eventually to create a model that is understood.

 

 

I am now confused, because in one posters advice he mentions , make a complete new model, or make some complete new maths, I thought that is what I was doing.

 

''Sometimes you need to create your own correlation, because no formula exists yet.

Then, if you are lucky, you know all the variables, and can calculate your answer now. ''

Ok I will start with a cylinder rolling down a hill,

You mean like this?

D been distance

 

X been incline

How longs the grass?

 

is there any bumps in the hill?

 

Is the hill dry or wet?

 

What material is the cylinder made of?

 

How high is the hill, because at altitude there would be less gravity making the ma slower?

Weather conditions?

how big of a circumference has my cylinder got?

And what would be the purpose of the model, what are we trying to show?

And my new model was meant to represent this

 

 

This

[swansont]

Thank you for the advice,please do not close the thread, it is in homework section, my home work is to learn science and eventually to create a model that is understood.

 

 

I am now confused, because in one posters advice he mentions , make a complete new model, or make some complete new maths, I thought that is what I was doing.

 

''Sometimes you need to create your own correlation, because no formula exists yet.

Then, if you are lucky, you know all the variables, and can calculate your answer now. ''

Ok I will start with a cylinder rolling down a hill,

f=.jpg

You mean like this?

D been distance

 

X been incline

How longs the grass?

 

is there any bumps in the hill?

 

Is the hill dry or wet?

 

What material is the cylinder made of?

 

How high is the hill, because at altitude there would be less gravity making the ma slower?

Weather conditions?

how big of a circumference has my cylinder got?

 

You have to incorporate the path, but also worry about whether there is friction and if the cylinder will rotate.

 

Then you apply physical principles to the problem: you can use forces, and you could/should also apply conservation of energy

 

What physical principle is represented by putting the earth and the sun on a picture of the EM spectrum and the sound spectrum?

[Relative]

 

You have to incorporate the path, but also worry about whether there is friction and if the cylinder will rotate.

 

Then you apply physical principles to the problem: you can use forces, and you could/should also apply conservation of energy

 

What physical principle is represented by putting the earth and the sun on a picture of the EM spectrum and the sound spectrum?

The Physical picture of the ''black walls of space, this represent that C over distance becomes so red shifted, that we simply can not see, and my model was trying to show that the visual volume of space is directly proportional to the Suns energy and size etc. A bit like putting a 40 w light bulb in the center of a football pitch with no other light.

That would be un-proportional.

 

And what do you mean by incorporate a path ? I though the path was down hill?

And what friction? I thought friction was associated with heat, would heat not be lost has quick has gained by the rotation?

arrr, i got yea now, i did account for friction when i asked if the surface had grass etc.

[swansont]

The Physical picture of the ''black walls of space, this represent that C over distance becomes so red shifted, that we simply can not see, and my model was trying to show that the visual volume of space is directly proportional to the Suns energy and size etc. A bit like putting a 40 w light bulb in the center of a football pitch with no other light.

That would be un-proportional.

You need to tie such ideas in with physical principles. Light gets dimmer as you move away from the source because of the inverse-square law. That's a mathematical model, made from looking at a unit area on a sphere with differing radii.

 

 

And what do you mean by incorporate a path ? I though the path was down hill?

 

And what friction? I thought friction was associated with heat, would heat not be lost has quick has gained by the rotation?

 

arrr, i got yea now, i did account for friction when i asked if the surface had grass etc.

The path includes things you've mentioned, like the incline, whether there are bumps, is it curved or straight, etc.

 

Friction is a force and is associated with a loss of energy, and will also tell you if the object rolls or not, which affects the answer. Whether you assume that heating can be neglected is another part of the model.

[Relative]

You need to tie such ideas in with physical principles. Light gets dimmer as you move away from the source because of the inverse-square law. That's a mathematical model, made from looking at a unit area on a sphere with differing radii.

 

 

 

The path includes things you've mentioned, like the incline, whether there are bumps, is it curved or straight, etc.

 

Friction is a force and is associated with a loss of energy, and will also tell you if the object rolls or not, which affects the answer. Whether you assume that heating can be neglected is another part of the model.

If the hill was ice, then there would be little friction and the cylinder would slide down the hill gaining momentum, I do not understand what is the importance of this, what is the findings we are looking for?

 

There would be too many variables to consider , meaning an inconclusive test.

''You need to tie such ideas in with physical principles. Light gets dimmer as you move away from the source because of the inverse-square law. That's a mathematical model, made from looking at a unit area on a sphere with differing radii.''

 

And I disagree with this , but that is another story involving isotropic.

[Fuzzwood]

No it isn't. You are overthinking things here.

[imatfaal]

If the hill was ice, then there would be little friction and the cylinder would slide down the hill gaining momentum, I do not understand what is the importance of this, what is the findings we are looking for?

 

There would be too many variables to consider , meaning an inconclusive test.

...

 

This is why we create models - there might well be too many variables in a real world situation for a really accurate prediction; but we can use modelling to create simplified scenarios which we can work on

 

''You need to tie such ideas in with physical principles. Light gets dimmer as you move away from the source because of the inverse-square law. That's a mathematical model, made from looking at a unit area on a sphere with differing radii.''

 

And I disagree with this , but that is another story involving isotropic.

 

This response encapsulates your problem with physics - you are given a well known piece of information and the mathematical model behind it and you state your disagreement with little sense and no physics.

[Relative]

No it isn't. You are overthinking things here.

No it isn't what sorry, what are you referring too? and no such thing as over thinking.

 

This is why we create models - there might well be too many variables in a real world situation for a really accurate prediction; but we can use modelling to create simplified scenarios which we can work on

 

 

This response encapsulates your problem with physics - you are given a well known piece of information and the mathematical model behind it and you state your disagreement with little sense and no physics.

I can not talk about anything but models, that is why I stated that is another story.

 

And If you want me to accept something, it needs to be accurate,

 

You have not even told me what senario we are looking for, what model am i trying to create for the cylinder, what findings am I looking for?

Time it takes to get down the hill?

 

Average velocity?

I can think of several things to calculate about a cylinder rolling down a hill, but they all would be pretty meaningless because of too many variables.

 

I do not understand what you are asking me to work out, what should the model predict?

Edited August 29, 2014 by Relative

[Ophiolite]

No it isn't what sorry, what are you referring too? and no such thing as over thinking.

I can not talk about anything but models, that is why I stated that is another story.

 

And If you want me to accept something, it needs to be accurate,

 

You have not even told me what senario we are looking for, what model am i trying to create for the cylinder, what findings am I looking for?

Time it takes to get down the hill?

 

Average velocity?

You are overthinking things. You need to minimise the number of variables to more readily understand their inter-relationship. Therefore you ignore all that incidental crap about the hill's vegation and variations in slope. This is a smooth plane, with a constant slope and a perfect, smooth cylinder, released in such a way that the centre line of the cylinder is parallel to the ground (or the strike of the slope. Time how long it takes to reach specific points on the slope. Build a model from those observations. Repeat with a different slope. With different materials for the cylinder. With different diameters of cylinder. Gradually add variables to the model.

[Relative]

And what are we trying to show?

 

and i know it should be LB for pound ....pfff

[imatfaal]

1. what forces act on the cylinder? no need for figures - just names, points of action, and directions