dot product and cross product of vectors in physics pdf

Dot Product And Cross Product Of Vectors In Physics Pdf

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Vector Analysis Physics Pdf

I follow your graphical derivation in Figure 1b which, by the way, will look quite different when Bx is negative , but I still want to connect it to an intuition behind the remarkably simple formula. I haven't got an answer, but here are two thoughts in this direction Avi asked "Why should the area be related to..

It should give answers on polygons there may exist 'un-measurable' sets, but polygons in particular should be OK , and in particular on parallelograms. So, call by C u,v the area Content of the parallelogram defined by two vectors u and v. Combining these, C is bilinear -- linear in each of u and v separately -- like the cross-product. You have to allow orienation-dependent signs for C, for this to work.

This corresponds to choice of unit square mm? So the area is given by Ax By - Ay Bx , and this is the only formula it could possibly have. Notice that all of this does not need right-angle-dependent ideas like rotation. Very nice article Eli.

The arbitrary and unmotivated way the cross product was introduced at least to me eons ago in school always bugged me. Since then I'd seen formulations of the cross product that made much more sense to me ie: as the dual of a bivector in Clifford Algebra, where one also has an area interpretation , but it was nice to step back and see the sort of simple explaination that I would have wanted to see had I still been in high school the first time I'd seen this.

Finally a simple way to illlustrate the dot and cross product. No more "multiplication of vectors" which they aren't, by the way. Maybe if more people used your methods, people would stop thinking physics is a bunch of random, esoteric, memorization problems.

It is taking forever for your page to load. Perhaps not generating images dynamically and exporting the images as static PNGs would speed up your site, as it is pretty difficult to understand the explanation without appropriate images.

Anonymous - Thanks for your comment. It seems that CodeCogs who the equation images go through is having some difficulties.

I'm going to see if I can come up with a better way to do this. However, you can always download the PDF version which has all the equations. Anonymous, Put most simply: You use a dot product if you need to find bits of vectors that are parallel, you use a cross product if you need to find bits of vectors that are perpendicular. Does that help? Hello eli, What does it mean by bits of vectors? Sort of like a component to it? Could you give me some example of any physical meaning to dot and cross product?

Do you want a physical application? Anonymous, Sorry for the delay. A physical application of the dot product arises when calculating work. The work is the integral of the force which acts along the direction of motion times the displacement, i.

The torque is the force acting perpendicular to an arm times the length of the arm, or r x F Does this help? Can you explain this?

How can I add a diagram? Thanks dude! Is always good to see that there are people who value discussions and real math over just methods and calculations with no context. I Studied today your paper and your idea is awesome! But I have a problem with 9. I calculated it and i didn't get the area of the parallelogram Can you please explain me this equation?

Thanks for your comment. I am not entirely sure I understand your question, though. The magnitude of the cross product of A and B should be the unsigned area of the parallelogram. Can you give me a specific example where this does not work? I discuss this just after equation 3. In short, because the area has some directionality to it there's a normal to a plane which depends on which plane the area is in, we need a vector quantity for the area result.

Wow, I was trying to find the definition of the cross product using the dot product, something like: A. This geometric proof is so simple and elegant. Thank you for making this post. Solutions from the brain, not the butt. Pages Home About this blog. The dot product and cross product of two vectors are tools which are heavily used in physics. As such, they are typically introduced at the beginning of first semester physics courses, just after vector addition, subtraction, etc.

Although they are not strictly required for these intro courses see [1], for example , they make the development and computations of work and energy, torque, and electromagnetism far simpler. Unfortunately, they are consistently introduced in an awful way: by straight definition. That is, using the dot product for example, for two vectors and they say something like. We define the dot product between and as:.

Although a few of these give a geometric interpretation after the fact, it is usually in passing, and does not really contribute to their discussion. These approaches are not limited to textbooks, either. See [7] for an in-class lecture example. In these examples, the dot product is introduced first and then the cross product.

From one standpoint this makes some sense -- the dot product is definitionally simpler and usually easier to calculate. However, from a conceptual standpoint, I think this order is backwards. Furthermore, in my experience, students, by and large, miss the physical and graphical significance of these definitions, and upon encountering the concepts of work or torque later on, take the resulting expressions purely as definitions as well.

Personally, it is my inclination to wait to introduce these products until they're needed, thus motivating the discussion in the first place. In any case, my discussion follows the latter approach for better insertion into standard texts and presupposes understanding of vector basics: addition, decomposition, etc..

The Cross Product. Say we have two vectors and with lengths and , and we want to find something which is a measure of how much of is perpendicular to. Looking at Fig. The area of a parallelogram is. Thus area is a good measure of perpendicularity. There are two different ways of calculating this area. If the angle between the two vectors is , as in Fig. Alternatively, choosing as the base, we write the perpendicular part as.

Then the area is. However, if we don't know angle between them, we're not completely out of luck. If you look at Fig. Of course, I could just have easily labeled the axes and which would give a different area. If all we've done is relabel our axes, keeping and fixed, then we wouldn't expect the size of these areas to be different -- and they're not.

However, although the amount of area is the same, in a way the areas are different in that they're facing different directions in each case. So, we need a way to distinguish these three areas from each other, and from an arbitrarily oriented area. What we'll do is pick a vector perpendicular to both to -- and thus perpendicular to the area of the parallelogram -- with magnitude equal to the area.

We'll call this vector. However, in principle, we have a choice of two such perpendicular vectors. In Fig. Additionally, this arbitrariness can be seen in choosing whether to measure the angle in 3 from to or vise-versa. So, as a matter of convention, we'll decide to always measure angles from the first term in the cross product in 5 such that. Thus, the cross product represents how much these two vectors point in perpendicular directions , and is a signed area vector perpendicular to the plane described by and.

All we need to do is find out how much area is pointing in each direction. To do that, look at Fig. This picture shows what the area between the two vectors looks like if we look only at two coplanar components at a time -- in other words the , and components of the area. But we already know what each of these areas are from 8! So, then we can combine these equations and write the cross product.

Having discussed the perpendicularity of two vectors, it's natural to ask if there's a similar measure of the parallelity of two vectors. There are two ways of doing this. The way I'll do it first is explicitly geometrical, the second way is only implicitly geometrical. Say we have two vectors and again, and we want to know how much of is pointing projected along.

From Fig. Similarly, the amount of that is projected along is.

Difference between Dot Product and Cross Product in tabular form

It has many applications in mathematics, physics , engineering , and computer programming. It should not be confused with the dot product projection product. If two vectors have the same direction or have the exact opposite direction from one another i. The cross product is anticommutative i. Like the dot product , it depends on the metric of Euclidean space , but unlike the dot product, it also depends on a choice of orientation or " handedness ".

Vector dot product and cross product are two types of vector product, the basic difference between dot product and the scalar product is that in dot product, the product of two vectors is equal to scalar quantity while in the scalar product, the product of two vectors is equal to vector quantity. Your email address will not be published. Save my name, email, and website in this browser for the next time I comment. Related Articles. Second Equation of Motion October 7, Difference between elastic and inelastic collision with examples July 8,

Physics Stack Exchange is a question and answer site for active researchers, academics and students of physics. It only takes a minute to sign up. Connect and share knowledge within a single location that is structured and easy to search. To me, both these formulae seem to be arbitrarily defined although, I know that it definitely wouldn't be the case. If the cross product could be defined arbitrarily, why can't we define division of vectors?

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Physics Stack Exchange is a question and answer site for active researchers, academics and students of physics. It only takes a minute to sign up. As cross product is vector. Anyone can define this Please? The simplest answer is: they are defined that way, so that's the way it is.

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I follow your graphical derivation in Figure 1b which, by the way, will look quite different when Bx is negative , but I still want to connect it to an intuition behind the remarkably simple formula. I haven't got an answer, but here are two thoughts in this direction Avi asked "Why should the area be related to.. It should give answers on polygons there may exist 'un-measurable' sets, but polygons in particular should be OK , and in particular on parallelograms. So, call by C u,v the area Content of the parallelogram defined by two vectors u and v.

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 Вот тут-то вы и рассмотрели его кольцо.

1 comments

Capucine F.

Furthermore, the dot symbol “⋅” always refers to a dot product of two vectors, not traditional multiplication of two scalars as we have previously known. To avoid.

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