Converting Cartesian Coordinates to Cylindrical Coordinates

In summary, to express a line y = -5 in cylindrical coordinates, you would use the equation y = r sin(phi). To express a point (0,-5) in cylindrical coordinates, you would use the equations x = r cos(phi) and y = r sin(phi), and solve for r and phi in terms of x and y. In 3D, cylindrical coordinates include a z component, but for this problem, the z component can be ignored.
  • #1
seang
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Homework Statement



Say I have line, y = - 5 in cartesian coordinates. How do I express this in cylindrical coordinates?

Also, if I have a point (0,-5) in cartesian coordinates, how to I express this position vector in cylindrical coordinates?

Homework Equations



y = r sin (phi)

j = r(hat)cos (phi) - phi(hat) sin (phi)


The Attempt at a Solution



THe relations are right there but I've forgotten howto use them.
 
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  • #2
do you remember how to turn say [tex](x,y)[/tex] into [tex](r,\theta)[/tex] in 2D? the idea there is similar...
 
  • #3
Cylindrical coordinates? That's in 3d but you only mention 2 coordinates? Perhaps you mean polar coordinates- cylindrical coordinates but ignore the z component.

You mention [itex]y= r sin(\phi)[/itex] (I would have used [itex]\theta[/itex]). Do you also know that [itex]x= r cos(\phi)[/itex]? Solve those two equations for r and [itex]\phi[/itex] in terms of x and y. The first is easy! You can eliminate [itex]\phi[/itex] by squaring both equations and adding. The second is about as easy: eliminate r by dividing one equation by the other.
 

What are cylindrical coordinates?

Cylindrical coordinates are a type of coordinate system used in mathematics and physics to describe the position of a point in three-dimensional space. They consist of a radial distance, an angle, and a height or depth.

How are cylindrical coordinates represented?

In cylindrical coordinates, a point is represented by the ordered triple (r, θ, z), where r is the radial distance, θ is the angle measured from a reference direction in the xy-plane, and z is the height or depth measured along the z-axis.

What is the relationship between cylindrical and cartesian coordinates?

Cylindrical coordinates can be converted to cartesian coordinates using the following equations: x = rcos(θ), y = rsin(θ), z = z. Similarly, cartesian coordinates can be converted to cylindrical coordinates using the equations: r = √(x^2 + y^2), θ = tan^-1(y/x), z = z.

What are the advantages of using cylindrical coordinates?

One advantage of cylindrical coordinates is that they are particularly useful for describing objects with circular or cylindrical symmetry. They are also useful in solving certain types of partial differential equations, such as those involving cylindrical symmetry.

How are cylindrical coordinates used in real-world applications?

Cylindrical coordinates are used in a variety of fields, including engineering, physics, and astronomy. They can be used to describe the position of objects in space, the motion of particles in a fluid, or the shape of cylindrical objects such as pipes or lenses.

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