Sketching polar curves a spiral

Sketching polar curves a spiral

Sketching Polar Curves - A Spiral

Definition

  • Polar curves are curves that are defined using polar coordinates rather than Cartesian coordinates.
  • A spiral polar curve or r = θ, often referred to as an Archimedean spiral, moves farther away from the origin as θ increases.

Sketching Polar Curves

Steps to draw a spiral polar curve:

  • Identify the initial and terminal points on your polar graph by looking at the limits given for θ.
  • Mark these points on your graph, along with key points between these limits, such as when θ=90° (π/2 radians) or 180° (π radians).
  • Plot the points by converting θ to degrees or radians, and then determining the corresponding r value using the given polar equation.
  • Draw the curve smoothly through these points, making sure the curve always spirals away from the origin.

Polar to Cartesian Form

  • The spiral polar curve r = θ can be converted to Cartesian coordinates using the formulas x = r cos θ and y = r sin θ.
  • Convert r to θ using the polar equation of the spiral curve, resulting in x = θ cos θ and y = θ sin θ.

Key Properties of Spiral Polar Curve

  • A spiral polar curve rotates about the origin, receding from the origin as it does so.
  • It creates an infinite number of “loops”, each further from the origin than the last.
  • Polar curves do not only represent curves in the plane; they can also represent a family of surfaces in space through rotation about a coordinate axis.

Examples

  • Given the spiral polar curve r = θ, we can sketch it by plotting these set points for θ = 0°, 90°, 180°, and 270° and connecting them in a smooth spiral away from the origin.
  • The corresponding r values for these points on the curve will be 0, π/2, π, and 3π/2 respectively.

Key Points

  • Sketching a spiral polar curve involves understanding polar coordinates and knowing how to convert between polar and Cartesian coordinates.
  • The key to sketching is to plot key points and ensure that the drawn spiral continually moves away from the origin.
  • Understanding the properties of the curve is also crucial for effective sketching in the Core Pure section of further mathematics.