Question

Discuss Lissajou figures in general ?

Answer 1

We can obtain very interesting graphs when each of the x- and y- coordinates are given as functions of t. In this case, we have parametric equations. (We see another example of parametric equations later in the applications of differentiation section.)

Lissajous Figures are a special case of parametric equations, where x and y are in the following form:

x=A sin(at+?)

y=B sin(bt+?)

[These can also be written in terms of cosine expressions, or a combination of sin and cos, since we can shift sine onto cosine easily. See Graphs of y = a sin(bx + c).]

Lissajous curves can be seen on oscilloscopes and are the result of combining 2 trigonometric curves at right angles.

Example 1

Sketch the graph of the parametric equation where:

x = 2 cos t
y = cos(t + 4)

Common Lissajous Curves

Lissajous curves take certain common shapes depending on the values of the variables in the expressions

x = A sin(at + ?) and
y = B sin(bt + ?)

In Example 1, we saw that the curve was an ellipse. If A ? B and a = b, we obtain an ellipse. (See more on the Ellipse.)

In the example in Curvilinear Motion, the Lissajous figure is a circle. If A = B and a = b = 1, we will get a circle.