P is a point on the circumference of a circle radius r which rolls,
without slipping, inside a circle of radius 2r. What is the locus
The coke machine in college takes 50 pence pieces. It also takes a certain foreign coin of traditional design...
What happens to the perimeter of triangle ABC as the two smaller
circles change size and roll around inside the bigger circle?
As an extension to this problem, can you now work out how much
of the circumference of the disc never touches the edge of the
The article 'A
Rolling Disc' discusses variations of this problem.