A Geometric Coin Trick

Mathematicians called topologists study the shapes of various objects to characterize and understand them. Dr. Lisa Piccirillo is a topologist who sometimes studies shapes called knots. Shapes that topologists study can exist in different numbers of dimensions: for example, a circle on a piece of paper lives in two dimensional space, but a loop of thread lives in three dimensional space.

Try this activity from Science World to learn more about how shapes behave in different numbers of dimensions. You can also find a video demonstration of this activity from the Institute of Physics.

Illustration showing the coin trick. Top left has a piece of paper with a penny falling through the hole. Top right shows the penny having gone through the hole. Bottom left shows folding the paper. Bottom right shows that a nickel can't fall through the same hold as the penny without folding the paper.
A visual representation of the geometric coin trick.