Paper blade

Can pa­per cut met­al or co­conut? It can if it ro­tates fast enough!

Safe­ty pre­cau­tions

• Dan­ger! Only un­der adult su­per­vi­sion!
• Be sure to wear gloves, eye­wear, and a face mask dur­ing the ex­per­i­ment!

Equip­ment

• an­gle grinder;
• pa­per;
• pen­cil;
• alu­minum can;
• co­conut;
• gloves;
• gog­gles;
• and a mask.

Step-by-step in­struc­tions

Cut out sev­er­al iden­ti­cal pa­per cir­cles. Glue them to­geth­er to make two- and three-lay­er blades. At­tach the cir­cles to a saw. Put on gloves, pro­tec­tive eye­wear, and a mask. Let's see if “pa­per can beat scis­sors!”

Process de­scrip­tion

The in­cred­i­ble cut­ting prop­er­ties of or­di­nary pa­per can be ex­plained by the con­cept of “cen­trifu­gal force.” Cen­trifu­gal force is a fic­ti­tious force of in­er­tia that aris­es from the ro­ta­tion of the pa­per disks. This force is di­rect­ed ra­di­al­ly out­ward from the axis of ro­ta­tion. In or­der to bend, the one needs to over­come the in­flu­ence of cen­trifu­gal force. But how does this lead to pa­per cut­ting met­al?

First, let’s talk about why sharp ob­jects cut. It's all about the pres­sure. Blades are very thin, and there­fore, the force ap­plied to them cre­ates strong pres­sure on the sur­face that needs to be cut. In oth­er words, blades cut sim­ply by push­ing through the ob­jects in their path. But pres­sure alone is not enough: this process also re­quires trans­la­tion­al mo­tion, as fric­tion in­creas­es cut­ting ef­fi­cien­cy. This is why we don’t just press down­wards, but ac­tive­ly “saw” with a blade when mak­ing a cut.

As you know, fric­tion caus­es ob­jects to heat up – so why doesn’t the pa­per in our makeshift blade ig­nite from the fric­tion? First­ly, the heat is dis­trib­uted over the en­tire edge of the disk, and sec­ond­ly, dur­ing its ro­ta­tion, the pa­per man­ages to cool in the sur­round­ing air.