Does an orange float or sink?

Safe­ty pre­cau­tions

None.

Equip­ment

• glass con­tain­er;
• wa­ter;
• two or­anges.

Step-by-step in­struc­tions

Toss the un­peeled or­ange in some wa­ter. Note that it floats. Put the peeled or­ange in the wa­ter – it sinks!

Process de­scrip­tion

Or­ange peels are por­ous and filled with air pock­ets. One can com­pare the peel to a life jack­et; it makes the or­ange’s av­er­age den­si­ty less than that of wa­ter, which al­lows the or­ange to float on the wa­ter's sur­face. But re­mov­ing the peel from the or­ange will cause it to sink im­me­di­ate­ly since the den­si­ty of the or­ange with­out its air-rid­dled peel is greater than the den­si­ty of the wa­ter.

The force push­ing the or­anges to the sur­face of the wa­ter is known as buoy­ant force, and can be cal­cu­lat­ed us­ing Archimedes’ prin­ci­ple. If the buoy­ant force on a cer­tain ob­ject ex­ceeds the force of grav­i­ty, the ob­ject with float on the sur­face of the wa­ter. Buoy­ant force is pro­por­tion­al to the vol­ume of the ob­ject, and thus the ob­ject’s av­er­age den­si­ty can in­di­cate whether or not the ob­ject will float. If the ob­ject’s av­er­age den­si­ty is greater than that of the wa­ter its vol­ume will dis­place, it will sink.