WHICH WOULD FLOAT ON WATER? A PEELED ORANGE, OR AN UNPEELED ORANGE?

A. Materials needed:

1. A glass of water
2. One unpeeled orange

B. Instructions:

1. Half-fill a glass with clean water
2. Place the unpeeled orange into the water. Does it sink or float?
3. Peel the orange and repeat step 2. Does the peeled orange sink or float?
4. Wash your hands with soap under running water…and oh, it’s safe to enjoy your orange:)  Share your results with us!

SO WHY DOES THE UNPEELED ORANGE FLOAT EVEN THOUGH IT IS HEAVIER?

Do you remember Archimedes’ principle? When you immerse an object in a fluid (such as water) it will displace (or spill) some amount of water. We also know that water has some kind of an upwards force; for instance, if you hold an inflated balloon under water and release it suddenly, the balloon is propelled (pushed upwards), this push is deliberately done by the water:) It is called an upwards force, or upthrust!

So Archimedes says when an object is immersed in water, it will experience an upthrust which will be equal to the weight of water it displaces.

Therefore, the more water an object displaces, the more the upwards force it experiences. The peels of an orange consist of several pores, these air-filled pores increase its surface area and enable it to displace a greater amount of water. This also means that it experiences a greater upwards push from the water in which it is immersed. Because the upwards push by the water is huge enough, it overcomes gravitational force and the orange just can’t go any further into the water, thus floats.

TAKING IT FURTHER

Repeat this experiment with concentrated salt water (brine) and share your results with us.