Question: What makes an orange float or sink in water?

KIDS’ LAB LESSONS

Experiment Overview

When first exploring water, many children wear water wings, life jackets, or other aids to help them stay afloat. But what does a piece of fruit wear in the water if it wants to keep from sinking? In this experiment, you will place fruits in water with and without their peels and decide which peels help keep their fruits high and dry.

Science Concept

The Greek scientist Archimedes once famously shouted “Eureka—I've found it!” when he discovered the concept of buoyancy and ran through the streets of town announcing his discovery. Unfortunately, this realization came to him while he was bathing in his bathtub … wearing no clothes. What Archimedes figured out is that objects have to move water out of the way in order to be placed in it. That water has weight. He found that the weight of that displaced water is the same as the force that lifts up the object in the water. If that force is enough, the object can float. A block of wood is an example of something that experiences a buoyant force equal to its weight. A bowling ball, however, doesn't experience a large enough buoyant force, and so it sinks.

Materials

• Several pieces of fruit

• Large bowl of water

• Adult helper

• Knife, for peeling the fruit

Procedure

1. Select a fruit and predict whether or not it will float when placed in the water.

2. Place the fruit in the water and observe whether or not it floats.

3. Ask your adult helper to assist you as you peel the fruit.

4. Once you have completely removed the peel, place the fruit in the water again and observe whether or not it floats.

5. Select another fruit and repeat steps 2–4. Do this for each fruit that you have selected for the experiment.

Questions for the Scientist

1. Which fruits floated when they still had their peels?

2. For the fruits that floated with their peels, what about their peels made them float?

3. Which fruits floated even without their peels?

4. Was there something those floating fruits had in common that made them float, even without their peels?

5. Using what you observed in this experiment, describe an outfit you could wear that would help keep you afloat in a swimming pool.

Follow-Up

Oranges tend to produce very specific results in experiments such as this one. That is because of the way their peels are made. On the surface of orange peels are hundreds of tiny pits that collect air. Collectively, these air pockets act like a sort of life preserver for the orange, and keep it afloat. When the peel is removed, the inside of the orange is heavier than the water, and it sinks to the bottom of the bowl. Other fruits that do not have these pits in their peels tend not to float as well as the oranges do. As a follow-up experiment, try other liquids such as salt water (which tends to be more dense than fresh water) or fruit juice to see if the same fruits produce the same results in these other liquids.