Hey Ray! Explaining the Archimedes Principle – CBS Pittsburgh

PITTSBURGH (KDKA) – Physics can seem strange at times, and our experiments today are no different. Let’s do the test first, then we’ll explain. This experiment is also an easy one. All you need is a scale, an orange, and a glass of water large enough for the orange to fit.

(Photo Credit: Ray Petelin)

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Weigh oranges. Here our orange is 3.8 ounces.

Now drop it into the water. You’ll notice it floats, as this 3.8 oz orange is less dense than water.

(Photo Credit: Ray Petelin)

Next, let’s peel the oranges and weigh them again.

(Photo Credit: Ray Petelin)

Now this orange is 2.9 ounces. Almost an ounce lighter than when it was in the shell.

Now, when we drop this orange in the water, will it float in higher water or sink?

When we drop this into the water, will it stay the same, float higher or sink?

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Although it is lighter, it sinks. An outcome that is probably different from what most people expect.

(Photo Credit: Ray Petelin)

To find out how this works, we have to look to Archimedes, an ancient Greek mathematician and inventor. He formulated the Archimedes Principle, a physical law of buoyancy. It indicates that any “body” that is fully or partially submerged in a liquid and at rest will be acted upon by an upward or buoyant force, equal in magnitude to the weight of the liquid that the body transferable.

I know that sounds confusing. Simply, whether an orange floats in a liquid or not, depends on a few things.

First, gravity pulls the orange down. Second, there is a buoyant force, or a force that pushes the orange back in that liquid. When the orange is placed in the liquid, the two forces act in opposite directions. Gravity pulls the orange down. Then the buoyant force pushing upwards equal to how many parts of the water caused the orange to move.

(Photo Credit: Ray Petelin)

With the peel, the orange can hold more water, increasing its buoyancy enough to float. There are also small air pockets in the orange peel that help reduce its density.

(Photo Credit: Ray Petelin)

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When you peel an orange, it can’t move enough water to beat the gravity that is pulling the orange down, which means it will sink, even though it’s lighter.