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Question Video: Determining the Density of an Object Relative to the Densities of Oil and Water Science

The densities of water and a certain oil are given in the image below. An object is found to sink in the oil but float on water. What can be assumed about the density of the object?

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Video Transcript

The densities of water and a certain oil are given in the image below. An object is found to sink in the oil but float on water. What can be assumed about the density of the object? (A) Its density is greater than 0.9 grams per centimeter cubed but less than 1.0 grams per centimeter cubed. (B) Its density is less than 0.9 grams per centimeter cubed but greater than 1.0 grams per centimeter cubed. (C) Its density is greater than 0.9 grams per centimeter cubed and greater than 1.0 grams per centimeter cubed. (D) Its density is less than 0.9 grams per centimeter cubed and less than 1.0 grams per centimeter cubed. (E) Its density is exactly 0.95 grams per centimeter cubed.

Density is a value which we give to a substance or object when we measure its mass and divide this mass by the substance’s volume. We usually measure mass in grams, symbol lowercase g, and volume in centimeters cubed, unit symbol cm to the power of three.

We can measure the mass of a substance on a scale or balance. This diagram shows an electronic scale. And we can use various methods to measure the volume of a substance or object in centimeters cubed.

Another way to define density is to say it is the mass per unit volume of a substance. We can see this definition tells us the same thing as the formula. This is the mass. The divide line means in or per. And this is the volume. So we have mass per unit volume. Density is usually measured in grams per centimeter cubed.

Another way to think about density is how compact the particles in the substance or object are or how much mass is squeezed into a certain volume. We know that if we had a balloon the same volume as a rock, that the rock would be much heavier. The rock would have a greater mass. This is because the rock particles are packed very closely together. And there are many more particles in the rock than there are air particles in the balloon. Rock is much more dense than air. Rock has a high density compared to the air in a balloon.

Now, let’s look at the question. We are given two containers. One container holds oil. Oil has a density of 0.9 grams per centimeter cubed. The other container holds water. Water has a density of 1.0 grams per centimeter cubed. We are told that when an object is put into oil, the object sinks. And when it is put into water, it floats. We are asked what we can assume about the density of the object.

Let’s look at the first picture. The object sinks in the oil because its particles are more tightly packed and it has a larger density than the oil. In the second picture, we see that the object floats on water. This is because the object’s particles are less tightly packed than water’s particles. The object is less dense than water, and so it floats. Water has a larger density than the object. We can see that the object has a density between the density of oil and water.

Since oil has a density of 0.9 grams per centimeter cubed and since water has a density of 1.0 grams per centimeter cubed, we can assume that the density of the object is between 0.9 and 1.0 grams per centimeter cubed. When we look at the answer options, we can see that this matches answer option (A). The object’s density is greater than 0.9 grams per centimeter cubed but less than 1.0 grams per centimeter cubed.

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