Alice and Bob are two high school students who are curious about density. They decide to do some experiments with different materials and liquids to learn more about this property.
They start by measuring the mass and volume of some solid objects, such as a metal cube, a wooden block, and a plastic ball. They use a balance to measure the mass in grams, and a ruler to measure the length, width, and height in centimeters. They calculate the volume by multiplying the three dimensions, and then divide the mass by the volume to get the density in grams per cubic centimeter (g/cm3).
They record their results in a table:
| Object | Mass (g) | Volume (cm3) | Density (g/cm3) |
|--------|----------|--------------|-----------------|
| Metal cube | 200 | 8 | 25 |
| Wooden block | 60 | 24 | 2.5 |
| Plastic ball | 40 | 32 | 1.25 |
They notice that the metal cube has the highest density, followed by the wooden block, and then the plastic ball. They wonder what would happen if they put these objects in water. They fill a large container with water and mark the water level. Then they carefully lower each object into the water and observe what happens.
They see that the metal cube sinks to the bottom of the container, the wooden block floats on the surface, and the plastic ball sinks halfway. They also notice that the water level rises when they add each object. They measure the new water level and subtract the original water level to get the volume of water displaced by each object. They record their results in another table:
| Object | Volume of water displaced (cm3) |
|--------|--------------------------------|
| Metal cube | 8 |
| Wooden block | 24 |
| Plastic ball | 32 |
They compare the two tables and realize that the volume of water displaced by each object is equal to the volume of the object itself. They also notice that the density of the object determines whether it sinks or floats in water. They recall that the density of water is about 1 g/cm3, so any object with a density higher than that will sink, and any object with a density lower than that will float. They also learn that the object's weight does not affect its buoyancy, only its volume and density.
They decide to try another experiment with different liquids, such as oil, alcohol, and honey. They pour each liquid into a separate container and measure their mass and volume. They calculate their density using the same formula as before. They record their results in a third table:
| Liquid | Mass (g) | Volume (cm3) | Density (g/cm3) |
|--------|----------|--------------|-----------------|
| Oil | 80 | 100 | 0.8 |
| Alcohol | 80 | 100 | 0.8 |
| Honey | 140 | 100 | 1.4 |
They notice that the oil and alcohol have the same density, but lower than water, while the honey has a higher density than water. They wonder what would happen if they mixed these liquids with water. They take four identical glasses and fill them halfway with water. Then they add a different liquid to each glass and observe what happens.
They see that the oil floats on top of the water, forming a separate layer. The alcohol mixes with the water, forming a homogeneous solution. The honey sinks to the bottom of the water, forming another layer. They also see that the water level rises when they add each liquid. They measure the new water level and subtract the original water level to get the volume of liquid added to each glass. They record their results in a fourth table:
| Liquid | Volume of liquid added (cm3) |
|--------|-----------------------------|
| Oil | 50 |
| Alcohol | 50 |
| Honey | 50 |
They compare the four tables and realize that the volume of liquid added to each glass is equal to the volume of the liquid itself. They also notice that the density of the liquid determines whether it floats or
Eva and Max are two high school students who are curious about density. They decide to do some experiments with different objects and liquids to learn more about this concept.
They start by collecting some objects that have different shapes, sizes, and materials, such as a marble, a ping pong ball, a rubber duck, a metal spoon, and a wooden stick. They use a scale to measure the mass of each object in grams, and a measuring cup to measure the volume of each object in milliliters. They calculate the density of each object by dividing the mass by the volume, and record their results in a table:
| Object | Mass (g) | Volume (mL) | Density (g/mL) |
|--------|----------|-------------|----------------|
| Marble | 20 | 5 | 4 |
| Ping pong ball | 2 | 30 | 0.07 |
| Rubber duck | 50 | 100 | 0.5 |
| Metal spoon | 30 | 10 | 3 |
| Wooden stick | 10 | 20 | 0.5 |
They notice that the density of each object depends on how much mass it has in a given volume, and that different materials have different densities. They wonder what would happen if they put these objects in different liquids, such as water, oil, and honey. They fill three large jars with equal amounts of each liquid, and label them accordingly. They carefully drop each object into each jar and observe what happens.
They see that some objects sink to the bottom of the jar, some objects float on the surface of the liquid, and some objects stay in the middle of the liquid. They also see that the liquids form layers in the jar, with honey at the bottom, water in the middle, and oil at the top. They measure the density of each liquid using a hydrometer, which is a device that floats in the liquid and shows the density on a scale. They record their results in another table:
| Liquid | Density (g/mL) |
|--------|----------------|
| Water | 1 |
| Oil | 0.8 |
| Honey | 1.4 |
They compare the two tables and realize that the density of the object determines whether it sinks or floats in the liquid, or stays in the middle. They learn that an object will sink in a liquid if its density is higher than the liquid's density, and it will float in a liquid if its density is lower than the liquid's density. They also learn that an object will stay in the middle of a liquid if its density is equal or close to the liquid's density. They also learn that the density of the liquid determines the order of the layers in the jar, with the highest density at the bottom and the lowest density at the top.
Eva and Max are satisfied with their experiments and feel that they have learned a lot about density. They decide to write some questions and answers based on their observations to test their knowledge. Here are some examples:
Q: What is the formula for calculating density?
A: Density = mass / volume
Q: What is the unit for density?
A: Grams per milliliter (g/mL)
Q: What is the density of water?
A: 1 g/mL
Q: What happens when an object with a higher density than a liquid is placed in the liquid?
A: It sinks.
Q: What happens when an object with a lower density than a liquid is placed in the liquid?
A: It floats.
Q: What happens when an object with a similar density to a liquid is placed in the liquid?
A: It stays in the middle.
Q: What happens when a liquid with a higher density than another liquid is added to the other liquid?
A: It sinks to the bottom, forming a layer.
Q: What happens when a liquid with a lower density than another liquid is added to the other liquid?
A: It floats on top, forming a layer.