Density facts for kids
Density is a way to measure how much "stuff" is packed into a certain space. Imagine you have a box. If you fill that box with feathers, it won't weigh much. But if you fill the same box with rocks, it will be very heavy! The box full of rocks has a higher density than the box full of feathers.
So, density tells us how much mass (the amount of matter) an object has compared to its volume (the amount of space it takes up). If an object has a lot of mass in a small space, it has high density. If it has little mass in a large space, it has low density.
You can find density by dividing an object's mass by its volume.
- Density = Mass ÷ Volume
Contents
How Density Changes
Density can change if you change the pressure or the temperature of a material.
Pressure and Density
If you increase the pressure on something, you push its particles closer together. This makes the object more dense. Think about squeezing a sponge – it gets smaller and more packed.
Temperature and Density
Usually, when you make something hotter, its density goes down. This is because the particles spread out more when they get warmer. For example, hot air is less dense than cold air, which is why hot air balloons float!
However, water is a bit special. When water gets colder, its density usually increases, but only until it reaches 4 °C. Below 4 °C, as water gets even colder, it actually starts to expand a little. When water freezes into ice at 0 °C, it expands by about 9%. This makes ice less dense than liquid water, which is why ice floats!
Measuring Density
Scientists use different ways to measure density.
Specific Gravity
Sometimes, people compare the density of a substance to the density of fresh water. This comparison is called specific gravity. If something has a specific gravity of 2, it means it's twice as dense as water.
Density Units
The most common units for density are grams per cubic centimeter (g/cm3) or kilograms per cubic meter (kg/m3).
- If a substance has a high density, it means there are many grams of matter packed into each cubic centimeter.
- If a substance has a low density, it means there are fewer grams of matter in each cubic centimeter.
Other Kinds of "Density"
The word "density" isn't just used for mass and volume. It can also describe how much of something is found in a certain area or space.
Population Density
Population density tells us how many people live in a specific area. For example, cities usually have a much higher population density than the countryside because many people live close together in a smaller space.
Storage Density
In computers, storage density means how much data can fit onto a data storage device compared to its physical size. A Blu-ray disc can hold much more data than a DVD, even though they are about the same size. This means a Blu-ray disc has a higher storage density.
Images for kids
-
This chart shows the molar volumes of elements in their liquid and solid forms.
See also
In Spanish: Densidad para niños
