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Using a balance to compare the masses of objects of different masses. Related content and interactive resources on this topic can be accessed on ngscience.com.

Inflate a balloon by blowing air into it. Notice that the balloon gets bigger. The amount of space the balloon takes up – its volume – increases. The air in the balloon, the balloon and even you are matter. Matter is anything that has mass and volume. Mass is the amount of matter an object has. Mass is measured using a scale or balance and is commonly measured in kilograms, grams, ounces or pounds. Volume is how much space the matter takes up. The foam ball and the baseball are both made of matter. Volume is commonly measured in cubic units, milliliters or liters. Observe the foam ball and the baseball on the balance. Notice that the foam ball takes up more space than the baseball – it has a greater volume. However, the baseball has a greater density and greater mass.

Matter is made up of tiny particles, called atoms. They are the basic unit of all matter. Atoms are so small they can only be seen with special high-powered microscopes. Matter typically exists in three forms or states – solids, liquids or gases. The state matter is in depends on the arrangement of its atoms.

States of Matter
The objects around you, such as your desk, chair, books and pencils are solid matter. Solids are matter that have a fixed shape and volume. The particles that make up solid matter are tightly packed together. This gives solid matter its rigid shape. The shape and volume of a solid does not change when it is placed in different containers. If you take a solid and move it between different containers, its shape and volume does not change.

Water, fruit juice and cooking oil are examples of matter in a liquid state. Like solids, liquids have a fixed volume. This means the amount of space taken up by a liquid always stays the same. Like solids, liquids cannot be compressed. Compared to a solid, the particles that make up a liquid are less tightly packed together. They are free to slide past each other. This property allows liquids to flow and change shape. A liquid will spread out to take the shape of the container it is in. When you pour some milk from a carton or bottle into a glass, the shape of the milk changes, but the volume of the milk remains the same.

Gases are matter that can change in both shape and volume. You can’t always see gases, but they are all around you. The air you breathe is a gas. The water vapor released from a boiling kettle is also a gas. If you take a balloon filled with air and squeeze it gently, you will notice that the shape of the balloon changes. When you let the air out of a balloon, the gas particles spread out in all directions. The gas takes the shape and fills the space of the container it is in. The particles that make up a gas are able to move about freely. This property allows gases to change in both shape and volume. Gases can be compressed. When a gas is compressed, its volume decreases. We compress air to fill a scuba tank. Inside the scuba tank, the compressed air takes up much less space than the air around you.

Take a sheet of scrap paper and fold it in half. By folding the paper, you have changed its shape. You have made a physical change to matter. A physical change is a change to matter in which no new matter is made. When a physical change is made to matter, the amount of matter does not change. If you take a block of chocolate and break it into pieces, the chocolate will have a different shape and appearance, but the amount of chocolate does not change. Physical change can also take place when matter is heated or cooled. If you heat the pieces of chocolate in a saucepan, they will melt into a liquid. If you turn off the heat and allow the chocolate to cool, it will form a solid again. When the chocolate changed from a solid to a liquid and back to a solid again, the amount of matter remained unchanged. Many physical changes, including those that involve a change in state, are reversible. This means the matter can be changed back to its state or condition before the physical change occurred.

Most matter changes state when it is heated or cooled. Some matter requires large increases or decreases in temperature before it changes state. Gold is a solid at room temperature. It needs to be heated to over 1,000oC (1,832oF) before it begins to melt. Other matter can change state more easily. On Earth, water exists in three states – as solid ice, liquid water and as the gas water vapor. Let’s take a look at the temperature changes that must take place for water to change from one state to another. At room temperature, water is in a liquid state. When water is cooled to 0oC (32oF), it begins to change into solid ice. This process is called freezing and the temperature at which this occurs is called its freezing point. So, the freezing point of water is 0oC.

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