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A radius is a straight line from the center of a circle to its outer edge. It is also used to describe the distance from a center point in any direction to mark an area.

The circumference is the distance around the outside edge of a circle or a round object. It is a measurement that tells you how long the boundary of a round shape is.

A perpendicular is a line that meets or crosses another line at a 90-degree angle. It is used in science and math to describe two lines that are perfectly square to each other.

A catalyst is something that makes a change happen faster or more easily. In science, it is a substance that speeds up a chemical reaction without being changed itself.

A solute is a substance that is dissolved in another substance, usually a liquid. It is the part of a mixture that disappears into the liquid to create a solution.

Heredity is the process by which physical or mental qualities are passed from parents to their children through genes. It explains why family members often share similar traits like eye color, height, or certain health conditions.

Symbiosis is a close relationship between two different living things that live together. Usually, this relationship helps at least one of them, and often both organisms benefit from each other.

Energy is the power that comes from things like electricity, coal, or the sun to make machines work or provide heat. It also describes the physical and mental strength that people have to be active and do things.

Gravity is the natural force that pulls objects toward each other, especially toward the center of the Earth. It is what makes things fall to the ground and keeps us from floating away into space.

Friction is the force that happens when two surfaces rub against each other. It makes it harder for things to move and can create heat.