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Glossary of scientific terms.

Here you will find scientific terms that are used in our books as well as definitions of other science words that you may find helpful. We have tried to make the definitions simple enough for elementary school students to understand so if a science word you are looking for is missing or confusing as defined here, please let us know, and we will try to add it or clarify it for you.


Aristotle - Ancient Greek philosopher who was interested in how things worked.  He tried to explain how things worked without actually doing any experiments.  This made him get some things wrong, for example, how gravity works.  You can learn more about him by clicking here.

Astronauts - Astronauts are people who travel to outer space.  Sometimes they are also known as cosmonauts (Russian terminology) or taikonauts (Chinese terminology).

Atmosphere - is the layer of gases that usually surrounds a planet.  For Earth, we call this mixture of gases air.


Barometer - a device that is used to measure atmospheric pressure. Learn how to make your own barometer by clicking here.


Conserve - when something is conserved it does not change in value. For example, when you pour juice from a bottle into different glasses for your friends. Even if the shape and size of the different glasses change, the total volume of the juice would be the same as it was in the bottle. The total volume of the juice is conserved.


Density - the amount of something in a given measurement. For example, if you can fit two basketballs in one box, then the density of basketball for each box is 2. Another example, if you type 300 words on two pages, then the density of words per page is 150.


Experiment - A set of steps designed to test a hypothesis.  This usually includes makings observations and/or taking measurements of the interaction of objects.  For example, you might time how long it takes for different objects to fall to the ground from a certain height to see if it takes as long as you thought it would.


Force - A force is a pull or a push. For example, when you ride a bicycle, you have to push on the pedals to make the wheels turn.  You are using force to make the bicycle move.  Similarly, when you pull a cart you are using force.

Friction - A type of force that opposes movement.  For example, if you try to push a table to the left side of a room, the force of friction would be between the table's legs and the floor towards the right side of the room.


Galileo - You can learn more about Galileo by clicking here.

Gravity - is the force created by mass that attracts other objects to that mass.  For example, the Earth's gravity attracts us to it therefore keeping us firmly on the ground.  Check out the book, "Why Can't I Jump Very High? - A Book About Gravity" for more information.


Hypothesis - An educated guess or prediction about what might happen under certain circumstances.  For example, if you were to drop a feather and a hammer from the same height at the same time, your hypothesis might be that the hammer will hit the ground first, or it could be that they both fall together.


Isaac Newton - is one of the most famous physicist and mathematician that ever lived.  He came up with Newton's Three Laws of Motion and discovered the law of gravity.  He also invented a useful advanced way of doing mathematics, called calculus.  You can find out more about Sir Isaac Newton by clicking here.


Joule - is a measurement of energy. When you apply one newton of force over a distance of one meter, your body spends one joule of energy to do it.


kilogram - is a unit of mass.



Mass - The amount of stuff something is made of.  The more stuff something is made of, the more mass it has.  Suppose everything in the world were made up of marbles.  In this case you would be made out of more marbles than a piece of paper because you have more mass than a piece of paper.

Massive - Something with a lot of mass.


newton - is the unit of force. If you accelerate one kilogram of mass at one meter per second-squared, you are applying a force of one newton on it.


Orbit - An elliptical path that satellites and planets take around a more massive object.  For example, the planets in our solar system are in orbit around the sun, and the moon is a satellite in orbit around Earth.


Pressure - is the force applied over a certain area. If the force applied is much more than the area over which it is applied, the pressure is huge. If the area, however is much more than the force being applied the pressure is small.



Rate - change of one thing compared to another. For example, when you run, the distance you run in a certain amount of time is your speed. Another way to say it would be that your speed is the rate which you run.


Star - is a giant ball of gas in space that creates its own light through a process called nuclear fusion. The sun is our closest star.

Sublimation - is the process in which a solid object turns directly into a gas without becoming a liquid first. Dry ice, which is just solid carbon dioxide, goes through this process in




Vacuum - space that is completely empty of everything, including air.

Value - in science value usually is a number that tells you how big or small something is. For example, a dog usually has a mass that has a higher value than a kitten.

Variables - Variables are things that change in an experiment.  For example, when you plant sunflower seeds in different types of dirt to see which dirt is best for growing sunflowers, the variable is the different types of dirt you used.

Volume - tells you how much space something takes up.



X-ray - really high energy light that cannot be seen with human eyes. It is strong enough to pass through many different materials including the human body. This makes it useful for doctors to be able look inside you to see if everything is ok with you. For example, if you have a nasty fall while riding your bike, an x-ray photo of you can show if you have any broken bones.




Children reading science books.
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