Phases of Matter
We know water can freeze into solid ice, but what about the invisible air all around us? Can gases turn into liquids, or even solids, if they get cold enough?
Is it Possible to Freeze Air?
It turns into a liquid! At extreme cold, the rapidly moving gas molecules slow down and get closer together until they form liquid nitrogen.
Yes! If you cool it even further to around -210 degrees Celsius, those liquid molecules lock into place and form solid nitrogen ice.
Put Your Instincts to the Test
Think about what you already know about temperature and phases. Pick an answer for each question, then see if your instincts were right.
It shatters into pieces like glass. Liquid nitrogen is so cold that it removes a massive amount of energy from the rubber. The molecules slow down and pack tightly together, causing the ball to lose all its flexibility and become brittle.
No, it is actually tiny drops of liquid water. As Bill Nye the Science Guy explains, true water vapour is a completely invisible gas. The cloudy steam you can actually see is made of liquid droplets that have started to cool down and condense in the air!
No, we can get incredibly close, but never quite reach it. There is no way to completely separate an object from all sources of heat in the universe. Heat always finds a path to sneak back in, making Absolute Zero an idea rather than a place you can actually reach.
Understanding the Science
Tap each card to reveal the science behind solids, liquids, gases, and how they change from one state to another.
Key Concepts
Solid, Liquid, Gas
Tap to learn moreThese are the three main phases of matter. In a solid, molecules are packed tightly and hold their shape. In a liquid, they move faster and flow. In a gas, they move wildly and take the shape of their container.
Melting (Solid to Liquid)
Tap to learn moreAdding heat energy makes tightly packed molecules move faster and break out of their rigid structure. Bill Nye the Science Guy demonstrates this by melting solid metal into molten liquid bronze.
Freezing (Liquid to Solid)
Tap to learn moreRemoving heat energy slows molecules down until they lock into a rigid structure. We saw this when Bill Nye the Science Guy used a massive freezer to turn a bowl of liquid water into a solid ice popsicle.
Evaporation & Boiling (Liquid to Gas)
Tap to learn moreAdding even more energy makes liquid molecules move so fast they break apart entirely and become a gas. We saw this when liquid nitrogen absorbed heat from the room and boiled instantly!
Condensation (Gas to Liquid)
Tap to learn moreTaking heat energy away slows gas molecules down so they clump back into a liquid. This is what happens when invisible water vapour cools down in the air to form the cloudy drops we call "steam".
Sublimation (Solid to Gas)
Tap to learn moreSometimes a solid changes directly into a gas without becoming a liquid first. Bill Nye the Science Guy showed this by putting dry ice (solid carbon dioxide) into warm water, where it instantly turned into a bubbling gas to inflate a balloon.
Energy is the Key
Tap to learn moreThe only difference between solid steel, liquid steel, and steel vapour is the amount of energy. Adding heat energy makes molecules move faster. Taking heat away makes them slow down.
Absolute Zero
Tap to learn moreThis is the theoretical temperature where all molecular motion completely stops. It is colder than anywhere in the universe, and because heat always transfers from warmer areas, it is impossible to perfectly achieve.
Try It: States of Matter Basics
Heat, cool, and compress atoms and molecules to see how they change between solid, liquid, and gas phases.
Apply Your Knowledge
Now let us see if you can connect what you have learned to the real world.
Match the Concepts
Click an object to select it, then click the matching description to place it.
Real-World Challenge
Imagine you are an aerospace engineer designing a rocket fuel tank. The rocket needs to carry liquid hydrogen, which normally exists as a gas on Earth. Based on what you have learned about energy and phases of matter, what challenges will you face to keep the fuel in its liquid phase, and how might you solve them?
What Has Changed Since This Episode Aired
This episode of Bill Nye the Science Guy first aired in 1993. While the core science remains accurate, here are a few things that have been refined or expanded since then.
Updated: Today, physicists have reached temperatures that are billionths, or even trillionths, of a degree above Absolute Zero (picokelvins)! They achieve this not with traditional freezers, but by using lasers to slow down atoms.
Updated: While plasma is briefly mentioned in the song at the end of the episode, modern science classes officially teach Plasma as the fourth fundamental state of matter. In fact, plasma makes up the vast majority of the visible universe, including our sun and all the stars!
Test Your Understanding
Answer these questions and get instant feedback. How many can you get right?
Results
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Reflection
What surprised you the most about how extreme cold affects everyday objects? Can you think of a situation in your daily life where understanding phase changes is important?
I love this episode. I recommend watching it and I encourage recording your thoughts in the discussion box.