Curious Kids is a series for children of all ages. If you have a question you’d like an expert to answer, send it to CuriousKidsUS@theconversation.com.

How do ice cubes cool a drink? – Helen, age 12, Boston, Massachusetts

I like to make my own iced tea. First, I steep about a quart of terrifically strong hot tea and pour it into a pitcher loosely filled with ice cubes straight from the freezer. The result is about two quarts of delicious, cold tea, with a few ice cubes floating on top.

What’s the science behind my perfect pitcher of iced tea? A simple answer is that the near-boiling tea transferred its hotness to the below-freezing ice cubes. This transfer raised the temperature of the ice cubes so that much of the ice melted. That both cooled the tea to a refreshing drinking temperature and diluted it for a proper taste.

My iced tea process reminds me of physics experiments I worked on that flew on the space shuttle Columbia in the 1990s. I was interested in how liquids turn into solids in the absence of gravity.

Both those space experiments and the making of iced tea depend on liquids or solids getting hotter or colder in just the right combination. The explanation for how it all works depends on two related concepts: temperature and energy.

What are temperature and energy?

The concept of temperature grew out of the sense of what feels hot and cold to human touch. Boiling water is too hot to touch safely, and a candle flame is even hotter. Ice cubes feel cold. A thermometer is a special hotness meter that more reliably and repeatably determines the degree of hotness or coldness of substances than our sense of touch.

Eighteenth-century physicist Daniel Gabriel Fahrenheit defined the point when ice melts or water freezes as 32 degrees of temperature – what we we now call 32 degrees Fahrenheit in his honor. He also defined the temperature at which water boils and turns into steam to be 212 degrees F.

Energy is a more complicated concept. One way to think about energy is as a way to track what it costs nature to makes changes from one set of conditions to another. There are many types of energy. Thermal energy is related to temperature. Kinetic energy is based on how fast stuff is moving. Other forms of energy include, to name only a few, electromagnetic energy, chemical energy and nuclear energy.

Another type of energy is called potential energy and it accounts for the energy stored by the forces acting between or within objects. It is those forces that control the transfers from one type of energy to another. Examples of potential energy that you can see are a rubber band stretched and about to snap back or a boulder sitting at the top of an incline, ready to roll. On a microscopic level, potential energy is composed of all the interacting forces between the atoms and molecules that make matter.

Once a boulder begins to roll down the hill, its potential energy from the force of gravity first transforms to kinetic energy and then maybe to thermal energy or to the work of knocking down a tree. Although energy can transform from one type to another, the total amount of energy always remains the same. Whatever amount of energy is gained in one place must be lost from somewhere else. Scientists call this rule of nature conservation of energy, or in cases involving thermal energy, the first law of thermodynamics.

On a molecular level

As an example of the distinction between energy and temperature, compare a cup of hot tea and an iceberg. The hot tea is clearly at a much higher temperature than the iceberg, but the large iceberg has vastly more energy than the tiny cup of tea.

The tea is hotter than the iceberg because the molecules that make up the tea are moving faster than the molecules that make up the iceberg. The temperature is essentially the average energy of the molecular movements.

The speed and energy of a typical single liquid molecule are greater than for a typical single iceberg molecule. But the iceberg has many, many more molecules, all moving around, interacting with each other and transferring vast amounts of energy between their kinetic and potential energies.

The trick is energy transfer

Back to the question of making iced tea. When the hot tea encounters the ice cubes, the molecules of tea-flavored water collide with the molecules on the surface of the ice. The liquid’s molecules slow down. The ice’s molecules speed up, and some even leave the solid and mix in with the liquid tea.

The tea loses thermal energy and lowers its temperature. That energy transfers to the ice, which gains that energy and increases its temperature.

The process of energy moving from one place to another due to differences in temperature is called heat transfer. Left to itself, nature transfers thermal energy only from higher to lower temperatures. That observation is called the second law of thermodynamics. It’s why you will never see a cup of cold tea turn into a cup of ice cubes and hot tea.

In my pitcher, this process continues until the ice eventually reaches a temperature of 32 degrees F, its melting temperature. At that point, the ice cannot take any more energy and stay solid, even though it is still absorbing thermal energy from the hotter tea. Instead, any additional thermal energy absorbed by the 32 degrees F ice transforms it into 32 degrees F water.

Heat transfer cooling means that energy leaves the tea. Conservation of energy means a matching amount of energy raises the temperature of the ice to 32 degrees F and then turns some of that ice into 32 degrees F water. Thus the thermal energy of the tea turns into the potential energy of the water molecules that used to be part of the ice, lowering the temperature of the liquid in the pitcher. The process continues until eventually all the tea and whatever ice that survived the melting are at the same refreshing 32 degrees F.

Keep all this in mind as you enjoy your ice-cold drink on a hot summer day. Don’t dawdle, though, as the air temperature in the room or your warm hand on the glass can transfer their thermal energy to melt the rest of the ice and then begin to raise the temperature of your drink!

Hello, curious kids! Do you have a question you’d like an expert to answer? Ask an adult to send your question to CuriousKidsUS@theconversation.com. Please tell us your name, age and the city where you live.

And since curiosity has no age limit – adults, let us know what you’re wondering, too. We won’t be able to answer every question, but we will do our best.

Matthew Koss, Professor of Physics, College of the Holy Cross

This article is republished from The Conversation under a Creative Commons license. Read the original article.

Curious Kids is a series for children. If you have a question you’d like an expert to answer, send it to curiouskids@theconversation.edu.au You might also like the podcast Imagine This, a co-production between ABC KIDS listen and The Conversation, based on Curious Kids.

Why are there waves? - Evie, age 5.

Thanks for a great question, Evie.

When you look at the waves breaking at the beach, those waves might be at the end of a long journey. The waves might have been created thousands of kilometres away, or they could have been created near you.

There are lots of types of waves in the ocean, but the waves you usually see at a beach are created by the wind. When the wind blows over a smooth ocean, it creates little waves or ripples on the surface. If the wind continues to blow, the waves grow bigger.

Faster, bigger, longer

The faster the wind blows (like in a strong storm out at sea), the bigger the waves will grow.

The further the wind blows (or the bigger the area of the storm), the bigger the waves will grow.

And the longer the wind blows (like in a storm that lasts a long time), the bigger the waves will grow.

If the wind stops, or changes direction, the waves will stop growing, but they won’t stop travelling.

They will keep travelling away from where they were created in a straight line, sometimes for days, until they run into something like a beach where they are stopped because they break. That’s why there are still waves at the beach, even when it is not windy.

Waves trip over themselves

Imagine you were running really quickly. But then suddenly, you ran into thick gloopy mud. Your feet would slow down, but the top half of your body would still be going fast. You’d trip over.

Waves do the same thing and that is when they break.

As waves approach the shore, the water is shallower, and the bottom of the wave starts to feel the sand and rocks and seaweed. The bottom of the wave slows down, and soon, the top of the wave is going faster than the bottom part of the wave, so the top spills forward and topples over in a big splash.

Waves can travel a long way

Scientists who study the ocean (called oceanographers) have measured waves created in the Southern Ocean, and seen them travel all the way across the Pacific Ocean and break on the beaches of North America more than a week later.

Try counting the seconds between waves breaking on the beach. If the time between waves is 10 seconds or more, the waves have come from a long way away. If the waves were created nearby, the time between waves will be short, perhaps five seconds or fewer.

Sometimes when we look at the sea we might see different waves (some big, some small) all happening at the same time. These waves were created at different places, perhaps by different storms, but ended up in the same spot at the same time.

Freak waves

During big storms, waves can get very big. If big waves from two different storms meet together, that can create enormous waves that we call “freak waves”. The largest waves measured are around 25 metres high (that’s five giraffes standing on top of each other!) and they can tip over ships.

Hello, curious kids! Have you got a question you’d like an expert to answer? Ask an adult to send your question to curiouskids@theconversation.edu.au

Please tell us your name, age and which city you live in. We won’t be able to answer every question but we will do our best.

Mark Hemer, Senior Research Scientist, Oceans and Atmosphere, CSIRO

This article is republished from The Conversation under a Creative Commons license. Read the original article.

Curious Kids is a series for children in which we ask experts to answer questions from kids. You might also like the podcast Imagine This, a co-production between ABC KIDS listen and The Conversation, based on Curious Kids.

I am wondering: is dew the same as rain? What is dew? Thank you – Leo, age 3.

Great questions, Leo!

I am a plant ecologist, and rain and dew are things I need to understand. Plant ecology is all about learning how plants are affected by the world around them (their environment) in the same way that you are affected by your environment.

For example, if you go outside you might consider putting a hat on so you don’t get burnt by the hot sun. Or you might put a coat on so you don’t get cold or wet. Plants are greatly affected by water, whether it comes from dew or rain. So are rain and dew the same?

Dew is the water droplets that we find in the morning on leaves and other things outside, and usually in spring or winter when the air is cold. It is similar to rain because it forms from condensing water vapour. I hear you asking, “…but what does condensing water vapour mean?”. I will try to explain.

Water can be a liquid (we drink liquid water), it can also be a solid (think of ice cubes), and it can be a gas, which we call water vapour. When water warms up enough it breaks into small, fast-moving parts, called molecules. It changes from being a liquid to a gas – water vapour – that floats about in the air.

Think about how the steam (which is water vapour) from your hot bath floats about your bathroom.

So, now you understand what water vapour is and how it is made, think about what will happen if the fast moving water vapour cools down: this will help you understand condensation.

As the vapour cools, it slows down. The small parts, the molecules, start to gather together, especially on cold things (like a cool leaf) or in cold areas (like high in the sky). Scientists would say the water condenses.

If enough water molecules gather together (like a little water molecule “meeting”) they form a droplet of liquid water.

This same process (condensation) occurs when the steam from your hot bath condenses on the cold bathroom mirror – have you ever drawn a face on it?

Whether the droplets that form are dew or rain depends on where they formed.

Rain forms from water vapour condensing high in the sky as clouds. If enough water molecules gather together, it will get too heavy to stay in the sky and fall down on your head as rain.

Dew forms from water vapour that condenses on cold surfaces on the ground, like grass or a car on a cool morning (it usually gets a bit cooler early in the morning).

All plants need water and so do we – it is very precious to all life! Most plants get their water from the soil, but this water originally fell as rain and then soaked into the soil.

Some plants and lichen (lichen are like plants) can absorb water from dew. It’s a little bit like they are “drinking” the dew.

I hope this helps.

Hello, curious kids! Have you got a question you’d like an expert to answer? Ask an adult to send your question to curiouskids@theconversation.edu.au

Please tell us your name, age, and which city you live in. We won’t be able to answer every question but we will do our best.

Dylan Korczynskyj, Associate Professor, University of Notre Dame Australia

This article is republished from The Conversation under a Creative Commons license. Read the original article.

Curious Kids is a series for children. If you have a question you’d like an expert to answer, send it to curiouskids@theconversation.edu.au You might also like the podcast Imagine This, a co-production between ABC KIDS listen and The Conversation, based on Curious Kids.

Can snails fart? Thank you. – Avalon, age 9, Scotts Head, NSW.

Lots of animals fart because of what they eat, but it was not easy for me to find a clear answer on whether snails really do. More research is needed to know exactly how the digestive system of a snail really works.

You might have heard about methane. It is a gas found in a lot of animal farts. I did find one study that said that scientists kept some snails in a glass container for one day and one night and checked if they would produce methane. And the snails did not.

(For the adults in the audience, the paper noted that, “In this aspect, the structure of the microbiota and in consequence the functioning of the digestive microbial ecosystem of the snails differs markedly from those of vertebrates, especially herbivores.”)

You may have seen reports that scientists built a database showing which animals do and don’t fart. Not every animal in the world is on there, but it does say that mussels and clams (which, like snails, are part of a group of animals called molluscs) do not fart. Moon snails, which live in the sea, were also listed as a no.

One thing I can tell you is that a snail’s bottom is right over its head. This is because snails are very different from other molluscs (which includes things like octopus and squid as well). Because they are squashed into a protective shell, their body is twisted round to fit in. As a result, their bottom is just above and to the side of where their head comes out.

Gassy molluscs

Water snails, mussels and other molluscs do produce a gas called nitrous oxide if they live in polluted water.

You might have heard of nitrous oxide. It’s also called “laughing gas”. But this can be a problem, as nitrous oxide is a greenhouse gas and lots of it will add to climate change.

These mussels, when they are not producing laughing gas, produce something called “pseudo-faeces” which literally means “false poo”. Because the food they eat (little plants and animals floating in the water which they suck in) can contain a lot of sand, they sometimes have to squirt it all out. This doesn’t come out of their bottom, but out of something called a siphon, through which they suck their food.

Hello, curious kids! Have you got a question you’d like an expert to answer? Ask an adult to send your question to curiouskids@theconversation.edu.au

Please tell us your name, age and which city you live in. We won’t be able to answer every question but we will do our best.

Bill Bateman, Associate professor, Curtin University

This article is republished from The Conversation under a Creative Commons license. Read the original article.

Curious Kids is a series for children. If you have a question you’d like an expert to answer, send it to curiouskids@theconversation.edu.au You might also like the podcast Imagine This, a co-production between ABC KIDS listen and The Conversation, based on Curious Kids.

Who was the first ancient mummy wrapped up? - Jake, age 5, Swansea.

The first mummy to be wrapped up comes from the Chinchorro culture of South America, in the area of southern Peru and northern Chile. The oldest of these mummies was a person who died in 5050 BC, over 7,000 years ago. These Chinchorro mummies are 2,000 years older than the mummies in ancient Egypt!

One of these Chinchorro mummies was preserved by nature, and was not wrapped up, and it is 9,000 years old (meaning it is from 7,020 BC).

Chinchorro means “gill netters”, which is their way of fishing with nets. The Chinchorro people lived by the sea, the Atacama Coast, along the Pacific Ocean. Most of what they ate was seafood (fish and shellfish), sea birds and sometimes sea lions. They also hunted animals for meat and collected some plants, too.

Pictures of these mummies may frighten some curious kids. Parents are advised to search and look at images online before showing them to children.

These mummies have remained the same until today because the place where the Chinchorro lived was very dry, even though they lived by the ocean. Much of this area is a desert and some areas have not had rain in over 400 years!

How are Chinchorro mummies made?

The Chinchorro had different ways of preserving (to keep safely so that it does not spoil) the dead bodies. They would start by removing all the organs inside the body, even the brain. The hair and skin would also be removed using stone tools, not metal knives. Some of the sharpest knives were made using a pelican’s beak.

Sometimes, the head, arms and legs would be removed and the body was put back together later. The body would be dried out using a mixture of hot coals from a fire, as well as ash. They would place sticks inside the body to keep the body stiff and fill the insides with straw and feathers. The face would be covered in clay and left out to dry for 30-40 days. Sometimes the bodies would be painted red or black.

How did the Chinchorro mummies die?

Some of these bodies had diseases and broken bones. Arthritis and bone decay are two common diseases. Some mummies have damage in their ears suggesting that some people may have been deaf. This damage likely came from diving in the ocean for shellfish. Many mummies have broken bones that have gotten better. These injuries are either from accidents at work or fighting inside the community.

All sorts of people were made into mummies - men, women and children, young and older people, too. Even some babies were mummified, which could be because they died during childbirth; these babies were some of the most decorated mummies.

After the mummy was finished, it was not buried. People would put them in their houses and other places where people lived, worked and played. Some people think the mummies brought good luck.

We are not exactly sure why the Chinchorro made these mummies but we think it is because they cared for their dead families and wanted to keep their physical body, and their memory, alive forever.

Hello, curious kids! Have you got a question you’d like an expert to answer? Ask an adult to send your question to curiouskids@theconversation.edu.au

Please tell us your name, age and which city you live in. We won’t be able to answer every question but we will do our best.

Serena Love, Honorary Research Fellow, The University of Queensland

This article is republished from The Conversation under a Creative Commons license. Read the original article.