Film title: Changing state
To create the perfect snowman, the snow has to be in just the right condition: not too solid or it would be difficult to mould, not too liquid or it would be too wet and slushy.
Whether a substance is solid, liquid or gas is called the state of that material.
solid
liquid
gas
You might hear the term "states of matter".
states of matter
Matter can be changed from one state to another by heating or cooling.
When solids are heated, their molecules start to vibrate.
If they can obtain enough heat energy, the molecules vibrate so much that eventually they are able to move freely and the solid melts into a liquid.
melting
solid becomes a liquid
As the temperature rises above zero degrees Celsius, solid snow and ice melt into liquid water.
0°C
As a liquid gets even hotter, its molecules move about even more.
With enough heat, molecules near the surface of the liquid will change state.
They will evaporate and escape to become a gas.
evaporation
liquid changes to gas
When a liquid is heated, you may see bubbles of gas being produced.
At 100 degrees Celsius, liquid water turns into a gas called steam.
100°C
steam
Steam condenses into tiny water droplets and appears as a white mist.
But even a cool liquid will still evaporate if it absorbs enough heat from the surrounding air.
At temperatures below 100 degrees Celsius, water becomes an invisible gas called water vapour.
water vapour
That's why puddles don't last forever – they disappear as the rainwater evaporates.
So, to maintain the perfect snowman, he must be shaded from the Sun... or he will simply melt into a puddle and then evaporate into the air.
changing state
melting
evaporation
Whether a substance is solid, liquid or gas is called the state of that material.
solid
liquid
gas
You might hear the term "states of matter".
states of matter
Matter can be changed from one state to another by heating or cooling.
When solids are heated, their molecules start to vibrate.
If they can obtain enough heat energy, the molecules vibrate so much that eventually they are able to move freely and the solid melts into a liquid.
melting
solid becomes a liquid
As the temperature rises above zero degrees Celsius, solid snow and ice melt into liquid water.
0°C
As a liquid gets even hotter, its molecules move about even more.
With enough heat, molecules near the surface of the liquid will change state.
They will evaporate and escape to become a gas.
evaporation
liquid changes to gas
When a liquid is heated, you may see bubbles of gas being produced.
At 100 degrees Celsius, liquid water turns into a gas called steam.
100°C
steam
Steam condenses into tiny water droplets and appears as a white mist.
But even a cool liquid will still evaporate if it absorbs enough heat from the surrounding air.
At temperatures below 100 degrees Celsius, water becomes an invisible gas called water vapour.
water vapour
That's why puddles don't last forever – they disappear as the rainwater evaporates.
So, to maintain the perfect snowman, he must be shaded from the Sun... or he will simply melt into a puddle and then evaporate into the air.
changing state
melting
evaporation
Materials change state all the time, but how and why?
Learning points
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