>> Hello, everyone.
My name is Sultan Alneyadi,
and I'm an astronaut
living and working on board
the International Space Station.
Today, we are going to explore
the differences between
physical and chemical changes.
There are many different
chemical and physical changes
happening on board
the space station
at a given time.
Are you ready to explore
the station with me?
Let's get started.
A physical change is when...
For example, if we take
an ice cube and melt it,
a physical change has occurred.
The H2O molecules that make up
the liquid water are
the same H2O molecules
that made the solid ice cube.
As solid ice, the H2O molecules
are frozen in place
and can only vibrate.
Liquid water molecules are
able to move and flow around
each other.
A chemical change occurs...
Meaning that...
Generally speaking,
a chemical change cannot
be easily reversed.
There are six indicators
that tell us a chemical change
has occurred:
...or a solid.
Sometimes we refer
to chemical changes
as chemical reactions.
For example, the rocket
that brought me up to
the International Space Station
utilized a chemical reaction.
The engines of
the Falcon 9 rocket burned
kerosene and liquid oxygen
to generate enough thrust
to propel us upwards,
out of Earth's atmosphere.
Once ignited,
the rocket's engine produced
light, hot gas, and smoke
that you can see bellowing
out of the bottom of the rocket.
These all indicate
that a chemical change
has taken place.
On Station, the solid fuel
ignition and extinction,
growth and extinction limit,
or SoFIE-GEL investigation
studies burning in microgravity.
These experiments will help to
determine how fuel temperature
affects material flammability.
The result of this study would
help us to better understand
fire safety and separation
in space and on Earth.
A good example
of a physical change
is when we add water
to our dehydrated food in space
because this is
totally reversible
by removing the water.
And once eaten, this is
a chemical change, because
the acid in our stomachs
breaks down the food and changes
its chemical composition.
Another example of
a physical change is
when we cut our hair in space.
And this is a physical change
because the composition
of the hair has not changed.
Once the hair is cut,
it is still hair.
There are no indications that
a chemical change has occurred.
Can you think of other examples
of physical and chemical changes
back on Earth?
To learn more
and experiment with physical
and chemical changes,
check out the corresponding
classroom connection online.
Thank you for exploring
science with me today,
and see you soon.