C. Matter and Energy · Properties of and Changes in Matter

Physical Changes: Same Stuff, New Look

C2.4 A1.2 A1.5About 40 minutes

Learning goals

I can explain that a physical change changes the state, volume or form of matter but does not make a new substance.
I can give examples of physical changes, including dissolving.
I can tell which physical changes are easy to reverse and which are not.

Words to know

physical change
A change in the state, volume or form (shape or size) of matter that does not make a new substance.

substance
One particular kind of matter, like water, sugar or aluminium.

form
The shape or size of a piece of matter.

dissolve
To mix completely into a liquid so you can no longer see the pieces, like sugar in water. The sugar is still there.

reversible
Able to be changed back. Melting ice is reversible: you can freeze the water again.

Is it still the same stuff?

Crumple a sheet of paper into a ball. Is it still paper? Yes! It just has a new shape. Tear it into pieces. Still paper! You made a physical change.

A flat sheet of white paper, a crumpled paper ball and a pile of torn paper pieces lie on a wooden table. — Flat, crumpled or torn, it is all still paper. Only the shape and size changed, so these are physical changes. AI-generated image

What is a physical change?

A physical change changes how matter looks, but it is still the same substance. No new substance is made.

Physical changes change matter's:

State: ice melting into water, water freezing, water evaporating. It is still water (H₂O, if you have seen that name).
Volume: air squeezed into a bike tire; a puffy air mattress letting its air out; water taking up more space when it freezes into ice (that is why a full water bottle can split in the freezer).
Form (shape or size): cutting, tearing, crushing, folding, bending, stretching, grinding, chopping. A crushed pop can is still aluminium. Chopped carrots are still carrots.

Three kinds of physical change: state (ice melts), volume (air is squeezed into a ball) and form (paper is crumpled). In each one, it is still the same substance.

Dissolving and mixing are physical changes too

Stir sugar into water. The sugar seems to disappear, but it is still sugar. Taste a drop of sugar water (in the kitchen, not in a science test) and it is sweet. If you let all the water evaporate, the sugar crystals are left behind.

Mixing trail mix, or mixing sand and water, is also a physical change. Each part is still the same substance, and you could separate them again.

Dissolving is a physical change. The salt seems to vanish in the water, but when the water evaporates, the salt crystals are left behind.

Physical change	What changed?	Still the same substance?
ice cube melting	state	yes, water
water freezing in a plastic cup	state and volume	yes, water
pumping air into a ball	volume (air squeezed in)	yes, air
sawing a log into firewood	form (size)	yes, wood
crushing a pop can	form (shape)	yes, aluminium
dissolving salt in water	the salt mixes into the water	yes, salt and water

Examples of physical changes.

Easy to reverse, or not?

Some physical changes are easy to reverse (undo):

Melted ice can be frozen again.
Salt dissolved in water can be recovered by evaporating the water.
A squeezed sponge springs back.

Some physical changes are hard or impossible to reverse, but they are still physical, because no new substance is made:

You can't un-cut a haircut, but the hair is still hair.
You can't un-crush a pop can perfectly, but it is still aluminium.
You can't un-tear paper, but the pieces are still paper.

The real test is not "Can I undo it?" but "Is it still the same substance?"

Worked example

Let's decide: is it a physical change?

Decide for each: sharpening a pencil, a snowman melting, dissolving a drink crystal in water.

Sharpening a pencil: the wood and graphite are cut into shavings. Still wood and graphite → physical change (form). Can't be undone, but still the same substances.
A snowman melting: solid water becomes liquid water → physical change (state). It could freeze again.
Dissolving drink crystals: the crystals mix into the water. They are still there (the water tastes sweet and has colour) → physical change. Evaporate the water and the crystals' sugar and colour are left behind.

All three are physical changes: no new substance is made.

Just for fun

What did one ice cube say to the other?

"I've been through a lot of changes, but deep down I'm still the same old water!"

Hands-on activity

Physical change lab

You need: a sheet of scrap paper, a small clear plastic cup, a marker or tape, salt, a spoon, warm tap water (a grown-up turns on the tap), a dark-coloured plate or a shallow dish, a sunny windowsill, a magnifying glass if you have one, paper and pencil.

Part 1: Form. Fold, crumple and tear the paper. After each change, ask: Is it still paper? Record.

Part 2: Volume when water freezes. Fill the plastic cup about half full of water. Mark the water level with the marker or a piece of tape. Put it in the freezer overnight. The next day, compare the top of the ice with your mark.

Part 3: Dissolve and recover. Stir 1 teaspoon of salt into 4 tablespoons of warm tap water until you can't see it. Pour a thin layer onto the dark plate. Leave it on a sunny windowsill for a few days. Look with a magnifying glass.

Share: for each part, tell someone: What changed (state, volume or form)? Was a new substance made?

What to look for: the paper is still paper; the ice is higher than the mark (water takes up more space when it freezes); salt crystals appear on the plate once the water has evaporated, so the salt was there all along.

Safety: use a plastic cup in the freezer, never glass (it can crack). Don't taste anything in the experiment. Only a grown-up uses hot water from a kettle or stove.

Your turn

What is a physical change?

Name the three kinds of things a physical change can change.

Is cutting an apple into slices a physical change? Explain.

Is dissolving sugar in water a physical change? How do you know?

Give one physical change that is easy to reverse.

Give one physical change that is hard to reverse.

More practice: warm-up

Physical change? Folding a paper airplane.

Physical change? Ice melting.

Physical change? Squeezing toothpaste out of a tube.

Physical change? Crushing a cracker into crumbs.

Does a physical change make a new substance?

More practice: on your own

Why can a glass bottle full of water crack in the freezer?

Which part of a physical change is shown when air is pumped into a basketball?

Sam says, "Sawing a log can't be undone, so it isn't a physical change." Is he right? Explain.

How could you get salt back after dissolving it in water?

In the lab, the ice ended up higher than the mark. What does that show?

Challenge

Melting chocolate and pouring it into a heart-shaped mould: name all the physical changes.

Sugar dissolves faster in warm water than in cold water. Design a fair test to show this.

Why is "Can I undo it?" not the best test for a physical change?

Check your understanding

Quiz

A physical change...

Which is a physical change?

When water freezes, its volume...

Dissolving salt in water is a physical change because...

Which physical change is hard to reverse?

Pumping air into a tire changes the air's...

For parents and teachers

Big idea: Ontario Grade 5 expectation C2.4 asks children to describe physical changes in matter as changes of state, volume or form that do not result in the formation of a different substance. The lab includes measurement and observation (A1.2) and sharing results (A1.5).

How to help: When cooking, ask "Physical change or not? Is it still the same stuff?" Chopping, grating, melting butter and dissolving sugar are all physical.

Common difficulties:

Thinking "irreversible" means "chemical". Cutting and tearing can't be undone but are physical.
Thinking dissolved sugar is gone. Taste (in cooking) or evaporation shows it's still there.
Forgetting volume changes. Freezing water and squeezing air are good examples.

Safety: use plastic, never glass, in the freezer. Grown-ups handle hot water. No tasting in the experiment.