# Matter and its three states

Your child learnt these properties of matter:

1) Solid has fixed shape and volume

2) Liquid has no fixed shape but it has a fixed volume

3) Air has no fixed shape and volume.

Air can be compressed.

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Let’s apply the science knowledge into this question.

__Study this diagram__

The capacity of the container below is 400cm^{3}. It contained 100cm^{3} of water.

Please follow the sequence in each question.

__Question 1__

David added 150cm^{3} of rocks into the container. What was the final volume of the container?

**The final volume is 400cm ^{3} **

Why?

The rocks are in solid state. They have a fixed volume and cannot be compressed.

Water has a fixed volume and they cannot be compressed.

When the rocks are added, the rocks **displace** the air inside the container. As the air cannot escape, the air is compressed.

__Question 2__

After David has added the rocks, he pumps in 60cm^{3} of air into the container using the air pump.

What is the final volume of air?

We have to get the answer using mathematics.

Volume of container = 400cm^{3}

Volume of rocks = 150cm^{3}

Volume of water = 100cm^{3}

**Volume of air = 400 – 150 – 100 = 150cm ^{3}**

We **do not** add in the 60cm^{3} of air.

Why?

Air has no fixed volume. The air can be compressed and will occupy the remaining space inside the container.

__Question 3A__

Next, David then removes 50cm^{3} of water by turning on the tap. What is the final volume of water?

**100cm ^{3} – 50cm^{3} = 50cm^{3}**

__Question 3B__

What is the final volume of air after David removes 50cm^{3} of water based on Question 3A?

Answer: Take 150cm^{3} of air from question 2, add 50cm^{3}.

**150 + 50 = 200cm ^{3} of air.**

Why do we add the volume of air?

**Take note:**

You’ve learnt this in school: Air **does not** have a fixed volume. Air can be compressed.

Many students have the assumption that **no** **fixed volume** means air can only be compressed. That is **wrong**!

Actually, no fixed volume means the air will occupy the **remaining** space in the container!

**Add this Science Knowledge today**: Air will ** always occupy the remaining space inside the container**.

For this question, after the rocks and water have occupied the space inside the container, whatever remaining space inside the container belongs to air.

Hence, if you remove 50cm^{3} of water, the volume of water ** removed** belongs to the volume of air inside the container.

The same concept applies when you remove rocks. If you remove 50cm^{3} of rocks, that volume of rocks ** removed** belongs to the volume of air inside the container.

__Question 4__

Finally, David decides to remove 30cm^{3} of air. What is the final volume of air?

**Answer: 200cm ^{3}** (same answer as question 3B)

Why?

Air has no fixed volume. Air will ** always occupy the remaining space inside the container**.

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**Talk again soon!**

**Andy Ling**

**Simplifying science concepts for your child**

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## stoopid_potatohead

i hve my sci exam tmr n this helped a lot:D tyy <3

## scienceshifu

Thank you!