Year 3 Science: Hard, soft and permeable rocks
Part of the Year 3 Science rocks, fossils and soils chapter. Chapter overview · whole chapter on one page
Hard, soft and permeable rocks
A material is permeable if water can soak into it or pass through it. A material is impermeable if water cannot soak into it or pass through it.
A rock is hard if it does not crumble when you press it gently. A rock is soft if it crumbles.
To make a fair test, scientists use the same amount of water for each sample, and the same time limit. In the class test, each sample had 5 ml of water dropped on it, and the time was 60 seconds. The table shows the results.
| Sample | Colour | How it looks and feels | Layers? | Hard or soft? | Water soaks in? |
|---|---|---|---|---|---|
| A | dark grey | smooth | yes | hard | no, not within 60 seconds |
| B | white | crumbly | no | soft | yes, in 5 seconds |
| C | grey, with black and white dots | rough | no | hard | no, not within 60 seconds |
| D | light brown | gritty, with tiny grains | yes | hard | yes, in 20 seconds |
| E | red-brown | rough, with small holes | no | hard | yes, in 10 seconds |
| F | white | smooth and shiny, with thin lines | no | hard | no, not within 60 seconds |
Key ideas
- A material is permeable if water can soak into it or pass through it.
- A material is impermeable if water cannot soak into it or pass through it.
- A hard rock does not crumble when pressed gently. A soft rock crumbles.
- A fair test uses the same amount of water and the same time limit for every sample.
Method. Find the soft sample in the table.
- Read the column Hard or soft? Only one sample is soft.soft
- Name the sample. Sample B is soft.B
- Write the answer. B
Check. Sample B is also crumbly. ✓
Method. Look for the smallest number of seconds in the column Water soaks in.
- Read the column. Sample B soaked in after 5 seconds. D took 20 seconds, and E took 10 seconds.5 seconds
- Choose the smallest. The smallest time is 5 seconds, from sample B.B
- Write the answer. B
Check. Sample B is the fastest, at 5 seconds. ✓
Method. Read the row for sample A.
- Read the column Water soaks in? The table says no, not within 60 seconds.no
- Write the answer. So sample A is not permeable.no
- Write the answer. no
Check. Sample A is one of the samples that water did not soak into. ✓
Watch out
Watch out: hard does not mean impermeable. Samples D and E are both hard, and water soaks into both of them.
Try it at home or school (with a grown-up). Find a flat stone, or use a stone from home. Drip one small drop of water on it, and count the seconds until it soaks in or stays on top. Wipe the stone dry afterwards. Do not use hot water, and wash your hands at the end.
Exam tip
Grown-up tip. Ask: “Did the water stay on top, or did it soak in? How many seconds did it take?” Let your child say the word permeable, and explain what it means.
Exercise 7B Hard, soft and permeable rocks
Method. Look at the column Hard or soft?
- Read the column. Sample B is the only soft sample.soft
- Name the sample. So the soft sample is B.B
- Write the answer. B
Check. Sample B crumbles. ✓
Method. Look at the column Water soaks in?
- Read the column. Samples B, D and E have a time for water to soak in.B, D, E
- Write the answer. B, D, E
Check. Samples A, C and F did not let water soak in. ✓
Method. Look for 10 seconds in the column Water soaks in.
- Read the column. Sample E soaked in after 10 seconds.10 seconds
- Name the sample. So the sample is E.E
- Write the answer. E
Check. Sample D took 20 seconds, not 10. ✓
Method. Look for the rows that say no in the column Water soaks in.
- Read the column. Samples A, C and F say no, not within 60 seconds.A, C, F
- Write the answer. A, C, F
Check. Three samples did not let water soak in, and three did. ✓
Method. Read the definition at the start of this section.
- Read the definition. A material that water can soak into or pass through is permeable.permeable
- Write the answer. permeable
Check. The opposite is impermeable. ✓
Method. Read the definition at the start of this section.
- Read the definition. A material that water cannot soak into or pass through is impermeable.impermeable
- Write the answer. impermeable
Check. Impermeable starts with im, meaning not. ✓
Method. Look at the row for sample F.
- Read the column Water soaks in? The table says no, not within 60 seconds.no
- Write the answer. no
Check. Sample F is impermeable. ✓
Method. Look at the row for sample D.
- Read the column Hard or soft? The table says hard for sample D.hard
- Write the answer. yes
Check. Only sample B is soft. ✓
Method. Look for a hard sample that lets water soak in.
- Read the table. Samples D and E are both hard, and water soaks into both.D, E
- Decide. So a hard rock can be permeable, and Mo is not right.no
- Write the answer. No. Accept D or E, which are hard and let water soak in.
Check. Hard and permeable can both be true. ✓
Method. Think about the samples that are soft.
- Think about sample B. Sample B is soft and crumbly, and water soaked in after 5 seconds.5 seconds
- Make the prediction. So a new soft, crumbly sample is likely to let water soak in.yes
- Write the answer. Accept yes, because the soft, crumbly sample B soaked in quickly.
Check. A prediction is a guess based on evidence, and it can be tested. ✓
Method. Think about what makes a test fair.
- Think about the test. Only the sample should change. The water and the time must stay the same.same water
- Give one thing. For example, the same amount of water for each sample.same amount
- Write the answer. Accept any one of: the same amount of water, the same time limit, the same height for the drop.
Check. Changing one thing only makes the test fair. ✓
Method. Think about a safe way to press a stone.
- Think about the test. A soft stone crumbles when it is pressed gently.crumbles
- Describe the test. Press the stone gently with your thumb, and look for crumbs.press gently
- Write the answer. Accept any safe test, such as: press the stone gently with your thumb to see if it crumbles.
Check. Do not press hard, and do not use a stone that could cut you. ✓