Year 7 Science · Unit 2 · Lesson 1
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Learning Goals
Match each word to its meaning
Write the letter of the correct meaning next to each word. Each letter is used once.
| Word | Letter | Meaning |
|---|---|---|
| Matter | A. The pull of gravity on an object, measured in newtons | |
| Mass | B. How much space something takes up | |
| Volume | C. A glowing, electrically charged state of matter, as in lightning | |
| Weight | D. Anything that has mass and takes up space | |
| Plasma | E. The amount of matter in an object, measured in grams or kilograms |
1. What does it mean to say a gas can be compressed? Name one everyday object from the lesson that works by compressing a gas.
Classify and justify
For each sample, write its state (solid, liquid or gas) and one piece of evidence about its shape, its volume or what you can see.
| Sample | State | Evidence |
|---|---|---|
| A steel ruler | ||
| Honey poured into a jar | ||
| The helium inside a party balloon | ||
| A pile of dry sand | ||
| The white cloud you can see just above a boiling kettle’s spout |
Cause and effect: pressing the brake pedal
Fill the two empty boxes. Each box is caused by the one before it, and row 2 carries on from the end of row 1.
Read the data: working under the sea
Scenario
Divers who work deep underwater can be lowered in a diving bell, a sealed chamber on a cable. Engineers must work out how much breathing gas (oxygen mixed with helium) to pack into the bell’s tanks, because a gas can be squeezed into a much smaller volume. The seawater surrounding the bell is very nearly impossible to compress. To see the difference, a class sealed the ends of two syringes and pushed each plunger as hard as they could.
| Syringe holds | Volume before pushing (mL) | Volume while pushed (mL) |
|---|---|---|
| Air | 60 | 24 |
| Water | 60 | 60 |
Source: sample class results.
2. Calculate how many millilitres the volume of the air decreased by. Then give this decrease as a percentage of the starting volume.
Answer %
3. The breathing gas inside the bell and the seawater surrounding it are both matter. Give one piece of evidence for each that shows it has mass and takes up space.
4. Use Table 1 to explain why the engineers must calculate the amount of gas carefully, but do not need to allow for the seawater being squeezed into a smaller volume.
5. A solid keeps its shape, a liquid keeps its volume but not its shape, and a gas keeps neither. Explain why, using how close together the tiny bits of each state are. Give an everyday example of each state. Then explain why a pile of sand can be poured but is still a solid.
Match each word to its meaning
Matter → D; Mass → E; Volume → B; Weight → A; Plasma → C.
Question 1
Squeezed into a smaller volume (1). A bike pump (1). [2 marks]
Classify and justify
1 mark per row (state and evidence). Steel ruler: solid, fixed shape and volume. Honey: liquid, takes the jar’s shape but keeps its volume. Helium: gas, fills the whole balloon. Dry sand: solid, each grain keeps its own shape; pouring does not decide the state. Kettle cloud: liquid, tiny droplets of water; water vapour (gas) is invisible. [5 marks]
Cause and effect: pressing the brake pedal
Box 1: its particles are already touching, with almost no empty space between them (1). Box 2: so it is very nearly impossible to compress; its volume stays the same when it is pushed (1). [2 marks]
Read the data: working under the sea
2. 60 − 24 = 36 mL (1); 36 ÷ 60 × 100 = 60% (1). [2 marks]
3. Gas: a full tank weighs more than an empty one, and the gas fills the tank (1). Seawater: it can be weighed, and it fills its container (1). [2 marks]
4. The air’s volume fell by 60%, so a gas’s volume depends on how hard it is squeezed and the amount must be worked out (1). The water’s volume did not change, so seawater keeps its volume when pushed (1). [2 marks]
Question 5
Marking guide: 1 solid: bits locked close together, cannot move past each other, so fixed shape and volume; 1 liquid: bits touching but can slide, so the shape changes but the volume does not; 1 gas: bits far apart with lots of empty space, so no fixed shape or volume; 1 “fixed shape” and “fixed volume” used correctly; 1 a correct example of all three states; 1 sand pours, but each grain keeps its own shape. [6 marks]
Model answer: In a solid, such as a rock, the bits are locked close together, so it has a fixed shape and a fixed volume. In a liquid, such as milk, the bits touch but can slide past each other, so it takes its container’s shape but keeps a fixed volume. In a gas, such as the air in a tyre, the bits are far apart, so it has no fixed shape and no fixed volume. Sand pours, but each tiny grain keeps its own shape, so sand is a solid.
Common error: calling the kettle’s white cloud a gas; water vapour is invisible.