Year 7 Science · Unit 3 · Lesson 12
Foundation Worksheet
Learning Goals
Fill the gap
Choose words from the word bank. Each word is used at most once. Two words are not needed: cross them out.
When two materials rub together, tiny charged particles called move from one material to the other, so each object gains an electric . Two objects with the same kind of charge each other, and a positive object and a negative object each other. The force between charged objects is the force. The force that pulls any two objects with mass together is the force, and it is stronger when the objects have more .
True or false? Fix the false ones
Circle T or F. If a statement is false, correct it on the line.
1. There are two kinds of electric charge: positive and negative.
Correct it:
2. Rubbing a balloon on your hair creates new charge out of nothing.
Correct it:
3. The electrostatic force can act across a gap, without the objects touching.
Correct it:
4. Gravity can pull objects together or push them apart.
Correct it:
5. A charged balloon sticks to a wall, so the wall must have been charged too.
Correct it:
6. The further apart two masses are, the weaker the gravitational pull between them.
Correct it:
1. Draw two diagrams. (a) A sphere marked + beside a sphere marked −. (b) Two spheres both marked −. On each sphere, draw an arrow for the electrostatic force, and label each diagram “attract” or “repel”.
Sort it
Decide which force is acting, and whether it attracts or repels. Write each situation in the correct box. The boxes do not hold the same number of items.
Electrostatic: attract
Electrostatic: repel
Gravitational
Read the data: the tissue test
Scenario: a charged ruler over tissue
Noah rubs a plastic ruler with a woollen cloth and holds it above 20 tiny bits of tissue on a desk. He counts how many bits jump up to the ruler at different heights. He re-rubs the ruler the same way before each test.
| Height above desk (cm) | 1 | 2 | 4 | 6 |
|---|---|---|---|---|
| Bits picked up (out of 20) | 14 | 9 | 3 | 0 |
Source: sample class results.
2. Describe the pattern in Table 1. What does it tell you about the electrostatic force?
3. At 6 cm, no bits jump up. Two non-contact forces act on each bit of tissue. Name both, say which way each acts, and explain why the tissue stays on the desk.
4. Zara rubs a balloon on her hair. When she lifts the balloon away slowly, strands of her hair rise up toward it. Explain how the balloon became charged and why her hair is pulled toward it.
Fill the gap
electrons; charge; repel; attract; electrostatic; gravitational; mass. Not used: colour and temperature.
True or false
1. True. 2. False: rubbing only moves electrons from one material to the other. 3. True. 4. False: gravity only ever attracts. 5. False: the wall is uncharged overall; the balloon pulls the wall’s unlike charges toward its surface, so they attract. 6. True.
Question 1
(a) An arrow on each sphere pointing toward the other sphere (1). (b) An arrow on each sphere pointing away from the other (1). Labels: (a) attract, (b) repel (1). [3 marks]
Sort it
Electrostatic, attract: a charged comb picking up bits of paper; cling wrap clinging to your hand; a rubbed balloon bending a stream of tap water. Electrostatic, repel: two straws swinging apart; hairs spreading apart. Gravitational: an apple falling; a waterfall; Earth keeping a satellite in orbit; a cricket ball dropping onto the pitch.
Read the data: the tissue test
2. The higher the ruler, the fewer bits it picks up: 14 at 1 cm, none at 6 cm (1). So the electrostatic force gets weaker as the distance increases (1). [2 marks]
3. Electrostatic force, pulling up toward the ruler (1). Gravitational force (weight), pulling down toward Earth (1). At 6 cm the electrostatic pull is weaker than the tissue’s weight, so gravity wins and it stays down (1). [3 marks]
Question 4
Marking guide: 1 rubbing moves electrons from one material to the other (it does not make charge); 1 the balloon gains electrons and becomes negative; 1 the hair loses electrons and is left positive; 1 unlike charges attract, so the hair is pulled toward the balloon; 1 the electrostatic force is non-contact, acting across the gap. [5 marks]
Model answer: Rubbing does not create charge; it moves electrons. Electrons move from Zara’s hair onto the balloon, so the balloon becomes negative and her hair is left positive. Unlike charges attract, so the hair is pulled toward the balloon. The electrostatic force is non-contact, so it acts across the gap before they touch.
Common error: “rubbing makes charge”. Rubbing moves charge that was already there.