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Clingy Popcorn: Asking Questions About Electric Pull worksheet preview

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Clingy Popcorn: Asking Questions About Electric Pull

Grade 8 electric forces: turn clingy popcorn at a theater stand into testable questions, then use scale data on charge and distance to ask what changes the pull.

Grade 8ScienceInteractive · Printable

Aligned toMS-PS2-3

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What’s included

  • Single worksheet
  • Auto-graded online
  • 1 NGSS standard
  • Printable answer key
  • 10 questions
  • Classroom-ready

Details

Format
Interactive · Printable
Grade
Grade 8
Subject
Science
Question types
Fill in the blank, Multiple choice, Sorting, Short answer

About this worksheet

What students practice

  • Students write and sort testable questions about what affects the strength of an electric force.
  • Students use scale data to describe how the amount of charge and the distance change an electric pull.
  • Students ask follow-up questions from new observations of electric pushes and pulls.

How to use

Have students list their own questions about the clinging popcorn before reading paragraph 2, then compare their questions with the ones on the sheet.

Curriculum

NGSS standard covered

MS-PS2-3

Ask questions about what affects the strength of electric and magnetic forces, such as distance and current.

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Clingy Popcorn: Asking Questions About Electric Pull

Turn a concession stand puzzle into testable questions about electric force.

From a sticky scoop to testable questions

Read the notes, then answer the questions.

Concession Stand Notes: Why Does Popcorn Cling?

1On opening night of the Lakeview Community Theater's fall play, eighth graders Ines Valdivia and Kofi Brandt volunteered at the concession stand. The lobby air was dry, and whenever Kofi moved the stand's plastic scoop toward the popcorn, small flakes jumped up from about a centimeter away and clung to it. Ines noticed that the flakes jumped more often right after the scoop had been wiped with the stand's wool cleaning cloth. The stand manager, Ms. Marguerite Oduya, teaches physical science on weekdays. She said that the rubbed scoop was probably carrying an electric charge, and she challenged the pair to turn what they saw into questions they could test.

2The next week, in Ms. Oduya's classroom, Ines and Kofi built a test stand. A small foam ball wrapped in aluminum foil sat on a paper cup on a digital scale that reads to 0.01 g. They rubbed a plastic ruler with a wool cloth and clamped it in a holder right above the ball. When the charged ruler pulls up on the ball, the scale reading drops, so the size of the drop shows how strong the pull is. A drop of 0.20 g means the ruler pulls up on the ball with a force equal to the weight of 0.20 g. Before every trial, Kofi touched the ball with a finger to remove any leftover charge, and the pair used a fresh ruler from a set of identical rulers.

3In Test 1, they changed the number of rubs and always held the ruler 2 cm above the ball. In Test 2, they rubbed every ruler 10 times and changed the distance from the ruler to the top of the ball. They ran three trials for each setting and averaged the drops.

4They also wrote down two extra observations. First, a metal spoon held by its handle and rubbed 10 times with the wool cloth made no drop on the scale at all. Second, when Kofi hung a rubbed ruler from a thread and brought a second rubbed ruler near it, the hanging ruler swung away. It barely moved when the second ruler was 10 cm away, but it swung away sharply when the rulers were 3 cm apart.

1.
Which question could Ines and Kofi test, based on what Ines noticed at the stand?
  • A. Is a plastic scoop nicer to use than a metal scoop at a busy stand?
  • B. What made the theater pick a plastic scoop instead of a steel one?
  • C. Does wiping the scoop more times change how strongly it pulls on popcorn?
  • D. Why do people buy more popcorn on opening night than on other nights?
2.
Sort each question by what it asks about.
Does holding the ruler closer to the foil ball change the pull on it?Does a ruler rubbed 40 times pull harder than one rubbed 10 times?Do audience members like the popcorn better when it is warm?Does the pull drop if the ruler is raised from 3 cm to 6 cm above the ball?Does rubbing the ruler longer leave more charge on it, so the pull grows?Why do some people find small static shocks so annoying?
How distance affects the forceHow the amount of charge affects the forceNot about the strength of the force
3.
Use paragraph 3. Which variable did the pair keep the same in Test 2?
  • A. The size of the drop on the scale
  • B. The height of the ruler above the ball
  • C. The mass of popcorn in each bag
  • D. The number of rubs with the wool cloth

What the scale data show

Use the two tables and the notes to answer the questions.

Test 1: Ruler 2 cm Above the Ball
Rubs with wool clothAvg. drop on scale (g)
50.11
100.20
200.27
400.31
Test 2: Ruler Rubbed 10 Times
Distance to ball (cm)Avg. drop on scale (g)
10.80
20.20
30.09
40.05
4.
Use Test 2.

The pull at 1 cm is   times the pull at 2 cm.

5.
Which statement best describes the results of Test 2?
  • A. The pull grew as the ruler moved away, since the charge had more room.
  • B. The pull stayed near 0.80 g until the ruler was more than 3 cm away.
  • C. The pull fell by about the same amount for each extra centimeter.
  • D. The pull fell as the distance grew, and it fell fastest close to the ball.
6.
Which statement best describes the results of Test 1?
  • A. Each doubling of the rubs raised the pull, but by less each time.
  • B. The pull went down after 10 rubs, since the ruler wore out.
  • C. Each doubling of the rubs doubled the pull on the foil ball.
  • D. The number of rubs made little difference, since the distance stayed at 2 cm.
7.
Suppose a 0.15 g piece of popcorn feels the same pull as the foil ball. It jumps up to the ruler only when the pull is larger than its weight, a drop of 0.15 g. Use Test 2 (10 rubs).

The greatest distance in the table at which the piece would jump up is   cm.

8.
Use paragraph 4. The rubbed metal spoon made no drop on the scale. Which question would best follow up on this observation?
  • A. Would the spoon look shinier if it were rubbed with the cloth for longer?
  • B. Does the material of the rubbed object change how strongly it pulls on the ball?
  • C. Why do restaurants hand out metal spoons more often than plastic ones?
  • D. Is a metal spoon heavier than a plastic ruler of the same length?
9.
The hanging rulers in paragraph 4 pushed each other away. Suppose the pair put a rubbed ruler on the scale and held a second rubbed ruler 2 cm above it. What would most likely happen to the scale reading?
  • A. It would rise, because the ruler above would push down on the one on the scale.
  • B. It would drop, because a charged ruler pulls up on whatever sits below it.
  • C. It would stay the same, because the two rulers do not touch each other.
  • D. It would drop to zero, because the two charges would cancel each other out.
10.
Kofi now thinks the flakes cling to the scoop only because popcorn is greasy and sticky, not because of an electric force. Do you agree? Write a claim, give evidence from the notes and from both tests, and explain your reasoning. Then write one testable question that could check Kofi's idea, naming what you would change and what you would measure.

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