Charging Plastic Wrap
•
20 minutes
Pairs
Objectives
• Students recognize that like charges repel and opposite charges
attract.
• Students use observations to predict how charged materials will
interact.
Teaching Tip
Step 1: Not all plastic wraps
hold a static charge. Most brand
name plastic wraps work. If not
using plastic wrap provided in
the kit, test the plastic wrap in
advance.
Materials
For each pair
1
1 pc.
Inquiry Focus
• Predict
*paper towel
plastic wrap (30 cm x 15 cm)
For the teacher
1 pc.
plastic wrap (30 cm x 15 cm)
*Not provided in kit
1. Students observe a neutral object.
Distribute materials to each pair. Hold a piece of plastic
wrap as shown. Have students do the same and observe.
A How to make a plastic wrap tent
2. Students observe that opposite charges attract.
Tell students to lay the plastic flat on a desk. Have them
rub the plastic with a paper towel several times. Explain
that as the paper towel is rubbed over the plastic wrap,
the paper towel loses electrons and the plastic wrap
gains them. Ask: What charge does the plastic wrap
have after being rubbed by the paper towel?
(a negative charge) Tell students to pick up one corner
of the plastic wrap and observe what happens. (The
plastic wrap sticks to their hands.) Ask: If the plastic
wrap has a negative charge, what charge does
the skin of your hand have? (Since opposite charges
attract, the hands have a positive charge.)
3. Students observe that like charges repel.
Have students again lay the plastic wrap on the desk and
rub it with the paper towel. Tell them to pick up the plastic wrap in the middle so it again forms a tent shape. Ask:
How do the two sides of the plastic wrap act? (They
repel.) What can you infer from this observation?
(Both sides of the plastic wrap are negatively charged.)
SECTION 1 STATIC ELECTRICITY • 7
Charging Plastic Wrap (continued)
4.Discuss students’ observations.
Explain to students that objects that are electrically charged
interact in predictable ways. These interactions can be summarized as: Like charges repel and opposite charges attract.
Assessment
Have students predict what will happen if they
place a hand between the two sides of the charged
plastic wrap. (Likely predictions: The plastic wrap will be
attracted to the hand.) Have students test their prediction
and explain their observations.
Share with Your Students
The Electrostatic Series
Name
Date
STUDENT RESOURCE PAGE 1.4
INFORMATION SHEET
Electrostatic Series
+
2. Point out the + and – signs on the worksheet. Explain
that objects higher on the list give up electrons and
become positively charged when rubbed by other
objects. Objects lower on the list gain electrons and
become negatively charged. Ask: If you rub a piece
of wool against a rabbit, what charge does the
rabbit’s fur have? (a positive charge) What charge
will a balloon have if you rub it with a piece of
wool? (a negative charge)
rabbit’s fur
glass
nylon
wool
cat’s fur
Copyright ©Houghton Mifflin Company. All Rights Reserved.
silk
paper
cotton
plastic bags
balloon
plastic wrap
–
ELECTRICITY • SECTION 1 STATIC ELECTRICITY • 17
Student Resource Page 1.4 (p. 17)
+
+
+
+
A Petting a rabbit gives the
rabbit’s fur a positive charge.
8 • EXPERIENCE SCIENCE
1. Display the transparency Electrostatic Series. Explain
that this list compares the strengths of the charges
produced by rubbing objects together.
3. Tell students that the farther apart two objects are
on the list, the stronger the charge they take on. For
instance, a piece of glass becomes positively charged if
rubbed with a piece of plastic wrap. Ask: What charge
does the plastic wrap have? (negative) Explain that
the charges on both objects are strong because these
two materials are far apart on the list.
4.Have students find rabbit’s fur and glass on the list.
Explain that if glass is rubbed with rabbit’s fur, the fur
loses electrons to the glass. Ask: What charge does
the fur have? (positive) The glass? (negative) Point
out that while each object is charged, the charges are
weak because rabbit’s fur and glass are so near each
other on the list.
Measuring Static Charge
Name
Date
Electrostatic Series
Pairs
Objectives
• Students predict which of several different materials will
produce the strongest charge on a balloon.
+
rabbit’s fur
• Students construct a bar graph of their results.
glass
nylon
wool
cat’s fur
Copyright ©Houghton Mifflin Company. All Rights Reserved.
30 minutes
STUDENT RESOURCE PAGE 1.4
INFORMATION SHEET
silk
Materials
For each pair
Student Resource Pages
• 1.4 Electrostatic Series
1
balloon, small
• 1.5 Measuring Static Charge
1
millimeter ruler
• 1.6 Graphing Static Charge
paper
•
cotton
plastic bags
balloon
*objects to rub against
balloon (glass, nylon, silk,
cotton)
Inquiry Focus
• Measure
1 tsp. pepper
plastic wrap
–
1 pc. *white paper
1 pc.
ELECTRICITY • SECTION 1 STATIC ELECTRICITY • 17
Student Resource Page 1.4 (p. 17)
wool cloth
For the teacher
1
balloon, small
1
millimeter ruler
1 tsp. pepper
1 pc. *white paper
*Not provided in kit
Teaching Tip
Step 1: Before students carry
out the experiment, provide them
with objects of known lengths to
measure. Assess each student’s
ability to measure accurately in
millimeters.
1. Distribute the Resource Pages and materials.
Copy and distribute Student Resource Pages 1.4,
Electrostatic Series, and 1.5, Measuring Static Charge.
Have students read the entire Measuring Static Charge
Resource Page before beginning the experiments.
Distribute materials to each pair.
2. Students plan their experiments.
Have each pair of students blow up one balloon. Tell
them to fill the balloons about half-way (to medium)
only. Then discuss the experiment and what materials
students want to rub on the balloon. Tell students to
review Student Resource Page 1.4, Electrostatic Series,
as they make their predictions.
SECTION 1 STATIC ELECTRICITY • 9
Measuring Static Charge (continued)
Name
3. Demonstrate how to make measurements.
Use the setup shown to demonstrate how to use the
ruler to make the required measurements. Explain to
students that they may hear the pepper being attracted
to the balloon before they see this movement. Tell
students to lower the balloon slowly, stopping as soon
as an interaction between the pepper and the balloon is
observed. Have students read the measurement on the
ruler to find the distance between the paper and the
bottom of the balloon in millimeters.
Date
STUDENT RESOURCE PAGE 1.5
ACTIVITY SHEET
Measuring Static Charge
1 Choose four materials you will use to rub the balloon. List
them in the table.
1
2 Sprinkle about 2 teaspoon of pepper on the white paper.
3 Rub the balloon 10 times with the wool.
4 Hold the ruler upright with the 0 end against the paper.
Hold the balloon about 10 cm over the paper.
5 Slowly lower the balloon until you see or hear the pepper
being attracted to the balloon.
6 How many millimeters above the paper is the balloon?
Record the distance in the table.
7 Repeat Steps 3–6 for the other four materials. Be sure to rub
the balloon 10 times with each material.
Distance from Paper (mm)
1. Wool
Measurements will vary
depending upon items used.
2.
3.
4.
5.
Conclusion: Which material gave the most charge to the
balloon?
Copyright ©Houghton Mifflin Company. All Rights Reserved.
Material
Answers will vary
18 • ELECTRICITY • SECTION 1 STATIC ELECTRICITY
Student Resource Page 1.5 (p. 18)
Name
Date
STUDENT RESOURCE PAGE 1.6
ACTIVITY SHEET
Graphing Static Charge
Use data from your Measuring Static Charge Resource Page to
make your bar graph.
1 Begin your graph by adding the missing numbers to the
scale at the left.
2 List the materials you tested on the lines across the bottom.
Wool has been done for you.
3 Use your data to decide how tall to make the Wool bar.
Draw a line across the column to mark this height. Shade the
column up to the line.
A The experiment setup
4 Repeat Step 3 for the other materials you tested.
50 mm
45 mm
40 mm
35 mm
Copyright ©Houghton Mifflin Company. All Rights Reserved.
30 mm
25 mm
20 mm
15 mm
10 mm
5 mm
0 mm
Wool
Responses will vary depending on materials selected.
Check graph for logic and accuracy.
ELECTRICITY • SECTION 1 STATIC ELECTRICITY • 19
Student Resource Page 1.6 (p. 19)
10 • EXPERIENCE SCIENCE
4.Students carry out the experiment.
Have students do the experiment. When they finish,
ask: Did all the objects tested have the same effect
on the balloon? How do you know? (No. The pepper
did not react to the balloon in the same way after the
balloon was rubbed by each object.) Which object
tested produced the strongest charge on the
balloon? How do you know? (Responses will vary
depending on objects tested. The object that caused
the balloon to lift the pepper the highest produced the
strongest charge on the balloon.)