Pith Ball Lab Answer Key
Vocabulary: Coulomb’s law, electrostatic force, gravitational force, induced charge, pith ball,
Pythagorean Theorem, tension, vector
Prior Knowledge Questions (Do these BEFORE using the Gizmo.)
[Note: The purpose of these questions is to activate prior knowledge and get students thinking.
Students are not expected to know the answers to the Prior Knowledge Questions.]
1. A girl rubs a balloon on her head and then holds it a short
distance away. Why does her hair stick to the balloon?
Sample answer: Electrons move from the hair to the balloon,
giving the balloon a negative charge and the hair a positive
charge. The positive hair is attracted to the negative balloon.
2. Why do you think the individual strands of hair are spread apart?
The positive strands of hair are repelled from each other.
Gizmo Warm-up
The girl’s hair was attracted to the balloon by the electrostatic
force, a force between all charged objects. Most objects acquire a
charge (q) by gaining or losing electrons. Objects that gain
electrons become negatively charged, while objects that lose
electrons become positively charged.
The Pith Ball Lab Gizmo™ shows two pith balls hanging by
strings. Pith balls are made from lightweight material that can
easily acquire a charge. To begin, check that the charge on each
pith ball (q1 and q2) is 0.0 × 10-6 coulombs (C).
Use the sliders to test each combination of charges listed below. State whether the electrostatic
force is attractive (balls move together), repulsive (balls move apart), or zero (balls don’t move).
Charge on left ball (q1) Charge on right ball (q2) Electrostatic force
Positive Zero Zero
Zero Negative Zero
Positive Positive Repulsive
Negative Negative Repulsive
Positive Negative Attractive
This study source was downloaded by 100000808701186 from CourseHero.com on 02-26-2022 00:44:46 GMT -06:00
https://www.coursehero.com/file/56061959/Pith-Ball-Lab-Answer-Key-Vocabularydoc/
, Get the Gizmo ready:
Activity A:
Set q1 and q2 to 0.0 × 10-6 C.
Coulomb’s law Set the mass of the pith balls to 5 grams.
Check that g is 9.8 m/s2 and L is 0.50 m.
Question: What factors affect the force between charged objects?
1. Summarize: Summarize what you have learned so far by filling in the blanks:
If the two charges are the same, the force is repulsive.
If the two charges are opposite, the force is attractive.
If one of the charges is zero, the force is zero.*
*Note: For simplicity, the Pith Ball Lab Gizmo does not show induced charge. An induced
charge occurs when a charged object is brought near a neutral object, causing the electrons
in the neutral object to move away from or towards the charged object. This results in an
attractive force between the charged object and the neutral object.
2. Predict: How do you think the strength of electrostatic force is related to the charges on the
balls and the distance between them? Predictions will vary.
3. Observe: Set q1 to -5.0 × 10-6 C. Gradually decrease q2 below 0.0 × 10-6 C.
A. What do you observe?
As q2 decreases, the pith balls are repelled farther and farther apart.
B. What does this tell you about the force between the pith balls?
As q2 decreases, the repulsive force between the pith balls increases.
4. Observe: Now slowly increase q2 above 0.0 × 10-6 C. What do you observe, and what does
this tell you about the electrostatic force?
As q2 increases, the balls move closer and closer together. Above 0.3 × 10-6 C, the pith balls
are pulled very close together. This indicates that the electrostatic force is attractive and
increases as q2 increases.
(Activity A continued on next page)
This study source was downloaded by 100000808701186 from CourseHero.com on 02-26-2022 00:44:46 GMT -06:00
https://www.coursehero.com/file/56061959/Pith-Ball-Lab-Answer-Key-Vocabularydoc/
Vocabulary: Coulomb’s law, electrostatic force, gravitational force, induced charge, pith ball,
Pythagorean Theorem, tension, vector
Prior Knowledge Questions (Do these BEFORE using the Gizmo.)
[Note: The purpose of these questions is to activate prior knowledge and get students thinking.
Students are not expected to know the answers to the Prior Knowledge Questions.]
1. A girl rubs a balloon on her head and then holds it a short
distance away. Why does her hair stick to the balloon?
Sample answer: Electrons move from the hair to the balloon,
giving the balloon a negative charge and the hair a positive
charge. The positive hair is attracted to the negative balloon.
2. Why do you think the individual strands of hair are spread apart?
The positive strands of hair are repelled from each other.
Gizmo Warm-up
The girl’s hair was attracted to the balloon by the electrostatic
force, a force between all charged objects. Most objects acquire a
charge (q) by gaining or losing electrons. Objects that gain
electrons become negatively charged, while objects that lose
electrons become positively charged.
The Pith Ball Lab Gizmo™ shows two pith balls hanging by
strings. Pith balls are made from lightweight material that can
easily acquire a charge. To begin, check that the charge on each
pith ball (q1 and q2) is 0.0 × 10-6 coulombs (C).
Use the sliders to test each combination of charges listed below. State whether the electrostatic
force is attractive (balls move together), repulsive (balls move apart), or zero (balls don’t move).
Charge on left ball (q1) Charge on right ball (q2) Electrostatic force
Positive Zero Zero
Zero Negative Zero
Positive Positive Repulsive
Negative Negative Repulsive
Positive Negative Attractive
This study source was downloaded by 100000808701186 from CourseHero.com on 02-26-2022 00:44:46 GMT -06:00
https://www.coursehero.com/file/56061959/Pith-Ball-Lab-Answer-Key-Vocabularydoc/
, Get the Gizmo ready:
Activity A:
Set q1 and q2 to 0.0 × 10-6 C.
Coulomb’s law Set the mass of the pith balls to 5 grams.
Check that g is 9.8 m/s2 and L is 0.50 m.
Question: What factors affect the force between charged objects?
1. Summarize: Summarize what you have learned so far by filling in the blanks:
If the two charges are the same, the force is repulsive.
If the two charges are opposite, the force is attractive.
If one of the charges is zero, the force is zero.*
*Note: For simplicity, the Pith Ball Lab Gizmo does not show induced charge. An induced
charge occurs when a charged object is brought near a neutral object, causing the electrons
in the neutral object to move away from or towards the charged object. This results in an
attractive force between the charged object and the neutral object.
2. Predict: How do you think the strength of electrostatic force is related to the charges on the
balls and the distance between them? Predictions will vary.
3. Observe: Set q1 to -5.0 × 10-6 C. Gradually decrease q2 below 0.0 × 10-6 C.
A. What do you observe?
As q2 decreases, the pith balls are repelled farther and farther apart.
B. What does this tell you about the force between the pith balls?
As q2 decreases, the repulsive force between the pith balls increases.
4. Observe: Now slowly increase q2 above 0.0 × 10-6 C. What do you observe, and what does
this tell you about the electrostatic force?
As q2 increases, the balls move closer and closer together. Above 0.3 × 10-6 C, the pith balls
are pulled very close together. This indicates that the electrostatic force is attractive and
increases as q2 increases.
(Activity A continued on next page)
This study source was downloaded by 100000808701186 from CourseHero.com on 02-26-2022 00:44:46 GMT -06:00
https://www.coursehero.com/file/56061959/Pith-Ball-Lab-Answer-Key-Vocabularydoc/
