Pith Ball Lab Directions: Follow the instructions to go through the simulation. Respond to the questions and prompts in the orange boxes. Vocabulary: Coulomb’s law, electrostatic force, gravitational force, induced charge, pith ball, Pythagorean Theorem, tension, vector Prior Knowledge Questions ...
Student Exploration: Pith Ball Lab
Directions: Follow the instructions to go through the simulation. Respond to the questions and
prompts in the orange boxes.
Prior Knowledge Questions (Do these BEFORE using the Gizmo.)
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?
Because of static electricity
2. Why do you think the individual strands of hair are spread apart?
The strands probably all have the same charge so they repel one another
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
, Get the Gizmo ready:
Activity A:
2 to 0.0 × 10-6 C.
● Set q1 and q
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
izmo does not show induced charge. An induced charge occurs
*Note: For simplicity, the Pith Ball Lab G
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?
As the charges get further apart, the distance decreases and the electrostatic force increases
(and vice versa).
3. Observe: Set q1 to -5.0 × 10-6 C. Gradually decrease q2 below 0.0 × 10-6 C.
A. What do you observe? they slowly get further apart
B. What does this tell you about the force the repulsive force is increasing as the charges get
between the pith balls? closer
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?
The distance decreases as I increase q2 . This shows that since q1 is negative and q2 is
an increasing positive number, the electrostatic force increases as well. The
electrostatic force increases as the charges get further apart.
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