Electrostatic Fields & Forces (Noelle Eagle)

Title: Electrostatic Fields & Forces

Principle(s) Investigated: Electrostatic fields and the forces they exert.

Standards:

MS-PS2-5. Conduct an investigation and evaluate the experimental design to provide evidence that fields exist between objects exerting forces on each other even though the objects are not in contact.

Materials: balloons (2), twine or string, glass rod, hair or wool, 100% silk scarf.

Procedure:

1. Blow up two balloons. Don’t fill them too much, or they will be difficult to handle.

2. Tie one of the balloons to a piece of twine or string and suspend it from the ceiling or other elevated location.

3. Rub the balloons on your hair or a piece of wool.

4. Pick up a balloon and bring it close to the suspended balloon to demonstrate how they repel each other.

5. Next, take the glass rod and rub it with the silk scarf or piece of silk cloth.

6. Put the glass rod near the suspended balloon to demonstrate the attraction between them.

Student prior knowledge: Before learning about electrostatics, students should know the definition of a force (a push or a pull), and they should be familiar with the subatomic particles of atoms and their charges (positively charged protons, neutral neutrons, and negatively charged electrons). Students should also have learned about the force of gravity that attracts matter.

Explanation: The electrostatic fields of the balloons become negatively charged when you rub them on your hair (or a piece of wool), because they collect extra electrons for your hair (or the wool).The electrostatic fields of the balloons push away from each other because they are both negatively charged and like charges repel. The balloons push each other without their surfaces touching because their electrostatic fields are exerting a repellent electrostatic force. When the glass rod is rubbed on the silk scarf or cloth, the rod loses electrons and becomes positively charged. When the glass rod now has a positive electrostatic field and the balloon has a negative electrostatic field, they will move towards each other because unlike charges have an attractive electrostatic force.

Questions & Answers:

1. Why don’t the balloons and glass rod stay charged and maintain their repelling and attracting effects?

Answer: Objects do not stay charged because the electrons dissipate and the objects go back to having a neutral charge. Protons in the vicinity attract the electrons and remove them from the balloon. The glass rod, which is positively charged, attracts electrons and becomes neutral again.

2. How do we know that there are two types of electrostatic charge?

Answer: We can see that there are two types of charges (positive and negative) because of the different forces observed when two charged balloons are brought near each other versus the balloon and the glass rod. When the negatively charged balloons repel each other, that is evidence of their two like charges interacting. The attraction between the negatively charged balloon and the positively charged glass rod shows us that two unlike charges are interacting.

3. Why does the glass rod need to be close to the balloon in order to attract it?

4. Answer: The strength of the electrostatic force decreases as objects move farther away from each other because of the inverse square law. For example, when the distance from the source of the electrostatic field is doubled, the intensity of the electrostatic force will be one fourth of its original intensity.

Applications to Everyday Life:

1. Static cling occurs when laundry is tumbling in the dryer, because the clothing is rubbing together, which allows electrons to move from one item to another. For example, a sock may remove electrons from a sweater, so that the net charge of the sock is negative and the net charge of the sweater is positive. Their unlike net charges cause them to attract each other and stick together.

2. Coming your hair with a plastic comb allows electrons to be removed from your hair and build up on the comb. Your comb will have a negative net charge and your hair will have a positive net charge. The positive charge on the individual strands of hair will cause them to push away from each other, because like charges repel each other.

3. Lightning is a dramatic example of electrostatics. Lightning moisture in the air becomes electrically charged as either positive or negative net charges. The smaller droplets become positively charged and the larger ones become negatively charged. Air currents separate the water droplets so that the positively charged ones are in the upper section of the cloud and the negatively charged droplets move to the lower area of the cloud. As the strength of the charges increase, the air is ionized, so that it can no longer act as an insulator between the positive and negative charges that are separated in the cloud. This lack of insulation allows the lightning bolt to jump and we see its energy in the form of a bright flash of light.

Photographs:

Videos:

Electrostatic Fields & Forces Demo 🎈 https://www.youtube.com/watch?v=O0FYWbK6p1U