Bobby hangs two inflated balloons from 2-meter strings so that they touch. He then holds the balloons apart and rubs each balloon 5 times with animal fur. He then releases the balloons. The balloons now hang a small distance apart from one another:

Question

The next step in Bobby's procedure is to touch the balloons with a metal rod and allow them to settle, and then to rub them 10 times with animal fur. Which result should he expect, and why?

The balloons will hang at the same elevation, because electrical repulsion is an unvarying phenomenon which results from the existence of charge and not its quantity.
The balloons will hang at a greater elevation, because they will have greater charges so the force of electrical repulsion between them will be greater.
The balloons will hang at a smaller elevation, because more thoroughly rubbing them will more completely remove their charges, reducing the electrical repulsion between them.
The balloons will hang straight down or more closely together, because a larger number of rubs with fur will give them opposite rather than like electrical charges.

Answer 1

To understand the expected outcome when Bobby rubs the balloons again with animal fur after touching them with a metal rod, let's analyze each step:

1. Initial Rubbing: When Bobby first rubs the balloons with animal fur, he is charging them. Due to the nature of the materials involved, the balloons acquire like charges (either both positive or both negative), causing them to repel each other. This repulsion is what caused the balloons to hang a small distance apart when they were released.

2. Touching with a Metal Rod: When Bobby touches the balloons with a metal rod, the rod acts as a conductor. If he touches both balloons simultaneously, electrons can flow between the balloons and the rod, potentially neutralizing some of the charges or redistributing them. The exact effect depends on whether the balloons have the same or opposite charge, but typically, touching a conductive object allows for charge equalization.

3. Second Rubbing: After the balloons have had their charges influenced by the metal rod, rubbing them again with animal fur is likely to charge them again. However, because they have already been neutralized to some extent, it is possible they won't charge as strongly.

Given the explanation of how electrical charges work and the effects of rubbing and conduction, the best expectation after conducting this experiment would align with:

• The balloons will hang at a greater elevation, because they will have greater charges, so the force of electrical repulsion between them will be greater.

This is because even after the initial contact with the metal rod, rubbing with fur again is expected to recharge them, potentially resulting in even stronger identical charges if the process of charging with fur is effective. Thus, the balloons will repel each other more forcefully than before, leading them to hang further apart.

In summary, the most accurate reasoning aligns with the idea that repeated charging could lead to an increase in the electrical charge, thus enhancing the repulsive force between the two balloons.