Question

Occasionally, people who gain static charge by shuffling their feet on the carpet will have their hair stand on end. Why does this happen?

Short answer

Answer: A person's hair stands on end when they gain static charge by shuffling their feet on the carpet because the excess electrons in their body make them negatively charged, causing repulsion between their hair strands. When the repulsive force becomes greater than the force of gravity, the hair will stand on end. Once the static charge is discharged and the repulsive force reduces, gravity will dominate again, causing the hair to fall back to its normal position.

Step-by-step solution

Understand static electricity

When a person shuffles their feet on the carpet, they build up an excess of static charge, which is an imbalance of electrical charges within or on the surface of an object. In this case, the person's body gains excess electrons, which makes it negatively charged. These excess electrons create a negatively charged person, which would cause the hair to stand on end.

Force between charged objects

Like charges repel each other, while opposite charges attract. In our scenario, the hair strands are also negatively charged due to the excess electrons in the person's body. So, the force between the charged objects causes repulsion, which leads to the hair strands repelling each other.

Balancing the forces

When the repulsive force between the charged hair strands becomes greater than the force of gravity acting on the strands, the hair will stand on end. This means that once the person's body has a strong enough negative charge, the repulsion between the hair strands will overcome gravity and cause the hair to stand on end.

Hair falling back down

Once the static charge is discharged, the repulsive force between hair strands would reduce. This will result in the force of gravity eventually becoming dominant again, causing the hair to fall back to its normal position.