A metal sphere is suspended from a nylon thread. Initially, the metal sphere is uncharged. When a positively charged glass rod is brought close to the metal sphere, the sphere is drawn towards the rod. But if the sphere touches the rod, it suddenly flies away from the rod. Explain, why the sphere is first attracted then repelled?

Explanation

### Step-by-Step Solution:

1. **Understanding the Initial Condition**:
- We start with a metal sphere that is uncharged, meaning it has an equal number of positive and negative charges.

2. **Bringing the Charged Rod Close**:
- When a positively charged glass rod is brought near the uncharged metal sphere, the electric field created by the positive charge of the rod affects the charges in the sphere.

3. **Induction of Charges**:
- The positive charge of the glass rod attracts the electrons in the metal sphere. As a result, the side of the sphere closest to the rod becomes negatively charged (due to the accumulation of electrons), while the side farthest from the rod becomes positively charged (due to the deficiency of electrons).

4. **Electrostatic Attraction**:
- The negatively charged side of the sphere is attracted to the positively charged glass rod. This results in the sphere being drawn towards the rod.

5. **Touching the Rod**:
- When the metal sphere touches the positively charged glass rod, some of the positive charge from the rod is transferred to the sphere. This happens because metals are good conductors of electricity, allowing charge to flow.

6. **Resulting Charge on the Sphere**:
- After touching the rod, the metal sphere becomes positively charged because it has gained positive charges from the rod.

7. **Electrostatic Repulsion**:
- Now that the sphere has a positive charge, it experiences a repulsive force when in the vicinity of the positively charged glass rod. Since like charges repel, the sphere flies away from the rod.

### Conclusion:
- The sphere is first attracted to the rod due to the induction of negative charges on the side closest to the rod. Once it touches the rod, it gains positive charges and is then repelled.