What do you understand by frictional force?

Explanation

### Step-by-Step Solution:

1. **Definition of Frictional Force**:
- Frictional force is defined as the force that resists the sliding or rolling of one object over another. It acts when two surfaces are in contact.

2. **Nature of Friction**:
- Friction is a type of contact force. This means that it occurs when two surfaces are physically touching each other.

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