Which one is a contact force?

Options

A. Electrostatic force
B. Magnetic force
C. Frictional force
D. Gravitational force

Explanation

To determine which of the given forces is a contact force, we can analyze each option step by step:

### Step 1: Understand the Definition of Contact Force
A contact force is a force that acts at the point of contact between two objects. It requires physical contact between the objects to exert the force.

### Step 2: Analyze Each Force
- **Electrostatic Force**: This is a force that acts between charged objects. It does not require contact; it can act over a distance.

- **Frictional Force**: This force occurs when two surfaces are in contact with each other. It opposes the relative motion of the surfaces. For example, when you slide an object across a table, friction acts at the point of contact.

- **Magnetic Force**: Similar to electrostatic force, magnetic force can act over a distance between magnets or magnetic materials without direct contact.

- **Gravitational Force**: This force acts between two masses and does not require contact. It acts at a distance, such as the force that pulls objects towards the Earth.

### Step 3: Identify the Contact Force
From the analysis, we see that the only force that requires direct contact between objects is the **frictional force**.

### Conclusion
Thus, the answer to the question is that the **frictional force** is the contact force among the options provided.

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