Which of the following statements is incorrect?

Options

A. Friction acts on a writing.
B. Friction acts on a boat moving on water.
C. Friction acts on a bicycle moving on a smooth road.
D. Friction does not act on a ball moving through air.

Answer

To determine which statement is incorrect regarding friction, let's analyze each option provided:

### Step 1: Analyze Option 1
**Statement:** Friction acts on writing.
**Analysis:** When writing, the pen (or pencil) and the paper are in contact. Friction between these two surfaces allows the pen to leave a mark on the paper.
**Conclusion:** This statement is **correct**.

### Step 2: Analyze Option 2
**Statement:** Friction acts on a boat moving on water.
**Analysis:** As the boat moves, there is friction between the water and the bottom of the boat. This friction is what allows the boat to move forward.
**Conclusion:** This statement is **correct**.

### Step 3: Analyze Option 3
**Statement:** Friction acts on a bicycle moving on a smooth road.
**Analysis:** For a bicycle to move, there must be friction between the tires and the road. Even on a smooth road, some friction is necessary for the bicycle to accelerate and decelerate.
**Conclusion:** This statement is **correct**.

### Step 4: Analyze Option 4
**Statement:** Friction does not act on a ball moving through air.
**Analysis:** When a ball moves through the air, there is indeed friction between the surface of the ball and the air. This is known as air resistance or drag. Therefore, the statement that friction does not act is incorrect.
**Conclusion:** This statement is **incorrect**.

### Final Answer
The incorrect statement is **Option 4**: "Friction does not act on a ball moving through air."

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