A space-ship entering the earths atmosphere is likely to catch fire, this is due to

Options

A. surface tension of air
B. viscosity of air
C. greater proportional of `O_2` in the atmosphere at higher height
D. high temperature of upper atmosphere

Answer

To solve the question about why a spaceship entering the Earth's atmosphere is likely to catch fire, we can break down the reasoning step by step:

### Step 1: Understanding the Environment
When a spaceship re-enters the Earth's atmosphere, it is not in a vacuum. Instead, it is surrounded by air molecules. This is crucial because the presence of air affects the spaceship's descent.

**Hint:** Consider the role of air molecules in the atmosphere when an object moves through it.

### Step 2: Speed of the Spaceship
As the spaceship descends, it travels at a very high speed. This high velocity is significant because it increases the interaction between the spaceship and the air.

**Hint:** Think about what happens to an object moving quickly through a medium like air.

### Step 3: Air Resistance
As the spaceship moves through the atmosphere, it encounters air resistance, also known as drag. This resistance opposes the motion of the spaceship and generates friction between the air particles and the surface of the spaceship.

**Hint:** Reflect on the concept of friction and how it is generated when two surfaces interact.

### Step 4: Generation of Heat
The friction caused by air resistance leads to an increase in temperature. The faster the spaceship moves, the greater the friction and, consequently, the higher the temperature generated.

**Hint:** Consider how friction affects temperature in everyday situations, like rubbing your hands together.

### Step 5: Ignition and Fire
If the temperature of the spaceship's surface rises sufficiently due to this friction, it can lead to combustion, resulting in the spaceship catching fire. This is a critical factor during re-entry.

**Hint:** Think about the conditions required for fire to occur and how temperature plays a role.

### Conclusion
The reason a spaceship is likely to catch fire upon entering the Earth's atmosphere is primarily due to the viscosity of air, which contributes to the friction and heat generated during its high-speed descent.

**Final Answer:** The correct option is **viscosity of air** (Option 2).