Why does a hot air balloon rise when the air inside it is heated?

Question

BlackTom AI · Accepted Answer

Consider the scenario: a hot air balloon rises because the air inside the balloon is heated and becomes less dense than the surrounding cooler air.
Option 1: 'The number of gas molecules increases.' In a closed balloon, heating does not create more molecules; it increases their average kinetic energy. The count of molecules remains essentially the same, so this explanation misattributes the rise to quantity rather than density changes.
Option 2: 'The temperature increases, causing the air to expand and become less dense.' This is the key physics: heating raises the air's temperature, which causes the gas to expand. Because the balloon's envelope confines the gas, the expanded air has a larger volume but the same amount of mass, leading to lower density. The less-dense inside air provides a buoyant force that lifts the balloon.
Option 3: 'The pressure inside the balloon decreases.' While external pressure is lower at altitude, the pressure inside the balloon does not need to decrease to rise; in fact, heating can raise internal pressure unless the envelope expands. The rise is primarily about density differences, not a simple drop in internal pressure.
Option 4: 'The air inside turns into a liquid.' This is physically incorrect for typical hot-air balloons operated at temperatures well above ambient air; the air remains a gas, not a liquid, so this option misstates the state of matter under normal operating conditions.

Why does a hot air balloon rise when the air inside it is heated? 单项选择题

类似问题

A ping-pong ball has an average density of 0.140 g/cm3 and a diameter of 3.80 cm. What force would be required to keep the ball completely submerged under water?

If an object weighing 50N displaces a volume of water with a weight of 10 N, what is the buoyant force on the object?

An object sinks when it displaces a volume of liquid that has a weight

A glass of ice water is filled to the brim with water; the ice cubes stick up above the water surface. After the ice melts, which is true?

What are the ways to create buoyancy in seawater? Pick 2

A block of wood with dimensions of length = 1.6m, width = 0.4m and height = 1m, is placed in water, what is the buoyant force? The density of water is 1000kg/m3. Answer to 1 decimal places and only put in the numerical value. Do not write the unit in your answer.

A parcel of air is buoyant when:

更多留学生实用工具

智能学习助手

风格化写作助手

论文查重助手

文献引用助手

课堂转译助手

课堂笔记助手

Quiz搜索助手

学校历年真题

智能刷题助手

智能匹配练习

希望你的学习变得更简单