📚 Pressure in a Balloon Mark Scheme | 气球内压力评分标准解析
Understanding how pressure works inside a balloon is a core KS3 CIE physics topic. Mark schemes reward precise use of the particle model, including collisions, force, and pressure, rather than just saying 'the balloon gets bigger'. This revision guide breaks down the key marking points, model answers, and common errors so you can pick up full marks.
理解气球内部的压力如何产生是 KS3 CIE 物理的核心主题。评分标准要求准确使用粒子模型，包括碰撞、力和压强，而不是简单地说 '气球变大了'。本复习指南拆解了关键评分点、标准答案和常见错误，帮助你拿到满分。
1. Understanding the Exam Question | 理解考题要求
Typical questions ask you to explain why a balloon inflates, why it feels firm, or what happens when it is heated or squeezed. The command word 'explain' means you must give a scientific reason using particles, not just describe an observation.
典型的考题会要求你解释为什么气球会膨胀、为什么摸起来很硬，或者气球受热或被挤压时会发生什么。指令词 '解释' 意味着你必须用粒子给出科学原因，而不仅仅是描述现象。
CIE mark schemes for KS3 usually allocate one mark for stating the correct idea and further marks for linking ideas such as collision, force, area, and pressure. Always read how many marks are available and match the number of linked points.
CIE KS3 评分标准通常为正确表述概念给一分，再为串联碰撞、力、面积和压强等观点给更多分。一定要看清题目分值，并匹配相应数量的关联要点。
2. Key Ideas: Particle Model | 核心概念：粒子模型
All matter is made of tiny particles. In a gas, particles are far apart, move randomly at high speed, and collide with each other and with the walls of their container.
所有物质都由微小粒子组成。在气体中，粒子相距很远，高速随机运动，并相互碰撞以及与容器壁碰撞。
The particles inside a balloon are mainly nitrogen and oxygen molecules from the air. They move in straight lines until they hit something, then change direction. This constant bombardment is the microscopic cause of gas pressure.
气球内部的粒子主要是来自空气中的氮分子和氧分子。它们沿直线运动，直到撞到物体才改变方向。这种持续的撞击是气体压强的微观原因。
For KS3, you do not need to name specific molecules, but you should use the word 'particles' or 'gas particles' consistently. Saying 'air pushes' without mentioning particles often loses a mark.
在 KS3 阶段，你不需要说出具体分子名称，但应始终使用 '粒子' 或 '气体粒子' 一词。只说 '空气推' 而没有提到粒子通常会丢分。
3. Pressure from Particle Collisions | 粒子碰撞产生压力
Pressure is caused by gas particles hitting a surface. Each collision exerts a tiny force on that surface. Pressure is the total force exerted per unit area:
压强是由气体粒子撞击表面产生的。每次碰撞都会对表面施加一个微小的力。压强是单位面积上施加的总力：
Pressure = Force ÷ Area
In a balloon, the inner wall is the surface. Millions of particles collide with every square centimetre of the inner wall every second. The total effect of these collisions is the pressure felt by the balloon material.
在气球中，内壁就是受力表面。每秒钟有数百万个粒子撞击内壁的每一平方厘米。这些碰撞的总体效果就是气球材料感受到的压强。
o see N/cm² or N/m². A balloon feels firm because the internal pressure is greater than the pressure caused by the balloon's own elastic squeeze plus external air pressure.
压强的单位是帕斯卡（Pa），1 Pa = 1 N/m²。在 KS3 中你可能还会看到 N/cm² 或 N/m²。气球摸起来很硬，是因为内部压强大于气球自身弹性收缩加上外部空气压强所产生的效果。
4. Why a Balloon Stretches When Inflated | 气球充气时为何膨胀
When you blow air into a balloon, you add more gas particles into a fixed space. The number of collisions with the inner wall increases, so the force on the wall increases, so the pressure inside rises.
当你向气球吹气时，你在固定空间内加入了更多气体粒子。粒子撞击内壁的次数增加，因此作用于壁上的力增大，内部
Published by TutorHao | KS3 Revision Series | aleveler.com
更多咨询请联系16621398022（同微信）
或截图后用「扫一扫 → 相册」选择本图