IGCSE物理备考：运动学必考的知识点

IGCSE物理Motion运动

01、Speed 速率

Speed is defined as the distance traveled per unit time.If the speed of something is changing, it is accelerating. The acceleration of free fall near to the Earth is constant.average speed = total distance / total time

划重点：

只要speed发生变化，就说明acceleration加速度不等于零。

02、Distance 路程

Distance is measured in mm, cm, m or km and time measured in ms, s, minutes or hours.Remember to convert units to make sure everything is equivalent! For example if distance is in ���m and time is in ℎou���, then calculate distance/1000 and time× (60 × 60)to get everything in metres and seconds.划重点：

通常在物理的计算中会把各个物理量的单位都换算为base unit（基本单位），distance的基本单位是m（米），时间的基本单位是second（秒）

distance（路程）

03、Velocity 速度

Velocity is the speed in a given direction.划重点：

Velocity和speed不同，speed是一个scalar，只有大小，而velocity是一个vector，既有大小又有方向。

因此一个物体的velocity千万不要忘记考虑方向哦！

04、Acceleration 加速度

Acceleration is the rate of change of velocity:a=(v-u)/t

划重点：

加速度也是一个vector，一个有方向的物理量。

05、Displacement-time graph 位移时间图像

In a displacement-time graph:The gradient is velocityNegative gradient is returning back to the starting point .

A horizontal line means it is stationaryIf the distance is zero, it is back at the starting pointA curved line means that the velocity is changing and it is accelerating.划重点：

位移时间图像斜率是速度。

斜率的正负代表正负方向

06、Velocity-time graph 速度时间图像

In a velocity-time graph:The gradient is accelerationNegative gradient (i.e. negative acceleration) is decelerationIf the speed is zero, it is at restA horizontal line means constant speedThe area under the line is the distance travelledA curved line means that the acceleration is changing.划重点：

速度时间图像的斜率是加速度，斜率的正负代表加速度的方向。