合力
Resultant Forces
把力描述为同时具有大小和方向的矢量，区分平衡力（合力为零，运动状态不变）和非平衡力（合力不为零，导致加速或减速）。
Describe forces as vector quantities with both magnitude and direction, distinguish between balanced forces (zero resultant, no change in motion) and unbalanced forces (non-zero resultant, causes acceleration or deceleration)
学习证据 / Evidence
- 解释什么是矢量，以及为什么力是矢量。
- 计算两个力沿相同或相反方向作用在同一物体上时的合力。
- 解释当力平衡与不平衡时，物体的运动状态分别会发生什么变化。
- 画出静止物体（如放在桌子上的书）的受力图，标出所有力。
- Explains what a vector quantity is and why force is a vector
- Calculates the resultant force when two forces act in the same or opposite directions on an object
- Explains what happens to an object's motion when forces are balanced vs unbalanced
- Draws free body diagrams showing all forces on a stationary object (e.g. a book on a table)
评估问题 / Assessment
如果{{name}}正在推一个放在地板上的重箱子，但箱子没有动，{{name}}能否解释箱子受到的所有力，以及为什么虽然{{name}}在推，箱子却仍然保持静止？
If {{name}} was pushing a heavy box along the floor but it wasn't moving, could they explain all the forces acting on it and why it stays still even though you're pushing?