How to use this tool
Drag the orange load or use the sliders. Choose A or B and compare the moment arms. Notice that the reaction through the chosen point contributes no moment. In Exam Practice, choose a point, select a moments equation, and calculate your answer. Use Show hint if you get stuck.
中文辅助：术语与解题步骤
- Moment
- ：力矩
- Moment arm
- ：力臂，即取矩点到力的作用线的垂直距离
- Support reaction
- ：支承反力
- Uniform beam
- ：均匀梁，重力作用在中点
- Clockwise / anticlockwise
- ：顺时针／逆时针
- Equilibrium
- ：平衡，合力和合力矩都为零
- 选 A 或 B 取矩。通过该点的反力力臂为零，可从力矩方程中消去。
- 用「力 × 垂直力臂」算每个力的力矩。平衡时，顺时针力矩总量等于逆时针力矩总量。
- 求出一个支承反力后，用「向上力之和＝向下力之和」求另一个。若题目求载荷位置，记得从 B 取矩时载荷力臂是 6 − x，答案 x 仍从 A 量起。
Beam force diagram
Take moments about
Move the load and compare reactions
The beam is 6 m long and its weight acts at the midpoint. Move the load towards either support and watch that support’s reaction increase.
中文题意
Anticlockwise moments are positive. The moment arm is the perpendicular distance from the chosen point to the force’s line of action.
| Force | Moment arm | Direction | Moment (N·m) |
|---|
Working with an angled force? Practise in Moments & Angles Lab.