📚 Edexcel A-Level Physics Mechanics (2.1) Combined Revision | 爱德思A-Level物理 力学(2.1) 综合复习
This combined revision guide covers all key concepts in Edexcel A-Level Physics Topic 2.1 – Mechanics: Motion. You will master scalars and vectors, displacement, velocity, acceleration, motion graphs, the SUVAT equations, free fall and projectile motion. Every section pairs clear English explanations with parallel Chinese translations, helping you build deep understanding and exam confidence.
本综合复习指南涵盖爱德思A-Level物理主题2.1——力学：运动的所有核心概念。你将掌握标量与矢量、位移、速度、加速度、运动图像、SUVAT方程、自由落体以及抛体运动。每个部分都以清晰的英文解释与对应的中文翻译配对，助你建立深刻理解与应考信心。
1. Scalars and Vectors | 标量与矢量
A scalar quantity has only magnitude (size), such as distance, speed, mass and time. A vector quantity has both magnitude and direction; examples include displacement, velocity, acceleration and force. Vectors are often represented by arrows, where the length shows magnitude and the arrowhead indicates direction.
标量仅有大小（量值），例如距离、速率、质量和时间。矢量既有大小又有方向；例子包括位移、速度、加速度和力。矢量通常用箭头表示，箭头长度表示大小，箭头指向表示方向。
When adding vectors, you must consider direction. For parallel vectors, simple addition or subtraction applies; for perpendicular vectors, use Pythagoras’ theorem and trigonometry to find the resultant. Resolving a vector into perpendicular components is an essential skill in mechanics.
当进行矢量加法时，必须考虑方向。对于平行矢量，可直接相加或相减；对于互相垂直的矢量，使用勾股定理和三角函数求合矢量。将矢量分解为相互垂直的分量是力学中的基本技能。
R = √F₁² + F₂² θ = tan⁻¹(F₂ / F₁)
2. Distance and Displacement | 距离与位移
Distance is a scalar that measures the total length of the path travelled. Displacement is a vector that measures the straight‑line change in position from the starting point to the finishing point, together with the direction.
距离是标量，衡量运动路径的总长度。位移是矢量，衡量从起点到终点的直线位置变化，并包含方向。
If you walk 3 m east then 4 m north, your distance is 7 m, but your displacement is 5 m at an angle of 53° north of east. In one‑dimensional motion along a straight line, displacement can be positive or negative to indicate direction.
如果你向东走3米再向北走4米，距离是7米，但位移大小为5米，方向为东偏北53°。在沿直线的一维运动中，位移可取正值或负值以表示方向。
3. Speed and Velocity | 速率与速度
e speed = total distance ÷ total time. Average velocity = total displacement ÷ total time.
速率是距离的变化率，为标量。速度是位移的变化率，为矢量。平均速率 = 总距离 ÷ 总时间。平均速度 = 总位移 ÷ 总时间。
Instantaneous velocity is the velocity at a specific moment; it can be found from the gradient of a displacement‑time graph. A constant velocity means both constant speed and unchanging direction.
瞬时速度是某一时刻的速度；可由位移‑时间图像的斜率求得。匀速意味着速率恒定且方向不变。
v = Δs / Δt
4. Acceleration | 加速度
Acceleration is the rate of change of velocity, a vector measured in m s⁻². It can be uniform (constant acceleration) or non‑uniform. Deceleration (negative acceleration) means the velocity is decreasing in the direction of motion.
加速度是速度的变化率，为矢量，单位是米每二次方秒（m s⁻²）。加速度可以是均匀的（恒定加速度）或不均匀的。减速（负加速度）表示沿运动方向的速度在减小。
Average acceleration = change in velocity ÷ time taken. On a velocity‑ gradient gives acceleration, and a straight sloping line indicates constant acceleration.
平均加速度 = 速度变化量 ÷ 所用时间。在速度‑时间图像上，斜率表示加速度，一条倾斜的直线表明加速度恒定。
a = (v − u) / t
5. Displacement‑Time Graphs | 位移‑时间图像
A displacement‑time (s‑t) graph plots displacement on the vertical axis and time on the horizontal axis. The gradient of the line equals the velocity. A horizontal line shows zero velocity (stationary), a straight sloping line indicates constant velocity, and a curve shows acceleration.
位移‑时间图像将位移标于纵轴、时间标于横轴。图像斜率等于速度。水平线表示速度为零（静止），倾斜直线表示匀速，曲线表示加速度。
The instantaneous velocity at a point on a curve is found by drawing a tangent and calculating its gradient. The total displacement is simply the final ordinate value.
曲线上某点的瞬时速度通过作切线并计算其斜率求得。总位移就是终点的纵坐标值。
6. Velocity‑Time Graphs | 速度‑时间图像
A velocity‑time (v‑t) graph shows velocity against time. The gradient gives acceleration. The area under the graph between two times equals the displacement during that interval. This is one of the most powerful tools in kinematics.
速度‑时间图像描绘速度随时间的变化。斜率给出加速度。图像在两个时刻之间的面积等于该段时间内的位移。这是运动学中最有力的工具之一。
- Horizontal line → constant velocity (zero acceleration)
- Sloping straight line → constant acceleration
- Curve → varying acceleration
- 水平线 → 匀速（零加速度）
- 倾斜直线 → 匀加速
- 曲线 → 加速度变化
To calculate displacement from a v‑t graph, split the area into simple shapes (rectangles, triangles) and sum them, remembering that areas below the time axis represent negative displacement.
要根据速度‑时间图像计算位移，可将面积拆分为简单形状（矩形、三角形）并求和，注意时间轴下方的面积表示负位移。
7. Equations of Motion (SUVAT) | 运动学方程 (SUVAT)
For motion in a straight line with constant acceleration, there are five key quantities, often remembered with the acronym SUVAT: s (displacement), u (initial velocity), v (final velocity), a (acceleration) and t (time). The four equations link these quantities.
对于匀加速直线运动，有五个关键量，常用首字母缩写SUVAT记忆：s（位移）、u（初速度）、v（末速度）、a（加速度）和t（时间）。四个方程将这些量联系起来。
v = u + a t
s = u t + ½ a t²
s = ½ (u + v) t
v² = u² + 2 a s
Each equation omits one quantity: the first omits s, the second omits v, the third omits a, and the fourth omits t. You must identify which three quantities you know and which you need, then choose the equation that links them.
每个方程都省略了一个量：第一个省去s，第二个省去v，第三个省去a，第四个省去t。你必须确定已知哪三个量以及需要求哪个量，然后选择联系它们的方程。
Always define a positive direction before using SUVAT. Vector quantities like s, u, v and a must be assigned signs accordingly.
在使用SUVAT前务必规定正方向。如s、u、v和a这样的矢量必须相应赋予正负号。
8. Free Fall | 自由落体
an object under the influence of gravity alone, with negligible air resistance. Near Earth' ation, so the SUVAT equations apply with a = g (or −g, depending on your sign convention).
自由落体是仅在重力作用下、空气阻力可忽略的物体运动。在地表附近，所有物体以相同的恒定加速度g = 9.81 m s⁻² 向下运动。这是匀加速的特殊情况，因此可使用SUVAT方程，其中a = g（或 −g，取决于正方向的规定）。
If an object is thrown upward, at its highest point the velocity is momentarily zero but acceleration is still g downwards. The time to reach maximum height equals the time to fall back to the original level, assuming no air resistance.
若物体被向上抛出，在最高点速度瞬时为零，但加速度仍为向下的g。在忽略空气阻力的情况下，上升至最高点的时间与落回原高度的时间相等。
v = u − g t (if upward is positive)
9. Projectile Motion | 抛体运动
rtical components of motion are independent. The horizontal velocity remains constant, while the vertical motion is governed by SUVAT equations with a = ±g.
抛体在恒定重力加速度下运动，水平方向无加速度（忽略空气阻力）。运动的水平分量与竖直分量相互独立。水平速度保持不变，而竖直运动由a = ±g的SUVAT方程支配。
to horizontal and vertical components: uₓ = u cos θ, uᵧ = u sin θ. Use horizontal constant‑ upward as positive). The time of flight is often the key link between the two components.
解抛体问题时，将初速度分解为水平和竖直分量：uₓ = u cos θ, uᵧ = u sin θ。水平方向使用匀速公式sₓ = uₓ t。竖直方向以a = −g（取向上为正）应用SUVAT方程。飞行时间通常是联系两个分量的关键。
Typical exam question: calculating range, maximum height, time of flight, and impact velocity. Remember that at the highest point, vertical velocity is zero; range is horizontal displacement during the total time of flight.
典型的考题：计算射程、最大高度、飞行时间和落地速度。记住在最高点竖直速度为零；射程是整个飞行时间内的水平位移。
10. Determining g Experimentally | 实验测定 g
ields a straight line through the origin with gradient ½ g. A more accurate method uses a trapdoor and electromagnet or light gates with a data‑logger.
通过测量物体从静止下落到已知距离所用的时间，可求出g值。利用s = ½ g t²，绘制s–t²图像可得到一条过原点的直线，其斜率为½ g。更精确的方法使用活板门与电磁铁，或光门配合数据采集器。
Another common approach is the free‑fall apparatus with a metal ball bearing: the time to fall between two light gates is recorded. Rearranging SUVAT allows g to be calculated without needing the initial velocity. Typical systematic errors include reaction time and air resistance.
另一种常见方法是使用金属球轴承的自由落体装置：记录小球通过两光门之间的时间。重新整理SUVAT方程可在不需求初速度的情况下计算g。典型的系统误差包括反应时间和空气阻力。
Published by TutorHao | Physics 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