概念
A1 kinematics
scalar and vector
position, displacement, distance
uniform motion: position changes by the same amount per unit time
velocity, average speed
acceleration
graphs of motion (\(a(t)=\frac{dv}{dt}\), while \(v(t)=\frac{dd}{dt}\))
projectile motion (component independent)
A2 force
Force, weight, tension, Hooke’s law, normal contact force(支持力), drag force, buoyant force, friction (dynamic and static),
| friction | |
|---|---|
| ![[_resources/Pasted image 20260228111038.png]] | dynamic friction vs static friction |
free-body force diagram
equilibrium, resultant/net force
==Newton First Law==: when net force is zero, the object moves in constant velocity (can be zero), also the law of ==inertia== ==Newton Second Law==: F=ma ==Newton 3rd Law==: If body X exerts a force on body Y, Y exerts a force with same magnitude but opposite direction to X.
circular motion requires: a net force directed towards the circle center
period, angular speed, frequency
centripetal acceleration
centripetal force (remember, it is always a resultant force!)
A3 work, energy, power
work done (same direction in displacement as the force direction)
kinetic energy - \(\Delta E_k = \text{work done}\)
gravitational potential energy
elastic potential energy
total mechanical energy (conservation) - conserved only if the system is isolated (no work done from outside system) - conserved if there is no loss to surrounding (air friction, light spring)
power
efficiency
conservation of energy
Sankey Diagram
| ![[_resources/Pasted image 20260228112944.png]] | Sankey Diagram |
A4 momentum
linear momentum - impulse 是动量的改变 - \(F=\frac{dp}{dt}\) -> If there is net force change, momentum must change - impulse/force diagram
==conservation of momentum==: when net force of a system is 0 (and no external force acting on system), momentum is conserved
elastic collision: kinetic energy is conserved inelastic collision: kinetic energy is not conserved total inelastic collision: kinetic energy is totally transferred to other type of energy like heat
常见敌人
inclined plane question (with friction) - 受力分析图 - 做工和能量不要忘记potential energy和重力的做工
centripetal force is resultant force, 合力越大，转的速度也越大
impulse 是动量的改变 算impulse记得带上符号变化 只要给了force vs time的图，impulse是积分面积，不能直接用F=pt算
带方向和角度的拆成x,y component，参考系方向灵活（拉力用拉力方向当参考系）
collision 中momentum不变（用作用力和反作用力变动量证明）
17M-P1-TZ1-SL当结论
用friction判断运动方向
momentum ratio: two objects in one system
calculate kinetic energy ratio from momentum ratio: remember \(E \propto mv^2\), do not forget any terms
计算位移：记得带上初始位移
opposing force: force acting on the direction opposite to the movement
see Force-distance graph, think of the work