有關摩擦力的圖形

0-1秒: F1(t)=0-0.1kg=0.1t 1-2秒: F2(t)=0.1-0.4kg=0.3t-0.22-3秒: F3(t)=0.7-0.2kg=1.7-t/23-4秒: F4(t)=0.2-0.2kg=0.24秒~: F5(t)=0W=1kg的物體停放在有摩擦力的平面上 如此物體和桌面間靜摩擦係數us=0.5 動摩擦係數為um=0.2 用F=一水平力推此物 問:最大靜摩擦力: Fs.max=0.5*1kg=0.5(kg)動摩擦力: Fm=0.2*1=0.2(kg)物體質量: m=1kgm1.t1=0.5秒時摩擦力為何?F1(0.5)=0.1*0.5=0.05(kg)單獨分析受力情形: Fs=F1=0.05(kg)........ans2.t2=2秒時的摩擦力為何?F2(2)=Fs=0.4(kg)F3(2)=1.7-1=0.7(kg)>Fs.max 物體開始移動: Fm=0.2(kg)..........ans3.t3=3.5秒時的摩擦力為何單獨分析受力情形: F4(t)=Fm=0.2(kg).....ans4.受力物體在t=4.5秒的瞬時加速度為何?單獨分析受力情形求取a=?: F3(t)-Fm=m*a3(t)a3(t)=1.7-t/2-0.2=1.5-t/2=dV3(t)/dtV3(t)=1.5t-t^2/4V3(3)=4.5-9/4=2.25(mps)F4=Fm => V4=V3=2.25(mps)4.5-4=0.5(sec) => s=2.25*0.5=1.125(m)動能=摩擦能: 1*(V4^2-V5^2)/2g=0.2*1.125.......b運動公式: V4^2=V5^2+2*a*sa=(V4^2-V5^2)/(2*1.125)=0.2*g......參考b=1.96(mps^2)..........ans

Maximum static friction (最大靜摩擦力) = 0.5 x 1 kgf = 0.5 kgf
Kinetic friction (動摩擦力) = 0.2 x 1 kgf = 0.2 kgf

1. Friction = 0.1/2 kgf = 0.05 kgf
since the pulling force is still lower than the maximum static friction

2. 0.5 kgf
since the pulling force reaches the maxium static friction

3. 0.2 kgf
the pulling force equals to the kinetic friction.

4. Zero.
The pulling force equals to the kinetic friction => no net force => no acceleration