NapkinCalc

Physics 1 — Motion & Energy

Newton’s second law & friction

continues from lesson 3 — values defined earlier in the course stay live here

F = m·a, but the F is the NET force. Push a box and friction pushes back with f = μ·N, where N is how hard the surfaces press together — on level ground, just the weight. Draw the forces first, then add them up:

free-body diagram of the box — the four forces computed below
free-body diagram of the box — the four forces computed below
mbox:=10kgm_{box} := 10 kg = 10 kg
Fpush:=50NF_{push} := 50 N = 50 N applied force
μk=0.4\mu_{k} = 0.4 kinetic friction coefficient
Nf:=mbox∗gN_{f} := m_{box} * g = 98.1 N normal force
fk=μk⋅Nff_{k} = \mu_{k} \cdot N_{f} = 39.24 N friction force
anet=Fpush−fkmboxa_{net} = \frac{F_{push} - f_{k}}{m_{box}} = 1.076 N / kg net acceleration
✓ pass Fpush>fkF_{push} > f_{k} does it move at all? push harder than friction