Ƙarfin da aka saba amfani da shi shine ƙarfin da ke aiki akan abubuwan da ke hulɗa, inda alkiblar ƙarfin take daidai da matakin hulɗa. Alamarsa ita ce N kuma tsarin raka'a na duniya shine kg m/s 2 ko Newton.
Tilasta N a kan saman da aka yi da siminti
N shine ƙarfin da ƙasa ke amfani da shi a kan katako, N' shine ƙarfin da katako ke amfani da shi a ƙasa. w shine ƙarfin nauyi da ke aiki akan katako ko nauyin katako. N da N' sune ƙarfin aiki da martani, yayin da N da w ba ƙarfin aiki da martani ba ne.
Idan toshen yana hutawa ko kuma ba ya motsi a tsaye, ana iya ƙididdige girman ƙarfin N ta amfani da dokar farko ta Newton.
ΣF y = 0
N – w = 0
N = w
Idan aka tura tubalan ƙasa da ƙarfi F kamar yadda yake a hoton da ke gefe, to girman ƙarfin N shine:
ΣF y = 0
N – w – F = 0
N = w + F
Ƙarfin da aka saba da shi a kan jirgin sama mai karkata
N da N' su ne ƙarfin aiki da amsawa. N shine ƙarfin yau da kullun da ke aiki akan toshe kuma N' shine ƙarfin yau da kullun da ke aiki akan matakin karkata. W shine ɓangaren tsaye na ƙarfin nauyi (w). Ƙarfin nauyi (w) yana aiki akan toshe. Girman ƙarfin yau da kullun shine
ΣF y = 0
N – w y = 0
N = w y = w cos theta
