Muchidzidzo chefundoyetsimba,Fosi (Force) kusvudzira kunoita kuti mutumbi ushanduke mukufamba kwauri kuita, murudzivo rwahuri kufamba kana kuti mukuumbwa kwacho. Izvi zvinoreva kuti fosi inokonzeresa chinhu chinehuremu kuti chishandukemuchacha wacho (zvichisanganisa kutanga kufamba kwacho mukubva kumira), i.e.rufangu; kana kuti fosi inokonzeresa mitumbi usina kusimba kuti ushanduke mukuumbwa kwahwo. Fosi inogona kutsanangurwa nenzira dziri nyore dzakadai sekusunda kana kuzvuva. Fosi ine zvosehukuru nerudzivo zvichireva kuti fosi chiyero chemhando yemuchovha.Mutemo wechipiri waNewton,F =ma, pawakatanga kunyorwa wakanga wakati siyanei zvishoma, asi mumashoko akafanana: mutemo wakanyorwa naiyeIsaac Newton unoti fosi ikuru (net force) inoshanda pane mutumbi hwakaenzana nerheti yekushanduka kwerunhanhira (momentum).
Fosi inopimwa nechiyero chinonzi Newton (N). Mutemo wechipiri waNewton unoti fosi inetsazaniso inoti
- Fikuru (net) yakamirira fosi inoyerwa mumaNewtons
- m yakamirirahuremu hunoyerwa nema kg
- a yakamirirarufangu runoyerwa muma(m/s2)
