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 chine huremu kuti chishanduke muchacha 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 zvose hukuru nerudzivo zvichireva kuti fosi chiyero chemhando yemuchovha. Mutemo wechipiri waNewton, F = ma, pawakatanga kunyorwa wakanga wakati siyanei zvishoma, asi mumashoko akafanana: mutemo wakanyorwa naiye Isaac 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 ine tsazaniso inoti F → i k u r u = m ⋅ a →   {\displaystyle {\vec {F}}_{ikuru}=m\,\cdot {\vec {a}}\ } Fikuru (net) yakamirira fosi inoyerwa mumaNewtons m yakamirira huremu hunoyerwa nema kg a yakamirira rufangu runoyerwa muma(m/s2) Kupangura (force way into) zvichireva kupasura kana kupatsanura.