science-simulations: command not found

Maybe Your $PATH variable doesn't contain the default paths? echo $PATH should give something like:

[root@server ~]# echo $PATH
/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/root/bin

If it's empty, You may set the PATH variable with this command

export PATH="/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/root/bin"

On Debian possible default full paths are:

/usr/bin/science-simulations - from package: science-simulations

You may install the required package with command apt-get install {package}

Error in other languages:
science-simulations: bevel nie gevind nie
science-simulations: comandă negăsită
science-simulations: comando não encontrado
science-simulations: commande introuvable
science-simulations: command not found
science-simulations: käsku ei ole
science-simulations: không tìm thấy lệnh
science-simulations: komanda nerasta
science-simulations: Kommando nicht gefunden.
science-simulations: kommandot finns inte
science-simulations: komut yok
science-simulations: nie znaleziono polecenia
science-simulations: níor aimsíodh an t-ordú
science-simulations: no se encontró la orden
science-simulations: no s'ha trobat l'ordre
science-simulations: opdracht niet gevonden
science-simulations: parancs nem található
science-simulations: perintah tidak ditemukan
science-simulations: príkaz nenájdený
science-simulations: příkaz nenalezen
science-simulations: команда не найдена
science-simulations: командата не е открита
science-simulations: 命令找不到
science-simulations: コマンドが見つかりません