A pressure cooker is a pot whose lid can be tightly sealed to prevent gas from entering or escaping. even without knowing how big the pressure cooker is, or what altitude it is being used at, we can make predictions about how much force the lid will experience under different conditions.

Even without knowing the size of the pressure cooker or the altitude at which the pressure cooker will be used, we can easily determine the force on the lid by experience because just as boiling water, the amount of pressure inside the vessel (in this case, the cooker) increases as the temperature increases.