Bomb calorimeters vs polystyrene cup calorimeters

[Letizia Ye 4F]

During lecture we mentioned bomb calorimeters and normal calorimeters, what is the difference between the two? What conditions and equations apply to each of them?

[mbaker4E]

A bomb calorimeter measures heat flow at a constant volume, as you can imagine a bomb as a rigid chamber that cannot increase in volume. A polystyrene cup calorimeter on the other hand measured changes in temperature at a constant pressure.

[Hedi Zappacosta 1E]

The polystyrene calorimeter is an open system. heat can leave. But a bomb calorimeter is closed and isolated

[Aria Soeprono 2F]

Wouldn't a regular polystyrene calorimeter be an approximation of a closed system, because heat can go out but volume remains the same?