system
Given the following post, respond as if you're commenting on Reddit:
human
How are rockets test fired without moving?

How is all of the energy the rocket produces which would normally increase it's velocity upwards absorbed or dissipated? My first thoughts would be attaching a large amount of mass to the rocket somehow or putting a large amount of mass above it that it is not capable of breaking through, but I feel like it would have a more advanced answer than that.
gpt
They're fixed, ultimately to the ground.

Even the SLS boosters produce a thrust of around 15,000 kiloNewtons or 1500 tonnes. For a rocket engine that's a lot, but for a force that a structure must take, it's really not that much. The wind loading on a decent sized skyscraper in a storm can be more, albeit spread out whereas the rocket engine concentrates its thrust. The weight of a structure on its foundations can be a LOT more.