In der Achterbahn muss man manchmal schreien.

In a rollercoaster, you sometimes need to scream.

[edit: insufficient vocabulary incident] see, there's a problem. Although German tends to be more precise at times, English doesn't really provide a sufficient translation for a more general word like "schreien". "To shout" doesn't exactly cover it and "to cry" doesn't fit that well, either. basically, it's about a mixture of both.

shout and cry.