In the Project Hail Mary book, after Ryland Grace wakes up from his 4 year coma (with temporary amnesia) he notices he feels heavier than he should. He is locked in a room, unable to leave until he remembers his name. During which he comes up with an experiment to determine the gravitational field strength he is experiencing. This part of the book was missing in the film!

​

He knows that the swing of a pendulum doesn't depend on its mass or length, just gravity. So he sets out to measure the period of a pendulum in order to determine how much gravity he is under. He measures the time for many swings to find the average period. He rearranges the equation for the period of a pendulum to find what his value for g is (he finds that he is experiencing 1.5gs).

​

Play around with the difference variables in this pendulum sim to find out how Grace did it!

​

Length and Mass should not change the period of the pendulum.

​

See how changing Gravity changes the swing of the pendulum and see what Grace would have seen aboard the Hail Mary.