In April of 1869, he obtained a patent for one of his most important inventions, the air brake. This device enabled trains to be stopped with fail-safe accuracy by the locomotive engineer for the first time and was eventually adopted on the majority of the world's railroads
Answer:
force of gravity
Explanation:
The gravitational force between Earth and the moon is strong. But the force is not strong enough to pull the moon towards us. That's why the moon doesn't fall on Earth.