You're thinking about Newton's Third Law of Motion! It's true that when you jump off a branch, you exert an upward force on the Earth. This is because every action has an equal and opposite reaction.

Here's the breakdown:

* Your action: You push down on the Earth with your feet as you jump.

* Earth's reaction: The Earth pushes back on you with an equal and opposite force, propelling you upward.

Why we don't notice Earth's acceleration:

* Mass difference: The Earth is incredibly massive compared to you. The force you exert on it is minuscule compared to its own mass.

* Inertia: Earth has enormous inertia, meaning it resists changes in its motion. The tiny force from your jump doesn't significantly affect its velocity.

* Earth's acceleration is too small to perceive: Even if you could measure Earth's acceleration, it would be incredibly small, far below our ability to detect it.

Analogy:

Imagine a tiny fly landing on a giant truck. The fly exerts a force on the truck, but the truck doesn't noticeably move. It's the same principle. The force you exert on Earth is like the fly's force on the truck.

In conclusion: You do indeed exert a force on Earth when you jump, but because of the massive difference in mass and inertia, the resulting acceleration of Earth is practically unnoticeable.