An object thrown upward loses approximately 9.8 meters per second (m/s) in speed each second due to gravity. This is known as the acceleration due to gravity, and it's represented by the symbol g.

Here's why:

* Gravity pulls objects down: Gravity exerts a constant force on objects near the Earth's surface, pulling them downwards.

* Acceleration is a change in speed: This force causes the object's upward velocity to decrease over time.

* Constant acceleration: The rate at which the object slows down is consistent, approximately 9.8 m/s².

Important Note: This value is an approximation. The actual acceleration due to gravity varies slightly depending on factors like altitude and latitude.