* Gravity: The Earth exerts a force of gravity on all objects near its surface, including a ball thrown into the air.

* Unbalanced Force: When the ball is thrown upwards, the force of gravity acts downwards, opposing the upward motion. Since the force of gravity is the only force acting on the ball once it leaves your hand (ignoring air resistance), it is an unbalanced force.

* Result: This unbalanced force causes the ball to slow down as it rises, eventually stop momentarily at its highest point, and then fall back down.

Important Note: If we consider air resistance, there would be an additional upward force opposing gravity. However, in most simple physics problems, air resistance is ignored, making gravity the only unbalanced force on the ball.