A boy while playing under a mango tree saw a mango falling down. This is due to:
Gravitational force
The force due to which any matter is attracted towards the centre of the Earth is known as the force of gravity. Here, the mango falls due to the force of gravity exerted by the Earth on the mango. Once the mango gets detached from its branch, it falls down. In fact, any object which is thrown upwards, after sometimes, falls down due to gravity.