Explain motion under gravity.

Hint: Gravity is a force that is applied by every planet to pull the object towards its centre. This also applies to Earth. Earth pulls us all towards its center. This is the reason we all stick on this planet and not fall in space.

Complete step by step answer:
Newton gave laws of gravitation when an apple fell on his head. Gravitation is present for all the bodies that have some mass in it. Every object having some mass pulls every other object towards itself. Large masses attract more compared to small ones.
Earth being a huge mass body attracts us all towards itself. Every motion on Earth is affected due to the gravitation of Earth.
A body can be said to be in free fall when it is dropped from a certain height and is allowed to fall under the effect of gravity. The moment a body is dropped, a force of gravity due to Earth pulls it towards its centre.
We know from Newton’s laws that whenever a body is acted upon by a force, there must be a certain value of acceleration with the body. This acceleration in case of gravitation is known to be acceleration due to gravity.
Even when a body is thrown in a horizontal direction, then also due to gravity, it will not go horizontally but will curve its path to form a parabola. This motion is termed as projectile motion.

Note:
Remember that as Earth attracts everybody towards itself so does the object. The object pulls Earth towards but as the mass of the object is negligible compared to that of Earth, the force is also negligible.