Galileo proves that gravity is a force.
Just like magnetism is a force, the wind is a force.
Forces are not energy.
All forces in the universe are caused by energy imparting itself (on another object).
The combustion engine ignites fuel (energy) to propel the drive shaft and thus the car (the resulting force) and if it hits another car it will impart its force onto another car forcing it forwards as well.
As all forces in the universe are caused by energy so gravity is also caused by energy.
Einstein tells us that gravity is a warp on the fabric of space time.
Therefore energy in some concentration (matter / mass) collides with space-time causing the force of gravity.
It is too constant to be random collisions between energy and the fabric of space-time, instead we can assume some ordered interaction between mass-energy and space-time similar to electricity and magnetism however their may be no residue effect of the gravity such as with magnetism so we shall assume that it is two opposing forces of different powers the result being gravity as we believe the universe is expanding as a force.