gravity

definition: 
The force that attracts a body towards the centre of the earth, or towards any other physical body having mass
sentence: 
Objects exert a force of gravity because they have mass and the more mass they have the stronger the force of gravity they exert. Physics has found only four forces in nature: gravity, electromagnetism, weak nuclear, and strong nuclear.
difficulty: 
easy
toefl frequency: 
2
toefl classification: