The force of gravity between them increases.
Answer:
Net force = - 1500 N
Explanation:
We calculate the net force acting using Newton's second Law:

Heat from burning fuel warms the walls of the firebox section of the furnace in
A. a hot-water heating system.
B. a hot-air heating system.
C. a compressor compartment.
D. an evaporation system.
Answer:
The atoms start vibrating really fast, making the space between them larger. It's an increase in Kinetic Energy.