A isotope is atoms of the same element with different amount of neutrons to change the mass. They can become more stable by sharing or giving away electrons to have a stable electron shell
That force would be gravity. Gravity is what pulls any object down towards Earth due to the large mass of the Earth.
The two substances have different densities. Density can be affected by the temperature of a substance. Since they have to same volume but weigh differently, they have different densities. Remember, density = mass/volume
A virus is a pathogen that can't reproduce by itself. What they do is enter another cell an uses the cells natural reproduction system to reproduce the virus as well. Essentially the virus is feeding off a living cell.
Hope this helped!
