Please Help!!?

At low temperatures, the kinetic energy of the particles is small on average, allowing the attractive forces between them to bind them together into, say, a solid. When the substance is heated, the particles gain kinetic energy, and once this is sufficient to overcome the attractive forces, the binding effect breaks down - leading to a liquid. The same thing occurs during the liquid to vapor transition - now the molecules become essentially free from each other.

Every two particles in the universe are attracted to each other by Newton's Law of Universal Gravitation #F_G=G{m_1m_2}/{d^2}#. That is one type of attractive force.

When energy is added to a system, particles will begin to move and the distance between some particles increases, resulting in #F_G# decreasing. These particles bounce into each other, therefore creating friction, therefore resulting in an increase in heat. Of course as some particles move farther apart, some particles move closer together, but the overall affect of adding heat is the distance between particles increases.