Suppose that the reaction a→products is exothermic and has an activation barrier of 75 kj/mol.

With that information you can sketch the energy of the reaction as it progresses.

You can find the sketch in the pdf file attached.

You will see that the reactants start at a certaing energy level, that level increases in 75 kJ/mol, which is the activation energy.

The intermediate products are 75kJ/mol above the energy level of the reactants.

Given that the reaction is exhotermic. The reaction will release a net heat and the products will be at a lower energy level than the reactants, which is shown by the fact that the products are placed below the level of the reactants.

If there was no gravity then their would be no downword force on the football to have it return the the grownd, and if there was no friction (mainly air friction) then there would be no opposing force the stop the ball from moving through the air allowing the ball to travle ∞.