Gravity and Weight

The Earth's core is the reason why Gravity exists, gravity is a force that attracts objects together and relies on mass as well as the distance between the two objects,
that is why when you travel in the ozone layer gravity is weaker. 

Everything has a gravitational force pulling things towards it, like an apple and a skyscraper, there is a gravitational pulling the apple and skyscraper together but it is so slight that it is practically non-existent. 

For large objects, or in this case.
Planets, have a much stronger gravitational pull than an apple, having a file of influence around it. We, humans, have dubbed this a "Gravitational field" and the strength is the "Gravitational field strength" In, in Physics we show the letter "g" as gravity, which if we are talking about Earth is around 9.8 newtons per kilo, but if you take the moon it would be 1.6 newtons per kilo because the moon is smaller and thus has a smaller mass.

So whenever an object comes into a gravitational field it is attracted or pulled towards the gravitational field, so to calculate an object's weight, we take its mass and multiply it by the gravitational field strength (9.8) so if someone weights 60kg, we multiply 60 * 9.8 giving us 588 newtons or 588N. For this, we would say we have a weight of 60kg, not a mass of 60kg.
Mass refers to the basic characteristic of the object's mass, and Weight is how much the force of gravity affects it.

When you jump you are expending energy and putting it in the "Gravitational potential energy store", the formula for gravitational potential energy store is 
Ep = mgh or Mass * Gravitational field strength * height the measurements are mass (kilos), gravitational field strength (newtons per kilo) and H (Height), and Ep is measured in Joules.

Now let's take an apple with a mass of 100 grams and we throw it 3 meters into the air.
First, we have to convert the mass to kilograms to make the equation easier, so we convert the 100g to 0.1kg by dividing the 100g by 1000 (because one kilo is 1000 grams). Then we multiply the 0.1 (weight) * 9.8 (the gravitational field strength) * 3 meters (height), and we get 2.94 joules of energy.

Once again gravity relies on the mass of an object and how far it is from other objects, so planets will attract space debris, but rocks cannot attract other rocks on earth, because of the mass difference between a planet and a rock.