A non-contact force is a force that acts on an object without coming into contact with it. For a contact force to act on an object it must have physical contact with it. Gravitational force causes the football to fall back toward the ground after it is thrown. Is gravitational force a contact or non-contact force?

non-contact force

Explanation:

Gravitational force is considered a non-contact force because gravitational force does not require any physical contact with an object and it is an attractive force.

in the given example the football will fall back towards the ground without any physical contact between the ground and the ball and it is only the attractive force of gravity of the ground that pulling the ball back to the ground.

Hence, the correct answer is "gravitational force is a non-contact force".

explanation:

let the different atoms be x and y. each with four protons and same mass will be represented as follows.

mass number is number of protons + number of neutrons.

            and  

since, it is given that one has a negative charge while the other is neutral. therefore, there will be increase in number of protons and the atom will be represented as follows.

according to periodic table, mass number of beryllium is 9 and it has atomic number 4 so, the atoms will be and .  

the protons and neutrons will be located inside the nucleus whereas the electrons will be revolving around the nucleus.