Directions: Step 1: Watch the Newton\'s Universal Law of Gravitation and Coulomb

Question

Directions: Step 1: Watch the Newton's Universal Law of Gravitation and Coulomb's Law video. Step 2: Discuss the question in the forum. What are the similarities and differences between coulomb's force and gravitational force? Hint: You can compare and contrast the gravitational and electrical forces within the nucleus. You can also present computational analysis using Coulomb's law and the universal law of gravitation to discuss the gravitational forces at work in the nucleus, Bonus Question: Why do the repulsive forces between protons in the nucleus not tear the nucleus apart?

Explanation / Answer

Similarities between the Gravitational and Coulomb's force

1. Both are non contact forces.

2. Both can act up to infinity.

3. Both the forces depend on inverse square law

4. Both the forces are central forces.

5. Work done by both the forces is independent of path followed to move the object between two points. So they are conservative forces.

5. Both the forces can act through vaccum

6. Both the forces act along the line joining the objects under consideration.

Differences between the Gravitational and Coulomb's force

1. Gravitational force is very weak compared to Coulomb's force

2. Gravitational force is only attractive while Coulomb's force is both attractive and repulsive.

3. Electric force acts through photons while gravitational force is believed to travel in the form of gravitons.

4. Gravitational force does not depend on medium between the objects while electric force is effected by the medium present between the objects.

Let us discuss this in the case of nucleus.

Nucleus consists of both protons and neutrons.

Gravitational force exists between both the protons and neutrons.

But Coulomb's force acts only between the protons as they are charged while neutrons are unaffected by the Coulomb's force as they possess no charge.

3. Since gravitational force is weak , it does not effect the nucleons inside the nucleus even though it is attractive.

4. While neutrons are unaffected , protons stay apart due to repulsion between them as they are all like charges.

  Calculating the relative strength of both the forces

Consider two protons inside the nucleus

Both have masses m = 1.67 × 10-27 kg and charge e = 1.6 × 10-19 C

Assume that both are seperated by a distance 1 cm inside the nucleus

Gravitational force between the two protons is

F = G m m / r2

= 6.67 × 10-11 × 1.67 × 10-27 × 1.67 × 10-27 ) / ( 1 × 10-4 )

= 18.60 × 10-61 N

Coulomb's force between the two protons is given by

F' = k e × e / r2

= ( 9 × 109 × 1.6 × 10-19 × 1.6 × 10-19 ) / ( 1 × 10-4 )

= 23.04 × 1025 N

F / F' = ( 18.60 × 10-61 / 23.04 × 1025 )

= 10-36

So relative strength of gravitational force is 1036 less than Coulomb's force.

B) A strong nuclear force whose strength is 100 times more than that of Coulomb's force acts between the protons.

This attractive nuclear force keeps the protons together in a nucleus . This same force always keeps the neutrons and neutrons together and protons and neutrons together. It is charge independent

So protons cannot tear the nucleus apart.

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