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# Newton's Gravity and Escape Velocity

1. How would you describe the "use of Newton's gravity to hold the solar system together" to an elementary school child? Give some examples and situations that you might find helpful in describing gravity.

2. What is gravity? Describe gravity throughout the universe.

3. What is escape velocity? Is it the same everywhere? Why or why not?

#### Solution Preview

The equations are more clear in the attached word document.

1. How would you describe the "use of Newton's gravity to hold the solar system together" to an elementary school child? Give some examples and situations that you might find helpful in describing gravity.

The English physicist Isaac Newton introduced the term "gravity" after he saw an apple falling onto the ground in his garden and later proposed that gravity was just a particular case of gravitation. Newton's Law of Universal Gravitation states that every particle in the universe exerts a force on every other particle along the line joining their centres. The magnitude of the force is directly proportional to the product of the masses of the two particles, and inversely proportional to the square of the distances between them. In mathematical terms the force of gravitation is written as
F=GMm / R^2 ------------------------- (1)
where M and m are masses of two bodies, R is the distance between them and G is called the Gravitational Constant.

Every body on the surface of the Earth exerts a gravitational force on every other and also an equal force is exerted by Earth on them. If we are expanding this up to Sun, then Sun is also applying a gravitational force on Earth and every object on it. But the strength of the force varies. The gravitational force between Sun and Earth is more than that between Sun and a human being. This is because of the difference in the product of masses(here the distance between them is same). We can prove it by substituting the values in equation (1).

Msun = 1.98892 × 10^30 kilograms
Mearth = 5.9742 × 10^24 kilograms
Mhuman = 65 kilograms
R = 1.4959 x 10^11 metres
G = 6.6726 x 10^-11 m^3 ...

#### Solution Summary

How Newton's gravity holds the solar system together and escape velocity is explained to a child.

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