7. Gravitation

Question 1

What is Newton’s law of universal gravitation and what is the formula used?

Answer 1

It states that every particle of matter in the universe attracts every other particle with a gravitational force that is directly proportional to the product of the masses and, inversely proportional to the square of distance between them.

F = (GMm) / r^2
Force = ( Gravitational constant x Mass 1 x Mass 2 ) / separation between two particles of masses)

Question 2

What is a gravitational field?

Answer 2

It is a region of space in which a mass experiences a force due to the presence of another mass.

Question 3

Define gravitational field strength and what is the formula?

Answer 3

The gravitational field strength at a point in a gravitational field is defined as the gravitational force per unit mass acting on a test mass placed at that point.
g = F / m
gravitational force = force / mass

Question 4

Consider the earth of mass M, and a point mass of mass m, placed at a distance r from the centre of the earth. The point mass experiences a gravitational force towards the earth, what is the formula for this gravitational field strength present.

Answer 4

g = ( F x M ) / r^2

gravitational field strength = ( force x mass of earth ) / separation between the two masses

Question 5

Satellite in orbit around the earth. For circular motion to take place, the gravitation force on the satellite provides the centripetal acceleration. What is the formula in terms of velocity?

Answer 5

v = √[ (G x M) / r) ]
velocity = √[ (gravitational constant x mass of earth) / radius of earth ]

Question 6

Define gravitational potential energy and state the formula.

Answer 6

The gravitational potential energy of a mass at a point is defined as the work done by an external agent in bringing that mass from infinity to that point.

U = - ( GMm) / r
Gravitational potential energy = - ( Gravitational constant x source mass x mass attracted ) / separation between masses

Question 7

Define gravitational potential and state the formula.

Answer 7

The gravitational potential at a point in a field is defined as the work done per unit mass by an external agent in bringing a test mass from infinity to a point,

ΔU = - ( GM ) / r
gravitational potential = - ( gravitational constant x source mass ) / separation of masses

Question 8

Explain why values of gravitational potential near to an isolated mass are all negative.

Answer 8

The work done to move a mass from infinity to a point