Topic 8 : Gravitational fields Chapter 18

Question 1

According to Newton, all masses create a………

Answer 1

gravitational field in the space around them.

Question 2

what does the arrows and spacing of the field line represent?

Answer 2

the arrows - represent the direction of the gravitational force on a mass placed in the field.
the spacings- indicates the strength of the gravitational field. —-> the further apart the field lines are, the weaker the field.

Question 3

what is the direction of the field lines of an object placed in Earth’s gravitational field?

Answer 3

all objects are attracted towards the centre of the earth.

Question 4

what is a point mass body?

Answer 4

if a body covers a very large distance as compared to it’s size, then to study its motion, its size and dimension can be neglected; and the object can be regarded as point mass body.

Question 5

what is the shape of the Earth’s gravitational field strength?

Answer 5

the Earth’s gravitational field is radial.

Question 6

what is the shape of the Earth’s gravitational field strength on a scale of building?

Answer 6

the gravitational field is uniform.

Question 7

describe Newton’s law of gravitation using Newton’s third law of motion.

Answer 7

all masses create a gravitational field in the space around them.

when two point masses are kept at a distance of r from each other. both will attract each other with a force F.

(According to Newton’s third law of motion, point masses will interact and and exert an equal and opposite force on each other.)
therefore, when mass A attracts mass B with a force F. mass B will attract mass A with force B. —refer to fig 18.7 pg no. 274

Question 8

what is Newton’s law of gravitation?

Answer 8

any two points masses attract each other with a force that is directly proportional to the product of their masses and indirectly proportional to the square of their separation.

F ∝ Mm
F ∝ 1/r^2

Question 9

what would happen if the centre-to-centre distance between two masses is equal to the sum of their radii?

Answer 9

this means the masses would be touching externally. therefore their separation distance would be 0. and hence, F would be undefined.

Question 10

what is the gravitational constant ?

Answer 10

universal gravitational strength

G = 6.67 * 10^-11 N m^2 kg^-2

Question 11

how can we find the magnitude of the gravitational force attracting two masses?

Answer 11

F = (mMG) / r^2

Question 12

what is the direction of the gravitational force acting on two masses?

Answer 12

the force is attractive.

it will be towards the other mass, i.e, in opposite direction of separation r.