Gravitational Forces

Question 1

what is the fundamental law of gravity

Answer 1

every particle with mass attracts every other particle with mass

Question 2

relating to the fundamental law of gravity, how are bodies such as planets or stars formed

Answer 2

• as particles with mass attract each other, they begin to clump together
• the clumps of matter attract other clumps, forming larger bodies of material each time
• these large bodies end up becoming planets or stars

Question 3

how does the speed of clumping change throughout this process

Answer 3

• initially it is very slow
• as the acceleration generated by the particles is small
• but as the clumps become larger the strength of their gravitational pull becomes more pronounced
• leading to quicker rates of clumping

Question 4

what do all particles with mass generate around themselves

Answer 4

a gravitational field

Question 5

what kind of force is gravity

Answer 5

• a distant force

- thats always attractive

Question 6

what is the basic equation for the force a body, with mass m, feels within the gravitational field of another body

Answer 6

• F = mg

- with g being the gravitational field strength of the ‘exerter’

Question 7

why doesnt this equation hold true in most realistic cases involving gravitational forces, like with the earth and moon

Answer 7

• because the body having a gravitational force exerted on it is also exerting a gravitational force on the ‘exerter’
• so the net gravitational force wouldnt just be the product of one bodys g force

Question 8

what is the true equation for the gravitational force between two masses

Answer 8

F = Gm1m2 / r^2

Question 9

what are each of the variables in F = Gm1m2 / r^2

Answer 9

• F = g force
• G = 6.67x10-11 Nm2kg-2
• m1 and m2 = masses 1 and 2
• r = distance of separation from the centres of gravity of m1 and m2

Question 10

what is the equation for centripetal force

Answer 10

F = m2 v^2 / r

Question 11

what is that m2 referring to

Answer 11

• the body experiencing the centripetal force

- between the earth and moon, it would be the moon

Question 12

what do you need to know about the relationship between gravitational force between two objects and the centripetal force an object is experiencing

Answer 12

• they are equal

- so Gm1m2 / r^2 = m2 v^2 / r

Question 13

where does that equation for centripetal force come from

Answer 13

• F = ma
• a = v^2 / r from circular motion
• so F = m v^2 / r

Question 14

what is the equation for the speed of an body orbiting another body and why

Answer 14

• v = 2 pi r / T
• comes from v = x / t
• where x is the circumference of the orbit (pi D = pi 2r)
• and T is the time it takes for one full revolution (s)

Question 15

what is usually the difference between m1 and m2

Answer 15

• m1 is the bigger object

- it is usually the main ‘exerter’