gravitational + electric fields (not implemented ef yet)

Question 1

what is the equation for gravitational force [Newton’s law of gravitation], using: G, M, m and r?
GF

Answer 1

F = - GMm / r^2

where:
• G = universal gravitational constant
• M = mass of body that is being orbited
• m = mass of body that is orbiting another body
• r = distance from one body’s centre to another body’s centre

there is a (-) bc grav force is an attractive force

Question 2

what is the definition template for gravitational or electrostatic force?
GF + EF

Answer 2

[gravitational / electrostatic] force is proportional to product of [masses / charges] and inversely proportional to the square of their separation

Question 3

what is the equation for gravitational field strength, using: G, M and r?
GF

Answer 3

g = - GM / r^2

where:
• G = universal gravitational constant
• M = mass of body
• r = distance from body’s centre to point in its gravitational field

g is NOT a force, it is the force you would feel at that point

Question 4

how do we get from grav F to g?
GF

Answer 4

divide by m

F = - GMm / r^2 => ÷m => g = - GM / r^2

Question 5

what is the equation for gravitational potential energy, using: G, M, m and r?
GF

Answer 5

GPE = - GMm / r

where:
• G = universal gravitational constant
• M = mass of body being orbited
• m = mass of body orbiting (the other body)
• r = distance from centre of one body to centre of another body

Question 6

how do you get from grav F to GPE?
GF

Answer 6

multiply by r
(which means that work is done, bc Fd = W)

F = - GMm / r^2 => x m => GPE = - GMm / r

Question 7

what is the definition for Vg?
GF

Answer 7

Vg (gravitational potential) is the work done in moving a unit mass from infinity to a point in the gravitational field

Question 8

what is the equation for Vg, using: G, M and r?
GF

Answer 8

Vg = - GM / r

where:
• Vg = gravitational potential
• G = universal gravitational constant
• M = mass of body
• r = distance from centre of body to point in gravitational field

Question 9

how do we get from GPE to Vg?
GF

Answer 9

divide by m

GPE = - GMm / r => ÷m => Vg = - GM / r

Question 10

what is the equation for change in gravitational potential energy, using: m and Vg?
GF

Answer 10

ΔGPE = mΔVg

where:
• mass of body that is orbiting another body
• Vg = gravitational potential

Question 11

how to get from g to Vg?
GF

Answer 11

multiply by r

=> g = - GM / r^2 => x r => Vg = - GM / r

Question 12

what is the equation for g, using: Vg and r?
GF

Answer 12

g = ΔVg / Δr

where:
• Vg = gravitational potential
• r = distance from centre of body to point in gravitational field

so g can also be called a potential gradient => the higher the gradient, the stronger the force you feel