Gravitational Fields

Question 1

how would you draw the gravitational field lines around a point of mass

Answer 1

• the arrows would be drawn perpendicular to the surface of the point
• and the arrows would be pointing towards the point of mass

Question 2

why are the perpendicular lines an accurate way of presenting the gravitational field of a point of mass

Answer 2

• the distance between the lines increase the further away you get from the mass
• correctly indicating a decrease in the strength of the gravitational field

Question 3

why are the arrows an accurate way of presenting the gravitational field of a point of mass

Answer 3

• it shows the direction the gravitational force is acting towards
• which also indicates the direction any other mass within its g field would be accelerating to

Question 4

what is the equation for the field strength of a body with mass M

Answer 4

g = GM / r^2

Question 5

what is gravitational potential energy

Answer 5

• the energy an object possesses

- by virtue of its position within a gravitational field

Question 6

what is the definition of gravitational potential

Answer 6

• the amount of work done per unit mass

- to move an object from an infinite distance to a certain point within a g field

Question 7

what is the equation for gravitational potential

Answer 7

V(grav) = -GM / r

Question 8

why is the value of V negative

Answer 8

• because gravitational fields are attractive
• so objects gain energy when moving into a point in the field
• think of it like this: when youre very close and r is small , you get a ‘big’ negative value (eg -10)
• but when youre far away and r is big you get a ‘small’ negative value (eg -5)
• this means the object is 5 energy units closer to escaping its pull
• the closer you get to 0, the further away you are and the weaker the pull

Question 9

if gravitational field strength is telling us the rate at which gravitational potential is changing over a distance, what is the relationship between gfs and gp

Answer 9

• you can differentiate gfs to get gp
• g = -dV(grav) / dx
• where x is the distance

Question 10

how could you use this relationship to calculate the change in gp over small distances

Answer 10

• because g doesnt change significantly over small distances
• you can say g = -delta V(grav) / delta x
• then rearrange to g delta x = -delta V(grav)

Question 11

what do all these equations eventually lead to

Answer 11

• the equation for GPE

- GPE = mg delta x (h)

Question 12

why are the equations for calculating things such as force, field strength and potential so similar between gravitational and electric fields

Answer 12

• because both types of fields are radial from a point

- so the bodies interact in similar ways

Question 13

other than the change in symbols, what is the main difference between the electric field and gravitational field equations

Answer 13

their constants of proportionality

Question 14

what is the constant for electric field equations

Answer 14

• the coulomb law constant, k

- k = 1 / 4 pi e(0) = 9x10^9

Question 15

between the electromagnetic force and the gravitational force, which one is stronger

Answer 15

the electromagnetic force