ch17 - gravitational fields

Question 1

gravitational field strength

Answer 1

the gravitational force exerted per unit mass on a small object placed at that point

Question 2

field lines show:

Answer 2

. arrows show direction for gravitational force on a mass placed in the field
. spacing of the field lines she the strength of the gravitational field (more distance = more surface area = more weak)

Question 3

point of Earth’s gravitational force

Answer 3

centre

Question 4

centre of mass

Answer 4

the point at which we can consider the total mass of the object to be concentrated

Question 5

close to surface, Earth’s gravitational field is

Answer 5

linear

Question 6

far from surface, Earth’s gravitational field is

Answer 6

radial

Question 7

Newton’s lae of gravitation

Answer 7

any two point masses attract each other with a force that is:
. directly proportional to Mm
. inversely proportional to r²

Question 8

F proportional to Mm/r²

Question 9

F = GMm/r²

Question 10

G

Answer 10

gravitational constant
G = 6.67 * 10^-11 Nm²kg-²

Question 11

gravitational field strength due to a point mass derivation

Answer 11

g = F/m
g = GMm/r²m

g = GM/r²

(M = mass of body causing the field)

Question 12

gravitational field strength formula

Answer 12

g ≈ 9.81 N/kg

Question 13

gravitational field strength is scalar or vector

Answer 13

vector

Question 14

gravitational field strength and r

Answer 14

inversely proportional

Question 15

g

Answer 15

acceleration of free fall - m/s²
gravitational field strength - N/kg

Question 17

% change in R

Answer 17

<>R/ R * 100%

Question 18

% change in g

Answer 18

<>R/ R * 2* 100%

Question 19

why can’t we use gpe = mgh

Answer 19

. assumes gpe = 0 on Earth surface
. if lifted to great height, g will decrease - g not always constant

Question 20

where is gpe 0

Answer 20

at infinity

Question 21

gravitational potential/gpe

Answer 21

work done per unit mass in bringing a point mass from infinity

Question 22

gravitational potential always

Answer 22

negative

Question 23

orbital period

Answer 23

time taken by object (such as planet) to complete one orbit

Question 24

gravitational potential formula

Answer 24

o/ = - GM/r

Question 25

moving closer to body with gravity

Answer 25

less gpe, less potential

Question 26

difference in gravitational potential

Answer 26

<> o/ = GM (1/r1 - 1/r2)

Question 27

difference between field strength and potential

Answer 27

field strength = force potential = potential energy

Question 28

orbiting, when gravity is Fc

Answer 28

GMm/r² = mv²/r v² = GM/r M of planet

Question 29

orbital period

Answer 29

time taken by an object to complete one orbit

Question 30

v = 2pi * r / T

Question 31

T and r relation

Answer 31

T² proportional to r³ (2pi *r/T)² = GM/r

Question 32

artifical satellite orbit types

Answer 32

. circular - close view, 16orbits in one day . elliptical - distant view . geostationary - orbits at same angular speed as Earth

Question 33

geostationary orbit

Answer 33

an orbit of a satellite such that the satellite remains directly above the same point of the Earth at all times

Question 34

geostationary orbit uses

Answer 34

. telecommunications . satellite TV transmissions

Question 35

geostationary satellite lifespan

Answer 35

10 years (run out of fuel)