Universal Gravitation

Question 1

Uniform gravitational fields

Answer 1

• Close to earths surface field appears uniform, field lines are parallel and evenly spaced
• strength of uniform field determined by g= Gravitational Force/Mass
• Objects in free fall will fall with acceleration of ‘g’ ms^-2

Question 2

Equipotential Surfaces

Answer 2

• an imagined ‘surface’ where (gravitational) potential doesn’t change when an object moves along it. Potential only changes when objects move up/down between surfaces

Question 3

Radial gravitational fields

Answer 3

• Field appears radial when observed from above the earth, so g decreases w/ height
• Earths surface is a place where gravitational potential is 0 (equipotential surface)
• change in G.P = g*change in height
• g (in radial fields) = G*mass being orbited round/radius^2

Question 4

Gravitational force between 2 masses

Answer 4

• F= Gmass of object 1(being orbited round)mass of object 2(in orbit)/radius^2
• G = gravitational constant = 6.67*10^-11
• as F is proportional to 1/r^2, it decreases w/ distance but never reaches 0
• radius is to the centre of spherical objects, cannot work on irregular shapes (will give estimate though)

Question 5

Velocity

Answer 5

• velocity^2 = G*mass of object 1/radius

- velocity = 2piradius/Orbital Time

Question 6

Kepler’s third law

Answer 6

• radius^3 = Gmass of object 1 (being orbited around)orbital time/4*pi^2
• can calculate Orbital Time and Radius of a satellites orbit with only the earths mass

Question 7

Satellite types

Answer 7

• Low polar satellites orbit as low as they can without being slowed down, which for earth is about 6470 km
• good for larger, wide aerial photos
• Geostationary Satellites orbit with an orbital period of 24 hrs around the equator, so they orbit at the rate earth rotates and don’t appear to move

Question 8

Gravitational Potential

Answer 8

• V(grav) = Gravitational potential = -G*mass being orbited/r
• G.P.E = V*mass in orbit = -GMm/r