5.4 Gravitational fields

Question 1

Gravitational Field

Answer 1

the region around a body in which other bodies will feel a force to the mass of the body

Question 2

Gravitational Field Lines

Answer 2

show the shape of the field and the direction in which a small mass would move if placed in that point in the field

Question 3

Gravitational Field Strength (Definition)

Answer 3

the force acting per unit mass at that point

Question 4

Gravitational Field Strength (Equation)

Answer 4

g= F/m

Question 5

Newton’s law of gravitation (Definition)

Answer 5

the gravitational force of attraction between two point masses is directly proportional to the product of their masses and inversely proportional to the square of their separation

Question 6

Newton’s law of gravitation (Equation)

Answer 6

F=(-GMm)/(r^2)

Question 7

What assumption do we make about spherical masses?

Answer 7

A spherically symmetrical mass can be considered as a point mass if all its mass is concentrated in the centre

Question 8

Make an equation with g G M r

Answer 8

g=F/m
F=(-GMm)/(r^2)
g=(-GM)/(r^2)

Question 9

Kepler’s third law (Definition)

Answer 9

the square of the period of a planet orbiting the sun is proportional to the radius of its orbit cubed. Also applies to other planetary systems, the orbits of moons, and binary stars

Question 10

Geostationary orbit

Answer 10

The orbit of Earth made by a satellite that has the same time period and orbital direction as the rotation of the Earth and is in the equatorial plane.

Question 11

Kepler’s three laws (List)

Answer 11

1. Planets travel around the sun in elliptical orbits
2. A line joining the sun to a planet will sweep out equal areas in equal times
3. the time period of an orbit is proportional to the radius of the orbit cubed

Question 12

Uses of geostationary satellites

Answer 12

Weather/environment measuring
Broadcasting TV signals
Relaying mobile phone signals
Monitoring air traffic

Question 13

Gravitational Potential

Answer 13

the work done in moving unit mass from infinity (where gp is 0) to that point. units are Jkg^-1

Question 14

Gravitational Potential Energy

Answer 14

Gpe of a mass, m, in a field depends on its position in the field. For a radial field arounds a point mass M, the gpe at a distance r from M is -GMm/r

Question 15

Escape Velocity

Answer 15

The minimum launch velocity required to move an object from that point to infinity