Gravitational Fields

Question 1

What is gravitational field?

Answer 1

A region in which an object with mass will experience the force of gravity

Question 2

Properties of gravitational fields

Answer 2

• Any object with mass produces a gravitational field
• Gravitational field lines extend to infinity
• Field lines are directed towards the object generating them
• Gravitational field lines show the direction of the resultant force and the path an object with mass would take if places in the field

Question 3

What the difference between a Gravitational and Electric field?

Answer 3

Gravitational fields are always attractive whereas an electric field can be attractive and repulsive

Question 4

What is Gravitational Field Strength?

Answer 4

The force experienced per unit mass at a given point in the field

Question 5

Units for g (Gravitational Field Strength)

Answer 5

N kg-1

Question 6

What is the law of gravitation

Answer 6

The gravitational force between 2 objects is directly proportional to the mass of each object and inversely proportional to the square of the distance between their centres

Question 7

What does the negative symbol in the gravitational force equation indicate

Answer 7

That the gravitational force is positive

Question 8

What is the Gravitational Field Strength at the Earths surface?

Answer 8

9.81 N kg-1

Question 9

How to you calculate the Gravitational Field Strength at any distance r from an object

Answer 9

g = - GM/r^2

Question 10

What is M and m

Answer 10

M = mass of the object causing the field
m = mass of the object experiencing/in the field

Question 11

Keplers 1st law

Answer 11

The orbit of a planet is elliptical, with the Sun at one of its foci

Question 12

Keplers 2nd law

Answer 12

A line segment joining the Sun and a planet/comet sweeps out equal areas in equal time intervals

Question 13

Keplers 3rd law

Answer 13

The square of a planet’s orbital period, T, is directly proportional to the cube of its average distance from the Sun, r, ie: T^2 = r^3
K = T^2 / r^3

Question 14

Geostationary satellites

Answer 14

• Orbit the equator
• Focused on a specific part of the Earth at all times
• Must travel in same direction as Earth’s spin
• Orbital height: same for all
• Orbital period: 24 hours
• Uses: communications, sat-nav GPS, local weather

Question 15

Polar orbiting satellites

Answer 15

• Orbit over the poles and will cover the whole Earth
• Orbital height: 100 - 200 km;
• Orbital period: approx. 90 mins
• Uses: global weather, climate observations, defence/military

Question 16

What is Gravitational potential

Answer 16

Gravitational potential is the work done per unit mass to move an object from infinity to a given point in a gravitational field where the gravitational potential at infinity is 0 Jkg^-1)

Question 17

What is Gravitational potential energy

Answer 17

Gravitational potential energy is the total work done to move an object of mass m from infinity to a point in a gravitational field

E= mV
E = - GMm/r

Question 18

What is Gravitational potential

Answer 18

Gravitational potential is the work done per unit mass to move an object from infinity to a given point in a gravitational field where the gravitational potential at infinity is 0 Jkg^-1)