Chapter 5.4 - Gravitational Fields Flashcards Preview

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Flashcards in Chapter 5.4 - Gravitational Fields Deck (28)
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1

What causes gravitational fields

Objects having mass

2

How a spherical mass can be modelled

As a point mass

3

How do gravitational field lines work

They point in the direction that a mass would move and the closer together they are the stronger the field

4

Gravitational field strength

The force in newtons per unit mass

5

Equation for gravitational field strength in terms of forces (g=)

g=F/m

6

How are gravitational fields related to electric fields

They are both a form of a field giving rise to a force

7

What is the force between two masses proportional to

The product of the masses
The inverse square of the separation

8

Equation for gravitational field strength in terms of distance

g = -GM/r^2

9

Why do we not have to consider changing gravitational field strength when considering problems on earths surface

The change in distance is so small that the field can be considered uniform at the surface (this also applies to direction since we can consider the surface flat)

10

Relation between acceleration of free fall and gravitational field strength

They have the same numerical value (9.81) but are different things with different units

11

Keplers first law

Planets move around the Sun in an ellipse, with the Sun at one focus of the ellipse

12

Keplers second law

A line joining the Sun to a planet will sweep out equal areas in equal times

13

Keplers third law

T^2 ∝ r^3
where T is the period and r is the mean distance

14

How centripetal force relates to gravity

The centripetal force on a planet is provided by the gravitational force between it and the Sun

15

How to derive the constant for keplers third law

Equation centripetal force to the gravitational force

16

Geostationary Orbit

An orbit directly over the equator with the same angular speed as the Earths rotation, causing it to always be in the same place in the sky relative to the Earth

17

Period of a geostationary orbit

1 day

18

Uses of geostationary orbits

Telecommunications. A satellite dish can be pointed at a geostationary satellite and can remain stationary because the satellite is stationary relative to the Earth

19

How to calculate the orbital radius of a geostationary satellite

Keplers third law with the constant

20

Gravitational potential at a point

The work done to bring a unit mass from infinity to that point

21

Gravitational potential at infinity

0

22

How to calculate the energy required to move an object over a gravitational potential difference

W=mΔV
where V is the gravitational potential

23

What a force-distance graph for gravitational force from a sphere mass looks like

1/x
x > r where r is the radius of the sphere

24

Area under a force-distance graph

Work done to move the object between the two points

25

What is gravitational potential energy (over large distances) proportional to

Product of the masses
inverse of the distance

26

Escape velocity

Minimum velocity required to escape a gravitational field i.e. the kinetic energy of the object is equal to the magnitude of its gravitational potential energy

27

How to calculate escape velocity

KE=GPE

28

How gravity relates to atmospheric thickness

The more massive a planet is the more kinetic energy will be needed to overcome its gravitational energy and therefore a higher escape velocity will be required, making it less likely that a particle will reach this velocity and escape. Therefore more massive planets have thicker atmospheres.