3.7.2 Gravitational fields

Question 1

Properties of Gravity/Gravitational force

Answer 1

• Acts on objects with mass
• Always attractive

Question 2

Newtons’s Laws of gravitation

Answer 2

• Directly proportional to the product masses
• Inversely proportional to the square of the distance between them

Question 3

Gravitational Force Equation

Answer 3

F = (G * m1 * m2) / r²

Question 4

Relationship between Mass and gravitational force

Answer 4

Larger masses exert greater gravitational force

Question 5

Relationship between distance and gravitational force

Answer 5

Greater distance results in weaker gravitational force

Question 6

Uniform Field

Answer 6

• Same gravitational force everywhere
• Represented by parallel, equally spaced field lines

Question 7

Radial Field

Answer 7

• Force varies with position
• Field lines spread out as distance increases

Question 8

Field Lines

Answer 8

• Direction of force on mass
• Closer lines indicate stronger force

Question 9

Earth’s Gravitational Field

Answer 9

• Radial in nature
• Nearly uniform close to the surface

Question 10

Gravitational Field Strength (g) (definition and variability)

Answer 10

Definition
* Force per unit mass exerted by a gravitational field

Variability
* Constant in uniform fields
Varies in radial fields

Question 11

Formulas for Gravitational Field Strength

Answer 11

General Formula
* g = F / m

Radial Field Formula
* g = (G * M) / r²

Question 12

Gravitational Potential

Answer 12

• Work done per unit mass
• Moving an object from infinity to a point

Question 13

Gravitational potential at infinity

Answer 13

Zero

Question 14

Is the Gravitational Potential positive or negative

Answer 14

Always negative due to energy release

Question 15

Gravitational potential formula

Answer 15

Question 16

Gravitational Potential Difference (ΔV)

Answer 16

Energy needed to move a unit mass between two points

Question 17

Gravitational Potential Difference (ΔV) equation

Answer 17

Question 18

Equipotential Surfaces

Answer 18

• Surfaces of equal gravitational potential
• Constant potential across the surface
• No work done when moving along these surfaces
  * since gravitational potential difference = 0

red lines are equipotential surfaces

Question 19

V vs r relationship

Answer 19

gravitational potential(V) Inversely proportional to the distance between the centres of the two objects (r)

Question 20

1.

area under g vs r graph

Answer 20

• gravitational potential difference
• Typically shows a decrease as distance increases.

Question 21

Kepler’s Third Law

Answer 21

Square of orbital period (T) is directly proportional to the cube of radius (r)

Question 22

How would you derive the equation

Answer 22

• Centripetal Force = Gravitational Force
• Rearrangement to find velocity (v)
• Substitute v² into gravitational equation
• (4π² / GM) is a constant

Question 23

What is the total energy of a satellite

Answer 23

• Kinetic Energy + Potential Energy
• Constant total energy in orbit

Question 24

Escape velocity

Answer 24

Minimum velocity to escape gravitational field

Question 24

Synchronous Orbit

Answer 24

Orbital period equals rotational period of the planet

Question 25

Equation for escape velocity

Answer 25

Question 26

Geostationary Satellites

Answer 26

• Specific type of synchronous orbit
• Always above the same point on Earth
• Useful for communication (TV, telephone)

Question 26

Calculating Geostationary Orbit

Answer 26