Gravitational Field (DONE)

Question 1

Gravitational field equation

Answer 1

g=f/m

Question 2

Gravitational field units

Answer 2

Nkg^-1

Question 3

What is a field

Answer 3

A region where an object experiences a force

Question 4

What other units can a gravitational field have?

Answer 4

Ms^-2 (acceleration due to gravity)

Question 5

What kind of quantity is a gravitational field?

Answer 5

• vector quantity

Question 6

How to draw radial gravitational field diagram

Answer 6

• straight lines towards centre of mass

- with arrows (towards centre of mass)

Question 7

Types of gravitational field

Answer 7

• radial (drawn from centre point, the field is stronger nearer the centre of mass)
• uniform (field lines are parallel, even field strength throughout field)

Question 8

Where are gravitational fields found

Answer 8

• around any object with a mass

Question 9

How do gravitational fields of different objects interact in space

Answer 9

• attractive forces would eventually pull objects together

Question 10

What is the relationship between the size of attractive force and mass

Answer 10

Force is directly proportional to mass

Question 11

What does Newton’s third law show when talking about the attractive forces of 2 objects

Answer 11

• the attractive force of object A on object B, is equal to the force of object B on object A.

Question 12

What is the relationship between attractive force and distance between 2 centre of masses?

Answer 12

F is directly proportional to 1/(r^2)

- meaning if r (distance between centre of masses) doubles the force will quarter.

Question 13

By bringing all 3 gravitational field equations together, what is newtons law of gravitation?

Answer 13

F is directly proportional to Mm/(r^2)
Therefore:
F = -GMm/(r^2)

Question 14

What s the value of constant G?

Answer 14

6.67 x 10^-11

Question 15

What are the units of the constant G?

Answer 15

Nm^2kg^-2

Question 16

Why is the force of a gravitational field negative?

Answer 16

• because the force is attractive towards centre of mass

Question 17

What is newtons law of gravitation

Answer 17

F=-GMm/(r^2)

Question 18

Summarise newtons law of gravitation

Answer 18

• the force between 2 objects is proportional to the product of the masses and inversely proportional to their separation squared.

Question 19

What is the equation for gravitational field strength

Answer 19

g=-GM/(r^2)

Question 20

How do you derive the equation for gravitational field strength

Answer 20

1. Sub F=-GMm/(r^2) into g=f/m
Therefore:
g=-GMm/(r^2)m
2. Cancel terms
So:
g= -Gm/(r^2)

Question 21

gravitational field strengths relationship with mass is…

Answer 21

Directly proportional to mass

Question 22

What is gravitational field strengths relationship with radius

Answer 22

g is inversely proportional to r

G is proportional to 1/(r^2)

Question 23

How can gravitational field strength and radius be represented on a graph

Answer 23

r on x axis
g on y axis

• from r0 1/(r^2) relationship, line never touches x axis but gets closer and closer
• linear relationship from surface of mass towards centre of mass, gravitational field strength is zero at centre of mass

Question 24

What is the gravitational field strength at the centre of mass

Answer 24

Zero

Question 25

Summary of escape velocity

Answer 25

- the speed needed to escape the gravitational pull of a mass

Question 26

When talking about the escape velocity, what is the equation for the potential energy

Answer 26

Ep= GMm/r

Question 27

How do you derive the equation for escape velocity

Answer 27

*provided the kinetic energy exceeds potential energy Ek (kinetic energy) = Ep (potential energy) (1/2)mv^2 = GMm/r 1. Cancel m's from equation 2. V= root(2GM/r)

Question 28

What is keplers first law

Answer 28

- the orbit of a planet is an ellipse with the sun at one of two foci

Question 29

What is a foci

Answer 29

- the 2 centre points that form an ellipse

Question 30

When talking about keplers first law what does the distance from 2 foci to the same point on an ellipse equal?

Answer 30

The distance from a to point x and b to point x equals a constant for any point on an ellipse a + b = constant

Question 31

What is keplers 2nd law?

Answer 31

- a line segment joining a planet and the sun sweeps out an equal area during equal time intervals.

Question 32

What is keplers 3rd law?

Answer 32

- the square of the orbital period T, is directly proportional to the cube of the average distance from the sun r. Therefore: T^2 proportional to r^3

Question 33

What is the force causing a planet to move in a circular path?

Answer 33

- centripetal force

Question 34

What is the equation for the centripetal force?

Answer 34

F=mv^2/r

Question 35

Prove that T squared is proportional to r cubed

Answer 35

1. Use equations F=-GMm/(r^2) and F=mv^2/r 2. Substitute 3. Simplify to GM/r = v^2 4. Use S=D/T to find v=2(pie)r/T for a planet 5. Substitute v into equation (3) 6. Rearrange to find T^2= [4(pie^2)/GM]r^3 7. Therefore T squared is proportional to r cubed

Question 36

How is the centripetal force provided

Answer 36

- centripetal force is provided by the gravitational pull

Question 37

What does it mean when a satellite has a low earth orbit?

Answer 37

- the value of r is very small (close to earths surface) - some rotate at 90 degrees to earths rotation (from north to south poles) - used for: Communications Military Weather Gps

Question 38

What effect does a low value of r have on a satellite?

Answer 38

- low value of r leads to high value of v | v=root(GM/r)

Question 39

What is a geostationary satellite?

Answer 39

- satellites which orbit above equator with a time period of 24 hours equal to the speed of the earths rotation - occupy fixed portion of land - good for communications