3.2 Newton's Law of Universal Gravitation

Question 1

Newton’s Law of Universal Gravitation is what law?

Answer 1

Inverse square law between force and distance.

Question 2

A graph of F against r gives what shape graph?

Answer 2

An exponential decay

Question 3

A graph of F against 1/r^2 gives what graph?

Answer 3

A straight line

Question 4

What does the Newton’s Law of Universal Gravitation help work out?

Answer 4

The force experienced by a mass when it in the gravitational field of point mass

Question 5

Is force a vector?

Answer 5

Yes

Question 6

What is the equation displaying this laws?

Answer 6

F  = Gm1m2/r^2 
F = gravitational force 
G = gravitational constant (6.67x10^-11) 
m1 = mass creating field 
m2 = mass feeling force in the field 
r =  separation of m1 and m2 (from their centres if sphere)

Question 7

Is the force between m1 due to m2 the same as the force on m2 due to m1?

Answer 7

Yes, but opposite

Question 8

What is a point mass?

Answer 8

A theoretical object that has mass but no dimensions so we assume all mass is concentrated at the centre

Question 9

What do the gravitational field lines show?

Answer 9

The direction of the force a mass would feel in a gravitational field of object creating it

Question 10

Why are gravitational forces usually very small?

Answer 10

As only object of great mass have a great enough gravitational field strength to show much effects

Question 11

When not using point masses what do we get for the value of the force

Answer 11

An estimate

Question 12

A body which only has one force acting on it, which is the gravitational force of the earth or planet they’re near are said to be in what state?

Answer 12

A state of free fall

Question 13

What objects which orbit the earth are in the state of free fall?

Answer 13

Satellites , natural and artificial

Question 14

What are some artificial satellites?

Answer 14

communications satellites, weather satellites, military ones and International Space Station.

Question 15

What is the earth’s only natrual satellite?

Answer 15

The moon

Question 16

What does it mean if a satellite is geosynchronous?

Answer 16

A satellite which remains in the same space relative to the earth, this means they lie in an equatorial plate and complete 1 revolution per 24 hrs.

Question 17

Mixing equation for centripetal force and Newton’s Law of Universal Gravitation gives us what?

Answer 17

mv^2/r = Gm1m2/r^2 and v = 2πr/T

this leads to r^3 = Gm1T^2/4π^2

Question 18

What is this equation often known as?

Answer 18

Kepler’s Third Law

Question 19

What does Kepler’s Third Law tell us?

Answer 19

That the further the satellite is from the thing creating the gravitational field the longer it takes to orbit.

Question 20

What is weightlessness?

Answer 20

A state in which the only force acting on the object is the pull of the earth or nearby planets for a longer amount of time. This means object can float around