Book page 257 - 262

copycg

rah

amp

hys

ics

com

20

16

What is gravity

bull Gravity - Official Main Trailer [2K HD]-windowswmv

copycg

rah

amp

hys

ics

com

20

16

What is gravity

bull Gravity - Official Main Trailer [2K HD]-windowswmv

copycg

rah

amp

hys

ics

com

20

16

Why do things fall

bull Aristotle Things reach their natural resting position

bull Newton All masses exert an attractive force on other masses

bull Einstein Gravitational field is a distortion of space and time

copycg

rah

amp

hys

ics

com

20

16

Changing theories

bull Newtonrsquos field theory

bull Masses create gravitational field around them

bull Field exerts force on any mass placed in it

bull Near Earth = center of Earth

bull Einsteinrsquos field theory

bull Space and time is curved near an object

bull The second object will move on the shortest path

copycg

rah

amp

hys

ics

com

20

16

Definitions

Force field

bull A region where a force acts

bull Strength of field varies with distance of central mass

Field theory

bull Original force at a distance without interaction

bull Field cannot directly be observed only measured by its effect on masses

bull Modern view quantum field theory

bull Force is transmitted between masses when exchanging ldquovirtualrdquo gravitons

bull Not observed yet

copycg

rah

amp

hys

ics

com

20

16

Representing gravitational field

bull It exerts forces at any point within the field

bull Must have strength and direction

bull Described by gravitational field strength ldquogrdquo

bull ldquogrdquo ne gravity

bull When masses are moved in a gravitational field their PE in the field changes

bull This is called gravitational potential

copycg

rah

amp

hys

ics

com

20

16

Gravitational field strength

bull Gravitational field strength is the gravitational force exerted per unit mass at a point in the field

bull 119892 =119865

119898

bull Units N119896119892minus1

bull Field strength is a property of the field

bull It depends on a test mass

bull A test mass is small so its effects on the field can be ignored

Red shows higher ldquogrdquo

copycg

rah

amp

hys

ics

com

20

16

Field lines bull Field lines point in the direction a free body would begin to

accelerate if released

bull Density of field lines they are a measure of field strength which is equivalent to free fall acceleration at that point

bull 119892 =119865

119898=

119898119886

119898= 119886

bull All field lines come from infinity and end on masses

copycg

rah

amp

hys

ics

com

20

16

Universal law of gravitation

bull Every material particle in the Universe attracts every other material particle with a force that is directly proportional to the product of the masses of the particles and inversely proportional to the square of the distance between them

bull G= 667times 10minus11119873119898minus2119896119892minus2

copycg

rah

amp

hys

ics

com

20

16

Forces obey Newtonrsquos 3rd law bull Forces are equal and opposite

bull Mass is gravitational mass

bull 119877 ne distance between centre of masses but it is a force law between particles and not objects or masses

bull Newton deduced that spheres of mass follow the same law where the separation is between their centers

bull Example How fast does the apple drop

Assume apple weighs 1g and Earth 598 times 1024kg The radius of Earth is 64119909106m

bull 119892 =119865

119898=

119866119872119898

1198772119898=

119866119872

1198772=

667times10minus11times598times1024

64119909106 2

bull 119892 = 974119898119904minus2

bull This is the acceleration due to the gravitational field

copycg

rah

amp

hys

ics

com

20

16

ldquogrdquo has two different units bull F = ma where g = a

bull ldquogrdquo is N119896119892minus1 or m119904minus2

bull N119896119892minus1 is used if explicitly dealing with field strength 119892 =119865

119898

bull 119865119892 =119866119872119898

1198772 gravitational force

bull Remember gravitational field intensity near a point mass in N119896119892minus1

119892 =119865

119898=119866119872119898

1198772119898=119866119872

1198772

bull Law deals with point masses

bull Forces acting on masses are equal and opposite

bull Forces are always attractive

bull Forces are between all objects but only significant if objects involved are massive

copycg

rah

amp

hys

ics

com

20

16

Changing theories

bull Newtonrsquos field theory

bull Masses create gravitational field around them

bull Field exerts force on any mass placed in it

bull Near Earth = center of Earth

bull Einsteinrsquos field theory

bull Space and time is curved near an object

bull The second object will move on the shortest path

copycg

rah

amp

hys

ics

com

20

16

Definitions

Force field

bull A region where a force acts

bull Strength of field varies with distance of central mass

Field theory

bull Original force at a distance without interaction

bull Field cannot directly be observed only measured by its effect on masses

bull Modern view quantum field theory

bull Force is transmitted between masses when exchanging ldquovirtualrdquo gravitons

bull Not observed yet

copycg

rah

amp

hys

ics

com

20

16

Representing gravitational field

bull It exerts forces at any point within the field

bull Must have strength and direction

bull Described by gravitational field strength ldquogrdquo

bull ldquogrdquo ne gravity

bull When masses are moved in a gravitational field their PE in the field changes

bull This is called gravitational potential

copycg

rah

amp

hys

ics

com

20

16

Gravitational field strength

bull Gravitational field strength is the gravitational force exerted per unit mass at a point in the field

bull 119892 =119865

119898

bull Units N119896119892minus1

bull Field strength is a property of the field

bull It depends on a test mass

bull A test mass is small so its effects on the field can be ignored

Red shows higher ldquogrdquo

copycg

rah

amp

hys

ics

com

20

16

Field lines bull Field lines point in the direction a free body would begin to

accelerate if released

bull Density of field lines they are a measure of field strength which is equivalent to free fall acceleration at that point

bull 119892 =119865

119898=

119898119886

119898= 119886

bull All field lines come from infinity and end on masses

copycg

rah

amp

hys

ics

com

20

16

Universal law of gravitation

bull Every material particle in the Universe attracts every other material particle with a force that is directly proportional to the product of the masses of the particles and inversely proportional to the square of the distance between them

bull G= 667times 10minus11119873119898minus2119896119892minus2

copycg

rah

amp

hys

ics

com

20

16

Forces obey Newtonrsquos 3rd law bull Forces are equal and opposite

bull Mass is gravitational mass

bull 119877 ne distance between centre of masses but it is a force law between particles and not objects or masses

bull Newton deduced that spheres of mass follow the same law where the separation is between their centers

bull Example How fast does the apple drop

Assume apple weighs 1g and Earth 598 times 1024kg The radius of Earth is 64119909106m

bull 119892 =119865

119898=

119866119872119898

1198772119898=

119866119872

1198772=

667times10minus11times598times1024

64119909106 2

bull 119892 = 974119898119904minus2

bull This is the acceleration due to the gravitational field

copycg

rah

amp

hys

ics

com

20

16

ldquogrdquo has two different units bull F = ma where g = a

bull ldquogrdquo is N119896119892minus1 or m119904minus2

bull N119896119892minus1 is used if explicitly dealing with field strength 119892 =119865

119898

bull 119865119892 =119866119872119898

1198772 gravitational force

bull Remember gravitational field intensity near a point mass in N119896119892minus1

119892 =119865

119898=119866119872119898

1198772119898=119866119872

1198772

bull Law deals with point masses

bull Forces acting on masses are equal and opposite

bull Forces are always attractive

bull Forces are between all objects but only significant if objects involved are massive

copycg

rah

amp

hys

ics

com

20

16

Definitions

Force field

bull A region where a force acts

bull Strength of field varies with distance of central mass

Field theory

bull Original force at a distance without interaction

bull Field cannot directly be observed only measured by its effect on masses

bull Modern view quantum field theory

bull Force is transmitted between masses when exchanging ldquovirtualrdquo gravitons

bull Not observed yet

copycg

rah

amp

hys

ics

com

20

16

Representing gravitational field

bull It exerts forces at any point within the field

bull Must have strength and direction

bull Described by gravitational field strength ldquogrdquo

bull ldquogrdquo ne gravity

bull When masses are moved in a gravitational field their PE in the field changes

bull This is called gravitational potential

copycg

rah

amp

hys

ics

com

20

16

Gravitational field strength

bull Gravitational field strength is the gravitational force exerted per unit mass at a point in the field

bull 119892 =119865

119898

bull Units N119896119892minus1

bull Field strength is a property of the field

bull It depends on a test mass

bull A test mass is small so its effects on the field can be ignored

Red shows higher ldquogrdquo

copycg

rah

amp

hys

ics

com

20

16

Field lines bull Field lines point in the direction a free body would begin to

accelerate if released

bull Density of field lines they are a measure of field strength which is equivalent to free fall acceleration at that point

bull 119892 =119865

119898=

119898119886

119898= 119886

bull All field lines come from infinity and end on masses

copycg

rah

amp

hys

ics

com

20

16

Universal law of gravitation

bull Every material particle in the Universe attracts every other material particle with a force that is directly proportional to the product of the masses of the particles and inversely proportional to the square of the distance between them

bull G= 667times 10minus11119873119898minus2119896119892minus2

copycg

rah

amp

hys

ics

com

20

16

Forces obey Newtonrsquos 3rd law bull Forces are equal and opposite

bull Mass is gravitational mass

bull 119877 ne distance between centre of masses but it is a force law between particles and not objects or masses

bull Newton deduced that spheres of mass follow the same law where the separation is between their centers

bull Example How fast does the apple drop

Assume apple weighs 1g and Earth 598 times 1024kg The radius of Earth is 64119909106m

bull 119892 =119865

119898=

119866119872119898

1198772119898=

119866119872

1198772=

667times10minus11times598times1024

64119909106 2

bull 119892 = 974119898119904minus2

bull This is the acceleration due to the gravitational field

copycg

rah

amp

hys

ics

com

20

16

ldquogrdquo has two different units bull F = ma where g = a

bull ldquogrdquo is N119896119892minus1 or m119904minus2

bull N119896119892minus1 is used if explicitly dealing with field strength 119892 =119865

119898

bull 119865119892 =119866119872119898

1198772 gravitational force

bull Remember gravitational field intensity near a point mass in N119896119892minus1

119892 =119865

119898=119866119872119898

1198772119898=119866119872

1198772

bull Law deals with point masses

bull Forces acting on masses are equal and opposite

bull Forces are always attractive

bull Forces are between all objects but only significant if objects involved are massive

copycg

rah

amp

hys

ics

com

20

16

Representing gravitational field

bull It exerts forces at any point within the field

bull Must have strength and direction

bull Described by gravitational field strength ldquogrdquo

bull ldquogrdquo ne gravity

bull When masses are moved in a gravitational field their PE in the field changes

bull This is called gravitational potential

copycg

rah

amp

hys

ics

com

20

16

Gravitational field strength

bull Gravitational field strength is the gravitational force exerted per unit mass at a point in the field

bull 119892 =119865

119898

bull Units N119896119892minus1

bull Field strength is a property of the field

bull It depends on a test mass

bull A test mass is small so its effects on the field can be ignored

Red shows higher ldquogrdquo

copycg

rah

amp

hys

ics

com

20

16

Field lines bull Field lines point in the direction a free body would begin to

accelerate if released

bull Density of field lines they are a measure of field strength which is equivalent to free fall acceleration at that point

bull 119892 =119865

119898=

119898119886

119898= 119886

bull All field lines come from infinity and end on masses

copycg

rah

amp

hys

ics

com

20

16

Universal law of gravitation

bull Every material particle in the Universe attracts every other material particle with a force that is directly proportional to the product of the masses of the particles and inversely proportional to the square of the distance between them

bull G= 667times 10minus11119873119898minus2119896119892minus2

copycg

rah

amp

hys

ics

com

20

16

Forces obey Newtonrsquos 3rd law bull Forces are equal and opposite

bull Mass is gravitational mass

bull 119877 ne distance between centre of masses but it is a force law between particles and not objects or masses

bull Newton deduced that spheres of mass follow the same law where the separation is between their centers

bull Example How fast does the apple drop

Assume apple weighs 1g and Earth 598 times 1024kg The radius of Earth is 64119909106m

bull 119892 =119865

119898=

119866119872119898

1198772119898=

119866119872

1198772=

667times10minus11times598times1024

64119909106 2

bull 119892 = 974119898119904minus2

bull This is the acceleration due to the gravitational field

copycg

rah

amp

hys

ics

com

20

16

ldquogrdquo has two different units bull F = ma where g = a

bull ldquogrdquo is N119896119892minus1 or m119904minus2

bull N119896119892minus1 is used if explicitly dealing with field strength 119892 =119865

119898

bull 119865119892 =119866119872119898

1198772 gravitational force

bull Remember gravitational field intensity near a point mass in N119896119892minus1

119892 =119865

119898=119866119872119898

1198772119898=119866119872

1198772

bull Law deals with point masses

bull Forces acting on masses are equal and opposite

bull Forces are always attractive

bull Forces are between all objects but only significant if objects involved are massive

copycg

rah

amp

hys

ics

com

20

16

Gravitational field strength

bull Gravitational field strength is the gravitational force exerted per unit mass at a point in the field

bull 119892 =119865

119898

bull Units N119896119892minus1

bull Field strength is a property of the field

bull It depends on a test mass

bull A test mass is small so its effects on the field can be ignored

Red shows higher ldquogrdquo

copycg

rah

amp

hys

ics

com

20

16

Field lines bull Field lines point in the direction a free body would begin to

accelerate if released

bull Density of field lines they are a measure of field strength which is equivalent to free fall acceleration at that point

bull 119892 =119865

119898=

119898119886

119898= 119886

bull All field lines come from infinity and end on masses

copycg

rah

amp

hys

ics

com

20

16

Universal law of gravitation

bull Every material particle in the Universe attracts every other material particle with a force that is directly proportional to the product of the masses of the particles and inversely proportional to the square of the distance between them

bull G= 667times 10minus11119873119898minus2119896119892minus2

copycg

rah

amp

hys

ics

com

20

16

Forces obey Newtonrsquos 3rd law bull Forces are equal and opposite

bull Mass is gravitational mass

bull 119877 ne distance between centre of masses but it is a force law between particles and not objects or masses

bull Newton deduced that spheres of mass follow the same law where the separation is between their centers

bull Example How fast does the apple drop

Assume apple weighs 1g and Earth 598 times 1024kg The radius of Earth is 64119909106m

bull 119892 =119865

119898=

119866119872119898

1198772119898=

119866119872

1198772=

667times10minus11times598times1024

64119909106 2

bull 119892 = 974119898119904minus2

bull This is the acceleration due to the gravitational field

copycg

rah

amp

hys

ics

com

20

16

ldquogrdquo has two different units bull F = ma where g = a

bull ldquogrdquo is N119896119892minus1 or m119904minus2

bull N119896119892minus1 is used if explicitly dealing with field strength 119892 =119865

119898

bull 119865119892 =119866119872119898

1198772 gravitational force

bull Remember gravitational field intensity near a point mass in N119896119892minus1

119892 =119865

119898=119866119872119898

1198772119898=119866119872

1198772

bull Law deals with point masses

bull Forces acting on masses are equal and opposite

bull Forces are always attractive

bull Forces are between all objects but only significant if objects involved are massive

copycg

rah

amp

hys

ics

com

20

16

Field lines bull Field lines point in the direction a free body would begin to

accelerate if released

bull Density of field lines they are a measure of field strength which is equivalent to free fall acceleration at that point

bull 119892 =119865

119898=

119898119886

119898= 119886

bull All field lines come from infinity and end on masses

copycg

rah

amp

hys

ics

com

20

16

Universal law of gravitation

bull Every material particle in the Universe attracts every other material particle with a force that is directly proportional to the product of the masses of the particles and inversely proportional to the square of the distance between them

bull G= 667times 10minus11119873119898minus2119896119892minus2

copycg

rah

amp

hys

ics

com

20

16

Forces obey Newtonrsquos 3rd law bull Forces are equal and opposite

bull Mass is gravitational mass

bull 119877 ne distance between centre of masses but it is a force law between particles and not objects or masses

bull Newton deduced that spheres of mass follow the same law where the separation is between their centers

bull Example How fast does the apple drop

Assume apple weighs 1g and Earth 598 times 1024kg The radius of Earth is 64119909106m

bull 119892 =119865

119898=

119866119872119898

1198772119898=

119866119872

1198772=

667times10minus11times598times1024

64119909106 2

bull 119892 = 974119898119904minus2

bull This is the acceleration due to the gravitational field

copycg

rah

amp

hys

ics

com

20

16

ldquogrdquo has two different units bull F = ma where g = a

bull ldquogrdquo is N119896119892minus1 or m119904minus2

bull N119896119892minus1 is used if explicitly dealing with field strength 119892 =119865

119898

bull 119865119892 =119866119872119898

1198772 gravitational force

bull Remember gravitational field intensity near a point mass in N119896119892minus1

119892 =119865

119898=119866119872119898

1198772119898=119866119872

1198772

bull Law deals with point masses

bull Forces acting on masses are equal and opposite

bull Forces are always attractive

bull Forces are between all objects but only significant if objects involved are massive

copycg

rah

amp

hys

ics

com

20

16

Universal law of gravitation

bull Every material particle in the Universe attracts every other material particle with a force that is directly proportional to the product of the masses of the particles and inversely proportional to the square of the distance between them

bull G= 667times 10minus11119873119898minus2119896119892minus2

copycg

rah

amp

hys

ics

com

20

16

Forces obey Newtonrsquos 3rd law bull Forces are equal and opposite

bull Mass is gravitational mass

bull 119877 ne distance between centre of masses but it is a force law between particles and not objects or masses

bull Newton deduced that spheres of mass follow the same law where the separation is between their centers

bull Example How fast does the apple drop

Assume apple weighs 1g and Earth 598 times 1024kg The radius of Earth is 64119909106m

bull 119892 =119865

119898=

119866119872119898

1198772119898=

119866119872

1198772=

667times10minus11times598times1024

64119909106 2

bull 119892 = 974119898119904minus2

bull This is the acceleration due to the gravitational field

copycg

rah

amp

hys

ics

com

20

16

ldquogrdquo has two different units bull F = ma where g = a

bull ldquogrdquo is N119896119892minus1 or m119904minus2

bull N119896119892minus1 is used if explicitly dealing with field strength 119892 =119865

119898

bull 119865119892 =119866119872119898

1198772 gravitational force

bull Remember gravitational field intensity near a point mass in N119896119892minus1

119892 =119865

119898=119866119872119898

1198772119898=119866119872

1198772

bull Law deals with point masses

bull Forces acting on masses are equal and opposite

bull Forces are always attractive

bull Forces are between all objects but only significant if objects involved are massive

copycg

rah

amp

hys

ics

com

20

16

Forces obey Newtonrsquos 3rd law bull Forces are equal and opposite

bull Mass is gravitational mass

bull 119877 ne distance between centre of masses but it is a force law between particles and not objects or masses

bull Newton deduced that spheres of mass follow the same law where the separation is between their centers

bull Example How fast does the apple drop

Assume apple weighs 1g and Earth 598 times 1024kg The radius of Earth is 64119909106m

bull 119892 =119865

119898=

119866119872119898

1198772119898=

119866119872

1198772=

667times10minus11times598times1024

64119909106 2

bull 119892 = 974119898119904minus2

bull This is the acceleration due to the gravitational field

copycg

rah

amp

hys

ics

com

20

16

ldquogrdquo has two different units bull F = ma where g = a

bull ldquogrdquo is N119896119892minus1 or m119904minus2

bull N119896119892minus1 is used if explicitly dealing with field strength 119892 =119865

119898

bull 119865119892 =119866119872119898

1198772 gravitational force

bull Remember gravitational field intensity near a point mass in N119896119892minus1

119892 =119865

119898=119866119872119898

1198772119898=119866119872

1198772

bull Law deals with point masses

bull Forces acting on masses are equal and opposite

bull Forces are always attractive

bull Forces are between all objects but only significant if objects involved are massive

copycg

rah

amp

hys

ics

com

20

16

ldquogrdquo has two different units bull F = ma where g = a

bull ldquogrdquo is N119896119892minus1 or m119904minus2

bull N119896119892minus1 is used if explicitly dealing with field strength 119892 =119865

119898

bull 119865119892 =119866119872119898

1198772 gravitational force

bull Remember gravitational field intensity near a point mass in N119896119892minus1

119892 =119865

119898=119866119872119898

1198772119898=119866119872

1198772

bull Law deals with point masses

bull Forces acting on masses are equal and opposite

bull Forces are always attractive

bull Forces are between all objects but only significant if objects involved are massive

copycg

rah

amp

hys

ics

com

20

16