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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
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
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
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
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amp
hys
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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
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