I’m attracted to you Gravity. Mass and Weight Mass is a measure of a body’s INERTIA Units are...
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Transcript of I’m attracted to you Gravity. Mass and Weight Mass is a measure of a body’s INERTIA Units are...
I’m attracted to you
Gravity
Mass and Weight
• Mass is a measure of a body’s INERTIA
• Units are kg, scalar
• Weight is the gravitational force acting on an object
• Units are N, vector• Gravitational field strength, g, is the
weight per unit mass, Nkg-1
Gravitational field strengths
• Earth’s moon, 1.6 N kg-1
• Earth 9.8 N kg-1
• On the surface of the sun 273.7 N kg-1
• Black holes , so big that even light can’t escape
Newton• The bigger the mass the bigger the force
of attraction• The further away from the planet / moon /
star the smaller the force of attraction
2
21
r
mmGF
F = force of attraction
G = Universal Gravitational constant
= 6.67x10-11Nm2kg-2
m1 = mass m2 = mass 2
r = distance between two masses ( for planets and so on we assume this is the distance from centre to centre )
Newton’s Law of Gravity
• Mass of earth = 6.0x1024 kg• Radius of earth = 6.4x106 m• Calculate the force acting on you ( assume all the
mass is concentrated at the centre of earth )
2
21
r
mmGF
N
x
xxxx
1.762
104.6
78100.61067.626
2411
Try using W = mg , can you account for the difference ?
Mass of Earth
• Equate F = mg with
2
21
r
mmGF
Allows the mass of the earth to estimated
Try it
gr
Gm
mgr
mGmF
21
221
kgx
x
xxm
G
gr
24
11
262
1002.6
1067.6
8.9104.6
Mass/ distance /radius of other planets
• Equate the gravitational force with the centripetal force ( AH Physics ) to find mass
• Use triangulation to find distance
Radius of planetsIf you know how far away a planet is from you, you can determine its linear diameter, D.
D = 2Π × (distance to the planet) × (the planet's angular size in degrees)/360° )
This technique is used to find the actual diameters of other objects as well, like moons, star clusters, and even entire galaxies.
Slingshot Effect
Think of the comet gaining some momentum as it approaches the planet which of course loses some momentum( it’s orbit speed will decrease slightly )
Problems
What is the problem with Newton’s Theory ?
2
21
r
mmGF
Newton : Static Universe and
intervenes from time to time to maintain the equilibrium