1. Gravity
I’m attracted
to you

2. 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

3. Gravitational field strengths
Earth’s moon, 1.6 N kg-1
Earth 9.8 N kg-1
On the surface of the sun N kg-1
Black holes , so big that even light can’t escape

4. 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
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 )

5. 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 )
Try using W = mg , can you account for the difference ?

6. Mass of Earth Equate F = mg with
Allows the mass of the earth to estimated
Try it

7. Mass/ distance /radius of other planets
Equate the gravitational force with the centripetal force ( AH Physics ) to find mass
Use triangulation to find distance

8. Radius of planets
If 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.

9. 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 )

10. Problems What is the problem with Newton’s Theory ?
Newton : Static Universe and
intervenes from time to time to maintain the equilibrium