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Title: Survey of the Universe Tom Burbine tburbine@mtholyoke.edu


1
Survey of the UniverseTom Burbinetburbine_at_mtho
lyoke.edu
2
Galileo Galilei (1564-1642)
  • He was able to figure out answers to these
    arguments
  • 1) Things in motion tend to remain in motion.
  • 2) He used a telescope to see sunspots on the Sun
    and features on the Moon.
  • 3) Galileo found that stars were more numerous
    and more distant than imagined

3
He also
  • He discovered the moons of Jupiter and saw that
    they were orbiting Jupiter
  • Io
  • Europa
  • Ganymede
  • Callisto
  • Proving that bodies could orbit other bodies
    besides the Earth

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Galileo also found that Venus orbited the Sun
6
Difference between mass and weight
  • Mass is the amount of matter in your body
  • Weight is the amount of force acting on your body
  • So on the Moon, you would have the same mass as
    on Earth but weigh less on the Moon since the
    Moon is less massive than Earth
  • Mass in metric system is usually measured in
    kilograms

7
Isaac Newton (1642-1727)
  • Supposedly saw an apple fall to the ground
  • He then understood that gravity was universal,
    meaning it affected both the planets and us on
    Earth
  • Came up with 3 Laws of Motion
  • Also came up with calculus

8
Force
  • Force anything that can cause a body to change
    velocity
  • Velocity a speed in a particular direction

9
Gravity
  • Gravity is a natural phenomenon by which objects
    with mass attract one another.

10
Newton
  • http//www.youtube.com/watch?v_q6CXni6yTE

11
Newtons 1st Law
  • In the absence of a net (overall) force acting
    upon it, an object moves with a constant velocity
  • An object at rest remains at rest
  • An object in motion tends to remain in motion
    unless a force is acting upon it

12
Why do things on Earth not remain in motion?
13
Why do things on Earth not remain in motion?
  • Friction

14
Objects in orbit
  • Because the planets are moving in elliptical
    orbits around the Sun and not straight lines,
    there must be a force acting on the planets
  • This force is gravity

15
Acceleration
  • Acceleration is when your velocity is changing
  • Velocity not changing, no acceleration

16
Acceleration
  • a ?v/?t
  • Car is travelling at 10 m/s
  • Increases its speed to 30 m/s over 5 seconds
  • a (30 m/s 10 m/s)/5 seconds
  • a 4 m/s2

17
Acceleration due to Earths gravity
  • g 9.8 m/s2
  • If something is dropped, it will gain 9.8 m/s in
    velocity for every second it falls

18
Newtons 2nd Law
  • Force mass x acceleration
  • Units of Force kg?m/s2 newton

19
Newton
  • A Newton is equal to the amount of force required
    to accelerate a mass of one kilogram at a rate of
    one meter per second per second

20
How much do you weigh?
  • So much do you weigh
  • Say your mass is 100 kg
  • F 100 kg x 9.8 m/s2
  • F 980 Newtons
  • 9.8 m/s2 is the acceleration of gravity on Earth
  • This is the acceleration due to the Earths
    gravitational field

21
Newtons 3rd Law
  • For any force, there is an equal and opposite
    reaction force
  • Gravity is holding you on the ground
  • The ground is also pushing back up on you with
    the same amount of force

22
http//www.vshiksha.com/system/files/u1/pslvc6-roc
ket.jpg
23
Newtons Universal Law of Gravitation
  • Every mass attracts every other mass through the
    force called gravity
  • Every point mass attracts every single other
    point mass by a force pointing along the line
    intersecting both points.
  • The force is directly proportional to the product
    of the two masses and inversely proportional to
    the square of the distance between the point
    masses

24
Formula
  • Newton came up with this formula
  • Force is proportional to M1 M2

  • d2
  • M1, M2 are the masses of the two objects
  • d is the distance between the objects

25
  • If you want to calculate actual forces
  • F G M1 M2
  • d2
  • M1, M2 are the masses of the two objects
  • d is the distance between the objects
  • G constant 6.67 x 10-11 m3/(kg?s2)

26
So what should you know about this formula
  • F G M1 M2
  • d2
  • The force of attraction between any two objects
    is directly proportional to the product of their
    masses
  • The force of attraction between two objects
    decreases with the square of the distance between
    their centers
  • G is a very small number

27
assume all mass is concentrated in the center of
a body
28
What is the attraction of two 100 kg people in
the same room?
  • F G M1 M2
  • d2
  • Say their masses are both 100 kg
  • Their distances are 10 meters apart
  • F 6.67 x 10-11 m3/(kg?s2) 100100 kg2/(1010
    m2)
  • F 6.67 x 10-9 N 0.0000000067 N
  • Remember the person weighs 980 N

29
  • F G M1 M2
  • d2
  • The value of G was determined by
  • Henry Cavendish between
  • 1797-1798
  • G 6.67 x 10-11 m3/(kg?s2)
  • http//blogs.howstuffworks.com/2009/04/13/diy-calc
    ulate-the-gravitational-constant-like-cavendish-di
    d/

http//www.makingthemodernworld.org.uk/learning_mo
dules/maths/06.TU.02/illustrations/06.IL.09.gif
30
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