Weight and Mass

1
Weight and Mass

2
Weight

• Two definitions
• To a physicist weight is a force.
• You and me weight is our perception of a force
  acting on us - a reaction (Newtons third law
  again).

3
Our Perception
4
Weightlessness

• Einsteins gedanken experiment. (Dont try
  this at home!)
• Consider the Space Shuttle!

5
Feathers and Battleships

6
Determining the Properties of Planets Easy

• Distance
• Size
• Rotation rate

7
HarderAge and Weight
8
Hard

• Mass
• Age
• Composition and internal structure
• Beware the carnival huckster!

9
To Weigh the Planets

• See what gravitational influence they exert on
  nearby objects
• not how they respond to the gravity of another
  object.

10
For example

• Earth drop a stone and weigh the Earth.
• Mars, Jupiter watch the moons
• Venus, Mercury what can we do? (No moons!)
• Sun and stars?

11
Teeter-Totters
12
Dumbbells in Space

• Remember 3rd Law! - drop the Earth.
• Consider a teeter-totter.

13
The Balance Pointcenter of gravity
14
Wobbling Stars
15
Multiple-Planet Systems
16
Hundreds Now Known