Mass vs. Weight
Definitions
Mass – Amount of stuff (matter) in an
object
Weight – Force exerted on an object
because of a planet’s gravity
Related, but not the same!
Mass ≠ Weight!
How to Find Mass
Two types of mass!
• Gravitational Mass
2. Inertial Mass
A Video
How to Find Weight
1. Weigh it!
Like all forces, you can measure weight
(force of gravity) with a spring scale!
2. Calculate it!
But how?
Discovering the Relationship
Between Mass and Weight
- OR –
Why Pirates Have Pet Toucans
and Not Pet Emus
Arg?
A Sample Graph
(Thanks to Jacob and Teddy)
How Many Newtons?
14
12
Force in Newtons
10
y = 10.047x + 0.055
R² = 0.9981
8
6
4
2
0
0
0.2
0.4
Mass In Kg0.6
0.8
1
1.2
1.4
The Importance of the Slope
How Many Newtons?
14
y = 10.047x + 0.055
R² = 0.9981
12
Force in Newtons
Tells you how
much the
weight (Fg)
varies with
mass: If you
increase the
mass by 1 kg,
how much do
you increase
the weight by?
10
8
6
4
2
0
0
0.2
0.4
0.6
Mass In Kg
0.8
Our calculated slopes
1
1.2
1.4
Experimental Result
g = 9.81 N/kg
To calculate the weight, w, of an object of
mass m:
w = m∙g = 9.81 ∙ m
Example Calculations
1. What’s the weight of a 1.2 kg toucan?
w = mg = (1.2 kg)(9.81 N/kg) = 11.7 N
2. What’s the weight of a 97 kg emu?
w = mg = (97 kg)(9.81 N/kg) = 952 N
Weight Varies, Mass Does Not
If you move to a different location, the
amount of stuff in you doesn’t change, so
your mass is always the same.
BUT the force of gravity may be different,
causing your weight to be different.
Various Values of g and Effect on
Weight
Weight on Earth
Weight on other Planets
A Side-by-Side Comparison
Mass
Symbol
Unit
How to
Determine
m
kilogram (kg)
Usually
measure
Constancy
Object has
same mass
everywhere
Weight
w or Fg
Newton (N)
w = m∙g
OR
w = 9.8 ∙m
Object’s weight
depends on
location
(planet, etc.)
A Cheesy (but Effective) Video
Comparison