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 Weight1. Weigh it!

2. Calculate it!

But how?

Like all forces, you can measure weight (force of gravity) with a spring scale!

Discovering the Relationship Between Mass and Weight

- OR –Why Pirates Have Pet Toucans

and Not Pet EmusArg?

A Sample Graph(Thanks to Jacob and Teddy)

The Importance of the Slope

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? Our calculated slopes

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 ComparisonMass Weight

Symbol m w or Fg

Unit kilogram (kg) Newton (N)

How to Determine

Usually measure

w = m∙g

OR

w = 9.8 ∙m

Constancy Object has same mass everywhere

Object’s weight depends on location (planet, etc.)

A Cheesy (but Effective) Video Comparison