The Difference
between
Mass & Weight
That’s heavy man.
Heavy…
What we learned last
time:
Gravity is dependant upon the mass of two
objects and the distance between them.
– If mass increases – Force of Gravity increases
– If distance increases – Force of Gravity decreases.
Jupiter has more mass than Earth;
Therefore it has more gravity
The satellite is farther from the center of Earth than we are;
Therefore the planet is not pulling as hard on the satellite
as the person standing on the surface!
What is Weight?
• Definition: Weight is a measurement of how
strongly gravity pulls on a mass.
• Weight is completely dependent on the amount
of gravity there is.
• It the result of the force of gravity!!!
• Without gravity there is NO WEIGHT (the
ultimate diet plan!!!)
Amount of Mass & Gravity
= Weight
• If you add more mass – you’ve increased
the attractive force between you and the
The Earth
earth
must really
• Therefore you “weigh” more!
like me!
Gravity, Distance and Weight:
• If I leave the earth and head to outer space, I
am farther away from the gravity source.
• Therefore, you weigh less.
Dude! I
CAN
FLOAT
AROUND!
Mass ≠ Weight
• Mass and Weight are NOT the same thing!
• Mass: Amount of matter an object contains
– Has inertia (resistance to a push/pull)
• Weight (Force):
– Dependant upon Gravity (mass is not)
• Attraction between two objects
• Can change if the objects change distance or
mass
Weight really is a measurement of the gravitational
attraction
between
you and =
theWeight
earth.
Mass
and
Gravity
Remember – Weight is a force measurement
When gravity pulls on your mass,
the resulting force is called “weight”!
Source of Gravity
Small mass = less pull = less weight
Source of Gravity
Large mass = more pull = more weight
Compare: Mass vs. Weight
on different planets:
Same person on
Jupiter is 354.6 lbs!!!
Person on Earth
is 150 lbs!
Why is this true? What is different
between Jupiter and Earth?
Jupiter has more mass than the Earth
Therefore it has more gravity! Your same
mass would weigh more on Jupiter than on Earth!
Q: Did the person’s MASS (amount
of matter that makes them
up) ever change?
Q: How does gravity
accelerate an object?
How objects fall as a result of gravity was a matter of debate for scientific
thinkers as far back as ancient times!
A “philosopher” named Aristotle felt that heavier objects
(greater weight) would fall faster than lighter objects
when pulled by gravity… This idea was accepted for 100’s of years!
After many years (during the renaissance) a scientist
To try and prove
idea, had
he took
cannonidea:
balls to the
namedhis
Galileo
a different
So what happened?
top of the leaning tower of Pisa…
Well, let’s go see for
ourselves!
He felt
that
objectsthem!!!
would fall at the same rate
And
then
heall
dropped
no matter what the mass or weight was…
Test of Gravity
• Which one fell faster – the heavier
one or the lighter one?
• Galileo found that no matter how
large or small, the objects fell at
the same Velocity.
• So at what rate do objects
accelerate due to Earth’s gravity?
Acceleration Rate of the
Earth
What is the acceleration of this interval?
1sec – 9.8m @ 9.8 m/s
What is the acceleration of this interval?
2sec – 19.6m @ 19.6 m/s
What is the acceleration of this interval?
3sec – 44.1m @ 29.4 m/s
•Gravity’s Acceleration on the Earth = 9.8 m/s2
Wait a second!
We already talked about how leaves and feathers
fall very slowly and even changes directions
So what makes the leaf and feather fall
differently than a cannon ball?
So will feathers and leaves always
fall slower than cannon balls?
Q: So what if
we got rid of
all the air?
Galileo Experiment – Apollo 15
Hammer & Feather Experiment
Google Video
So how do we solve for
weight?
Force = Mass x Acceleration
[m]
Force [ N ]  mass [kg]  Acceleration rate of gravity (9.8 2 )
[s ]
[kg m]
N
2
[s ]
Acceleration Rate of Earth’s
Gravitational Pull
Weight = Mass x Gravity Acceleration
• Compare your weight on Earth to what is
would be on the Moon:
• Discuss: Why does your weight change?
• Discuss: Does your mass change as well?
Class Activity
Gravity and Weight Lab