Mass vs Weight
Matter = the substance that
all physical objects are
made of
Matter is anything that has
mass and takes up space
Mass = the amount of
matter in an object
Finding the mass is
equivalent to counting
the number of atoms
(amount of matter)
something is made of
We can’t really count
atoms, instead we
compare objects by
using a balance
If a bowling ball has a
mass of 1000g, that’s
like saying it has the
same number of atoms
as 1000g of water or
1000g of gold or 1000g
of chips!
Isaac Newton
1642 – 1727
Not only does each atom
have mass, it also has
inertia
Inertia = a
resistance to a
change in
motion
A bowling ball will stay in one place
forever, until some force pushes or
pulls it.
A moving bowling ball will
just keep going until some
force stops it
Would you rather have a catch with a
bowling ball or a soccer ball?
A bowling ball has more atoms
A bowling ball has more inertia
A bowling ball is harder to throw
and to catch
Isaac Newton
1642 – 1727
What strange force
makes an apple
(or anything else)
fall from a tree?
GRAVITY
Newton theorized that all
matter has gravity
GRAVITY
An invisible force that
attracts all matter to all
other matter
What determines the amount of
gravity?
What determines the amount of
gravity?
If every atom has gravity, then
more atoms means more gravity
mass = the amount of
atoms in an object
What determines the amount of
gravity?
Which has more mass, an apple or a chimp?
Which has more mass, the apple or the Earth?
Which has more gravity between them, an apple
and a chimp or the apple and the Earth?
What determines the amount of
gravity?
Which has more mass, the Earth or the Sun?
Which has more gravity between them, an apple
and the Earth or an apple and the sun?
The Sun obviously has more mass and more
gravity, then how can the Earth pull harder?
There must be more than just mass involved!
What determines the amount of
gravity?
Newton decided that the farther away you get,
the weaker gravity becomes.
What determines the
amount of gravity?
•Mass
•Distance
What determines the
amount of gravity?
Newton actually found a way to
quantify the amount of gravity
Notice you need the mass of BOTH objects
ALSO – it is the
distance between
objects, NOT the
distance from the
Earth
Notice it is distance SQUARED.
2x the distance = 4x weaker gravity
3x the distance = 9x weaker gravity
10x the distance = 100x weaker gravity
What would gravity be like on the moon?
Gravity depends on the
mass and the distance
between objects.
Say you weigh 120 lbs on
Earth, then travel to the
moon.
The Moon is approximately 1/6 of the mass of the
Earth. (Would your mass change?)
What would gravity be like on the moon?
1/6 the mass will mean
1/6 the gravity!!!!
Things weigh 6x less
and fall 6x slower!
The Moon is approximately 1/6 of the mass of the
Earth.
So what is the actual difference between
mass and weight?
MASS = the amount of atoms
Weight = the amount of gravity
On the moon
Mass is the same, weight 6x less
So what is the actual difference between
mass and weight?
Deep in a coal mine
Mass is the same, gravity is
slightly larger
Flying in an airplane
Mass is the same, gravity
is slightly weaker
Mars is about
80% the mass
of Earth.
What would
you weigh on
Mars?
Explain this !!!!
A spring scale is used to
measure weight
PAY ATTENTION to the pointer when you zero
the scale!
Universal Gravitational constant
6.67 x
-11
10
3
m
-1
kg
-2
s
OR
3
.0000000000667 m
kg
2
s