Gravity: A Force of Attraction
Station 5
Gravity is a pulling force
It pulls things down
towards the earth
Things fall because of gravity
Things always fall down
What is Gravity?
• Gravity is a force of
attraction between two
objects.
• All objects with mass
have gravity.
• Gravity acts like a
magnet pulling objects
together.
What Does Gravity Do?
• The Earth has gravity.
• Earth’s gravity pulls
everything to the core
of the Earth.
• Trees, water, animals,
buildings, and the air
we breathe are all held
here by gravity.
What Does Gravity Do?
• All objects with mass
exert a pulling force on
each other.
• All of the planets, the
stars and the moons of
the universe have
gravity. Even our own
bodies have gravity!
Gravitational Forces We Notice:
• The sun (1.98892 x 1030 kg)
is the most massive object in
our solar system and exerts a
huge gravitational force.
• This is why all the planets
stay in orbit around the sun.
Gravitational Forces We Notice:
• The Earth (5.9742 x 1024 kg) is
so massive that its
gravitational force keeps us
from falling off the planet!
• Compared with all objects
around you, Earth has a huge
mass. Therefore, Earth’s
gravitational force is very large.
Size of Gravity
• Gravity is affected by the
distance and mass of the
objects.
• The Earth and the moon
have a stronger pull on
each other than the Earth
and Jupiter because the
Earth and moon are closer
to one another.
Gravitational force is strong when distance between
two objects is small. If the distance between two
objects increases, the gravitational force pulling
them together decreases rapidly.
Gravitational force is small between objects that
have small masses. Gravitational force is large when
the mass of one or both objects is large.
Size of Gravity
• We don't actually "feel"
gravity. We only feel the
effects if we are trying to
overcome it by jumping or
if we fall.
• You must apply forces to
overcome the Earth’s
gravitational force any
time you lift objects or
even parts of your body.
Mass and Weight
• Mass is the "stuff" that
matter is made of.
• We measure mass in
grams.
• People often confuse mass
with weight.
Mass and Weight
• Weight is actually the
result of gravity pulling on
the object. We measure
weight in Newtons.
• The closer to the center of
the Earth, the more pull,
the more you weigh.
Mass and Weight
Your mass would stay the
same if you could travel
from planet to planet.
Your weight would vary
depending on how the
gravity of that planet pulls
on you.
Moon
• Earth has a stronger pull
than the moon because it
is larger.
• There is more pull on our
bodies here on the Earth
than astronauts
experience on the moon.
Weight on the
moon is 1/6 the
weight on Earth
What if gravity
disappeared?
The Effects of Gravity on Matter
• Gravity is a force of attraction between objects that is
due to their masses. Gravity can change the motion of
an object by changing its speed, direction, or both.
• All matter has mass, and gravity is a result of mass.
Therefore, all matter is affected by gravity and all objects
experience an attraction toward all other objects.
• The mass of most objects is too small to cause a force
large enough to move objects toward each other.