Transcript 4.1 Gravity - Teacher Pages

Integrated Science
Unit 1, Chapter 3
Bellringer:
What problems skydivers
might encounter if they tried
to skydive on the moon?
4.1 Gravity

What is gravity?
— Gravity is a force.
— Gravity depends on mass.
— Gravity accelerates objects.
— Why is the total force exerted
by the bag of flour less on
the moon?
• Gravity creates an attractive force
between all objects that have mass.
Unit
4.1 Gravity
 If
you were on Mars, your
force/mass balance would
have to be adjusted.
 The
planet is smaller than
Earth and therefore Mars’s
gravity is weaker.
3.2 Weight
Weight force (N)
Fw = mg
gravity (9.8 m/sec2)
mass (kg)
3.2 Weight and Galileo
A
legend has it that,
around 1587, Galileo
dropped two balls from
the Leaning Tower of
Pisa to see which would
fall faster.
4.1 Gravity
 There
is even a
gravitational force
between you and a book.
 You
don’t notice gravity
between ordinary objects
because it takes a huge
amount of mass to
create a force big
enough to feel.
4.1 Gravity
 The
gravitational force
between you and Earth is
much stronger than
between you and your
book.
3.2 Newton's Law of Universal
Gravitation
 Newton’s
law of universal gravitation says the
strength of the force depends on mass and
distance.
 If
two objects are the same mass they have the
pull on each other with the same amount of force
(Fg).
4.1 Law of gravitation
If one object doubles in mass, then the
gravitational force doubles.
4.1 Law of gravitation
 If
both objects double in mass, then the
force doubles twice, becoming four times as
strong.
4.1 Weightlessness

The astronauts in the space shuttle are not far
enough away to escape Earth’s gravity.

How do they float around with no apparent
weight?

The answer is that they are actually falling around
the Earth in their orbit.
4.1 Orbital motion
•
An orbit is the circular (or
elliptical) path an object
takes around a gravity
source, such as a planet or
star.
4.1 How an Orbit Is Formed
4.1 The Earth and Moon

The Moon is much smaller than Earth.

Because the Moon has much less
mass, its surface gravity is about 1/6 as
strong as the gravity on Earth.

Gravity provides unbalanced force that
cause objects to move in a circular
motion

The unbalanced force that causes
objects to move in a circular path called
a centripetal force.
Projectile Motion
 Any
object that is
moving through the air
affected only by gravity
is called a projectile.
 Projectile
motion has
two components –
horizontal (parallel to
the ground) and vertical
motion (perpendicular
to the ground).