2. EXPECTATIONS:
Determine where gravity exists and what factors
affect the force of gravity.
Learn the difference between weight and mass.
Calculate weight.
Describe centripetal force and apply it
to Earth’s satellites.

3. GRAVITY 1. Gravity - the force of attraction between two
objects due to their mass.
2. Objects fall to earth because of the pull of
earth’s gravity. Galileo found all objects
fall towards the Earth with the same acceleration.
3. An object’s acceleration
near the surface of the earth is 9.8m/sec/sec.

4. 4. The acceleration due to gravity of an object in real
life is effected by air resistance.
-If there was no air, which would hit the ground first:
a feather or an elephant?

6. Notice the large and small rocks both have
the same acceleration!

7. -If you add air resistance, which would hit the
ground first: a feather or an elephant?

8. Notice the ball is
accelerating as it goes
down.

9. 5. Weight and mass are not the same thing.
Mass = a measure of the quantity of matter in
an object.
Weight= mass X acceleration due to gravity
(9.8 m/sec/sec)
*Notice that weight is just the unbalanced force
from Newton’s 2nd Law (F = m X a)

11. Find your weight on other worlds!

12. 6. Newton determined the Universal Law of
Gravitation.
a. Every object attracts every other object.
b.The force of gravity is directly proportional to the
product (multiplied) of the objects masses.
This means the larger the object(s), the more
gravitational force.
c. The force of gravity is inversely proportional to
the square of the distance between the two
objects. This means, the larger the distance
between the two objects, the less the
gravitational force.

14. 7. The Law of Universal Gravitation formula.

15. 8. Earth – Moon Interactions
The Earth’s gravitational pull on the moon is
always pulling the moon towards the Earth.
Why doesn’t it ever collide?
Newton reasoned that if the cannon projected
the cannon ball with exactly the right velocity,
the projectile would travel completely around the
Earth, always falling in the gravitational field but
never reaching the Earth, which is curving away
at the same rate that the projectile falls.
b. The moon is a just the right distance and
velocity that it is constantly in orbit.

16. Centripetal force is a center- directed force that continuously
changes the direction of an object
to make it move in a circle.
When you spin a bucket of water over your head
without spilling a drop, you are also applying a
centripetal force.
If you let go of the bucket, it will move in a
straight line.

17. What is exerting the
centripetal force in
these examples?

18. What is providing the
centripetal force here?

19. http://www. teachersdomain. org/resource/ess05. sci. ess. eiu
Video explaining why the moon does fall into the Earth.