gravity-100810205111-phpapp02.p PHYSICSpt

PHYSICS CONCEPTS

1. What goes up, must come
down.

2. At the end of the lesson, you will be able to:
a.) define gravity and its fundamental nature as
an attractive force between objects with mass,
b.) demonstrate awareness of the existence of
gravity by identifying examples of its effects in
everyday life, and
c.) solve problem involving gravity.

3. Gravity

4. Law of Universal Gravitation
•What Newton realized is now called the law
of universal gravitation.
•The law of universal gravitation states that
the force of gravity acts between all
objects in the universe.
•This means that any two objects in the
universe, without exception, attract each
other.
•You are attracted not only to Earth but also
to all the other objects around you.

6. Gravity is a force that acts between
any two masses.
Two factors affect the gravitational attraction
between objects: mass and distance.

7. What direction is Gravity?
Earth’s gravity acts downward toward
the center of the Earth.

8. A cool thing about gravity is
that it acts through objects.

9. Force = Mass x Acceleration
(aka: Newton’s 2
nd
Law of Motion)
•As the mass of a moving object decreases, so does the
pull of gravity; but the acceleration of the object is
greater.
•As the mass of the object increases, so does the pull
of gravity; but the acceleration is less.

10. WEIGHT: the gravitational force that Earth exerts on any
objects on or near its surface.
* Measured in Newtons (N)

W= mg
What is the weight of a mass of 800g?

17. SAMPLE PROBLEM in F = G (m1 m2)
d²
Question: Two spheres, one with a mass of 10 kg and the other with a
mass of 15 kg, are placed 1 meter apart. What is the gravitational
force between them?

18. Question: Two spheres, one with a mass of 10 kg and the other with a
mass of 15 kg, are placed 1 meter apart. What is the gravitational
force between them?
Given:
G= 6.674 x 10 ¹¹
⁻
m1= 10 kg
m2= 15 kg
F=?
F = G (m1 m2)
d²
F = (6.674 x 10 ¹¹ ) (10 kg * 15 kg)
⁻
1 m²
F = 1.0011 x 10 N
⁻⁸

21. SAMPLE PROBLEM in F= Gm
r²
Question: The mass of the Earth is 5.972 × 10² kg, and the
⁴
radius of the Earth is 6.371 × 10 m. What is the force of
⁶
gravity?

22. Question: The mass of the Earth is 5.972 × 10² kg, and the
⁴
radius of the Earth is 6.371 × 10 m. What is the force of
⁶
gravity?
G= 6.674×10 ¹¹
⁻
m= 5.972×10²kg
⁴
r²= 6.371×10m
⁶
F= Gm
r²
F = (6.674 × 10 ¹¹ ) (5.972 × 10² kg)
⁻ ⁴

(6.371 × 10 m)²
⁶
F ≈ 784 N

23. Free Fall
•When the only force
acting on an object is
gravity, the object is
said to be in free fall.
•An object in free fall
is accelerating.
•Do you know why?
•In free fall, the force
of gravity is an
unbalanced force,
which causes an object
to accelerate.

24. •While it may seem
hard to believe at
first, all objects in
free fall
accelerate at the
same rate
regardless of
their masses.
•The two falling
objects in the
figure on the right
demonstrate this
principle.

26. Example-1: Compute the height of the body if it has a mass of 2 Kg and touches the
ground after 5 seconds?
Given
Time t = 5 sec
Mass= 2Kg
We have to compute the height. So, we can apply the first equation as given above.

27. A ball is dropped from a height of 5 meters. How fast will it be
moving just before it hits the ground?
h = 5 m
g = 9.8 m/s²
 
v = ?
v²= 2gh
v² = 2( 9.8 m/s² ) (5 m)
v² = 9.9 m/s
So, the ball will be moving approximately 9.9 m/s just before it hits
the ground.

28. A rock is dropped from a cliff. How fast will it be falling
after 3 seconds?
Given:
g = 9.8 m/s²
t = 3 s
v = ?
v=gt
v = (9.8 m/s²) (3 s)
v = 29.4 m/s
So, after 3 seconds, the rock will be falling at a speed of
29.4 m/s.

29. Air Resistance
•Despite the fact that all objects are
supposed to fall at the same rate, you know
that this is not always the case.
•For example, an oak leaf flutters slowly to
the ground, while an acorn drops straight
down.
•Objects falling through air experience a
type of fluid friction called air resistance.

30. Air Resistance
Gravity causes objects to accelerate downward,
whereas air resistance acts in the opposite direction
and reduces acceleration.
Falling objects with a greater surface area experience
more air resistance.

31. •In a vacuum, where there is no
air, all objects fall with
exactly the same rate of
acceleration.
•Air resistance increases
with velocity.
•As a falling object
speeds up, the force of
air resistance becomes
greater and greater.

32. Projectile Motion
•Rather than dropping a ball straight down,
what happens if you throw it horizontally?
•An object that is thrown is called a
projectile.
•Will a projectile that is thrown horizontally
land on the ground at the same time as an
object that is dropped?