Download Gravity: a force of attraction between objects that is due to their mass

Target Thursday January 3, 2013
1.What is gravity?
2.How do you know it is there?
3.What causes gravity?
4.Name 3 things that are in
motion in this room right
now
Gravity: a force of attraction between
objects that is due to their mass
-All matter has mass
-All matter experiences gravity
The earth’s mass is large, therefore its
gravitational pull is large
British scientist Sir Isaac Newton
developed the “Law of Universal
Gravitation”
Gravity
What is Gravity?
• Gravity=FORCE!
• Gravity is a force of attraction.
• Gravity PULLS.
Matter & Gravity Facts
•
All matter has mass.
•
All matter experiences gravity.
•
All objects experience a gravitational
attraction toward each other.
Law of universal gravitation
• All objects in the universe attract each other
through gravitational force.
• The size of the
force depends
on mass and
distance.
Gravity depends on……
Mass
&
Distance
Law of Universal Gravitation Part 1:
Gravitational force increases as mass
increases
Gravity and Mass
Greater mass=greater gravitational pull.
Earth’s gravitational force is due to it’s
enormous mass.
Law of Universal Gravitation Part 2:
Gravitational force decreases as distance
increases
Gravity and Distance
Closer together=greater gravitational pull.
Which ones have more
gravitational pull?
Vs.
Vs.
Which ones have more
gravitational pull?
Vs.
Vs.
Now which ones?
Vs.
Vs.
Vs.
Vs.
Mass
• Amount of matter in an
object.
• Does not change with
location.
• Unit=grams
Weight
• Measure of the gravitational
force exerted on an object.
• Changes with location.
• Unit=Newtons
• A newton is the amount of force
it takes to accelerate 1 km of
mass 1 m/s
Force • a push or pull
• The
combination of
all forces acting
on an object is
the net force.
Balanced Force
• Two or more forces
exerted on an object
are balanced if their
effects cancel each
other and do not
cause a change in the
object’s motion.
• The net force is zero.
Unbalanced Force
• Occurs when the forces acting on the
object changes the object’s motion.
• The net force is NOT zero.
Target 1-14-14
1. What determines the gravitational force of an
individual object?
2. What would cause the force of gravity to be
greater between two objects if their mass stays
constant?
3. Why would you weigh less on the moon?
4. What two different instruments measure mass
and weight?
BRAINPOP
• http://www.brainpop.com/science/motionsfo
rcesandtime/gravity/
Friction -
• is a force that resists the sliding
between two touching surfaces.
• Friction is an opposing force
• Friction will always slow a moving
object.
Types of Friction
• Static friction causes surfaces to stick together.
It keeps an object at rest.
• Sliding friction slows down an object that
slides.
• Rolling friction is needed to make a wheel
turn.
• Fluid friction is air and/or water resistance.
INERTIA
• The tendency of an object to
remain at a constant speed
unless another force acts
upon it.
• If it is moving at a certain
speed it will stay at that
speed unless a force acts on
it.
• If it is still, then it will stay
still unless a force acts on it
NEWTON’s LAWS of MOTION
Newton’s 1st law sometimes called
“Law of Inertia”
Inertia: the tendency of all objects to
resist any change in motion
Newton’s 2nd Law:
The acceleration of an object depends
on the mass and the amount of force
Force = mass x acceleration
Newton’s
rd
3
Law:
When one object exerts a force on a
second object, the second object
exerts an equal and opposite force on
the first.
Objects in motion have
momentum because they have
mass. Momentum is conserved.
Gravity and Motion
Acceleration due to gravity
• Rate at which
velocity changes
because of the
pull of gravity.
• Earth=
9.8 m/s/s
Acceleration due to gravity
(g)
Gravity & Acceleration due to
gravity
All objects fall at the same rate because the
acceleration due to gravity is the same for all
objects.
• All objects accelerate toward Earth at 9.8
m/s/s
Air resistance,
a type of friction slows
down acceleration.
Air resistance is the force of friction
and the opposing force created by
going through the air.
Terminal velocity
• When an object falls at a constant velocity
because the air resistance force matches the
force of gravity.
• Net force=0
Would a parachute work on the
moon?
No air resistance, so no
.
Target 1-8-13
1.
2.
3.
4.
5.
What is acceleration due to gravity?
What causes terminal velocity?
What is terminal velocity?
What is inertia?
What is momentum?
Brainpop
• http://www.brainpop.com/science/motionsfo
rcesandtime/newtonslawsofmotion/
Free Fall
Free fall- when gravity is the
only force acting on an object
(free fall acceleration is directed
toward center of earth)
The acceleration of gravity (g)
for objects in free fall at the
earth's surface is 9.8 m/s2.
Galileo found that all things
fall at the same rate in the
absence of air resistance,
regardless of their mass
Orbiting objects are in free fall.
So if all objects experience gravity, then
can something ever be weightless?
No. When an object is “weightless” it is
really falling and hasn’t hit an object yet.
Free Fall
The rate of falling
increases by 9.8 m/s
every second.
Height = ½ gt2
For example:
½ (9.8 )12 = 4.9 m
½(9.8)22 = 19.6 m
½ (9.8)32 = 44.1 m
½ (9.8)42 = 78.4 m
Air Resistance
• In air…
– A stone falls
faster than a
feather
• Air resistance
affects stone
less
• In a vacuum
– A stone and a
feather will fall at
the same speed.
Free Fall
A ball
thrown
horizontally
will fall at
the same
rate as a ball
dropped
directly.
Free Fall
A ball thrown into the air
will slow down, stop, and
then begin to fall with the
acceleration due to
gravity. When it passes
the thrower, it will be
traveling at the same rate
at which it was thrown.
Projectile motion-curved path an
object takes when thrown near the
surface of the Earth.
2 parts of projectile motion:
Horizontal Motion
• Force of throw.
• Across
Vertical Motion
• Gravity pulling downward.
• Down
How does projectile motion
occur?
1) Which object will hit the ground first: an
apple or a feather?
Earth: The apple will not experience air
resistance like the feather, so the apple will fall
first.
Moon: They will both hit the ground at the
same time because there is no air resistance.
2) Why is the Earth round?
All the mass is pulled in
because of gravity.
3) This drawing shows an enlarged person
holding a rock. If he threw the rock slightly to
his right, what path would the rock take? Show
what happens to the rock by drawing a line showing the
complete path of the rock, from the person's hand to where it
finally stops.
Projectile Motion:
4) With enough force, would it be possible for
the rock never to hit the Earth?
Could be thrown into orbit around the Earth.
5) What weighs more: a pound of feathers or a
pound of bricks?
They each weigh the same. The Earth’s gravity
pulls on the objects the same.
6) Is gravity a pull or a push?
Pull.
7) True or False Weightlessness is not because
one is in space: it’s because one is falling!
Space has gravity just like everywhere else,
just no fixed objects to hold against to keep
from falling
True
8) True or False Everything that has mass has a
gravitational pull.
True
9) True or False Astronauts on the Moon were
not weightless! The Moon has gravity much
like the Earth. But since the Moon is less
massive, the gravitational pull is smaller. The
astronauts were pulled to the Moon with
about 1/6th the force of gravity back here on
Earth.
True
Galileo and Pisa
• http://www.youtube.com/watch?v=_KvU5tjNCY
• http://www.youtube.com/watch?v=03SPBXAL
JZI&feature=related
Projectile Motion
•An object thrown upward at an angle to the
ground follows a curved path called a
parabola.
• combines vertical and horizontal motion
•Orbiting objects- forward motion combines
with free fall and object follows a curved path
Free Fall Review
• Dropping something from a resting position
(gains speed as it falls so it accelerates)
• Gravity pulls objects down (air resistance can
affect how fast) (no air resistance- in a
vacuum)
• When gravity is the only thing that affects
falling object → FREE FALL
• Acceleration due to gravity is 9.8 m/s2
-TAKE A QUIZ FROM
THE BACK DESK
-YOU HAVE 10
MINUTES TO
COMPLETE THIS QUIZ
Illustrated Dictionary
For each term, write the word, the definition,
and give an illustration with color
Put your name in the box with Momentum
-Newton’s First Law
-Newton’s Second Law
-Newton’s Third Law
-momentum
-projectile motion
-free fall
-terminal velocity
-air resistance
Target 1-14-13
1. Do Newton’s Laws work in
space?
2. Why do astronaut’s have to
exercise while in space?
3. Why do astronauts get taller
while in space?
Target 1-16-13
• Read “Determining Net Force” on
pages 125-126
• Read “Balanced and Unbalanced
forces” on pages 126-127.
• Answer questions 2-5 on page
127
Force Problems
• There is a box sitting on the floor. Gravity
is pulling down on the box with 9.8 N of
force. The ground is applying the normal
force to the box at 9.8N. One man is
pushing the box to the left with 25N of
force and his friend is playing a joke on
him by pushing the box with 20N of force
to the right. What is the Net force on the
box? Is this balanced or unbalanced
force? Diagram the forces on the box.
Force Problems
• A plane is flying through the air. Gravity is
pulling down on the plane with a force of 9.8N.
The Lift created by the plane’s wings is pulling up
on the plane with a force of 9.8N. The force of
friction is pulling back on the plane with a force
of 10N. The thrust of the engines is propelling
the plane forward with a force of 10N. What is
the net force on the plane? Is this balanced or
unbalanced? Diagram the forces on the plane.
Target 1-22-13
Write one paragraph consisting
of 6-8 sentences describing
one of Newton’s Laws. Be
sure and give at least one
descriptive example.
Writing Topic
Writing Situation
The Earth, the moon, and Jupiter all have different
masses; therefore they have different gravitational
pulls.
Directions for Writing
Write an essay comparing and contrasting your life on
Earth with the Moon and Jupiter. Remember that
the Moon has 1/6th the gravity of Earth and Jupiter
has 2.5 times the Earth's gravity. In your answer
include specific examples about reduced and
increased gravity. What are some of the
adjustments you would need to make?
Friday January 18, 2013
•Take a Quiz from the
basket on the back desk
•You have 10 minutes to
complete the quiz