GRAVITY

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GRAVITY AND NEWTONS LAWS OF MOTION
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Question????
Which object will land sooner if dropped at the
same time, a tennis ball or a bowling ball?
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Acceleration Due To Gravity
Objects fall to the ground at the same rate
because the acceleration due to gravity is the
same for all objects.
Bowling ball and tennis ball
The mass of an object does not affect the rate at
which it falls.
Example of acceleration due to gravity http//www.
regentsprep.org/Regents/physics/phys01/accgravi/in
dex.htm
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ACCELERATING AT A CONSTANT RATE
All objects accelerate toward Earth at a rate
of 9.8 m/s/s.
WHAT DOES THIS MEAN?
This means that for every second an object falls,
the objects downward velocity increases by 9.8
m/s.
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Acceleration Due To Gravity
Objects fall to the ground at the same rate
because the acceleration due to gravity is the
same for all objects.
The mass of an object does not affect the rate at
which it falls.
All objects accelerate toward Earth at a rate of
9.8 m/s/s.
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What happens when I drop a tennis ball and a
piece of paper??
Is there something else acting on the paper to
cause it to not fall like the tennis ball? What?
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DOES AIR RESISTANCE AFFECT FALLING OBJECTS?
Yes!!
THE FORCE OF GRAVITY PULLS OBJECTS DOWNWARD AS
THE FORCE OF AIR RESISTANCE PUSHES IT UPWARD.
FREE FALL- when an object is being pulled down by
gravity, but no other forces are acting on it.
Does free fall occur with air resistance?
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Example of acceleration due to gravity
http//www.youtube.com/watch?v5C5_dOEyAfk
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Gravity, Free Fall, and Air Resistance
Gravity - the force that pulls objects toward
one another. Free Fall when only gravity is
acting on an object. This is rare because of
air resistance. All objects free fall at a
rate of 9.8 m/s. A golf ball and basketball
will hit the ground at the same time. Air
Resistance type of fluid friction which
increases with the surface area of the object.
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NEWTONS LAWS OF MOTION
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• Newtons Laws of Motion

Brainpop
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NEWTONS FIRST LAW OF MOTION AKA LAW OF INERTIA
An object at rest remains at rest and an object
in motion remains in motion at constant speed and
in a straight line unless acted on by an
unbalanced force.
Examples
The man will remain in motion until a force stops
his movement.
A golf ball on a tee.
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NEWTONS FIRST LAW OF MOTION
Also called LAW OF INERTIA
Inertia is the tendency of all objects to resist
any change in motion.
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NEWTONS SECOND LAW OF MOTION
The acceleration of an object depends on the mass
of the object and amount of force applied.
FORCEMASS X ACCELERATION
Or aF/m
How does Newtons Second Law explain why the
shuttles acceleration increases during takeoff?
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• The greater mass or velocity an object has, the
  greater its inertia.
• You can test this the next time you're at the
  grocery store! It takes a strong push to get a
  loaded shopping cart moving, but once it gathers
  speed it keeps
  going, even if you
  let go of the handle.
  When you stop
  a moving cart full
  of groceries, it takes much more
  force to
  stop it than an empty cart.
• Why? (it has more mass).

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WHAT IS MOMENTUM?
MOMENTUM is a property of a moving object that
depends on the objects mass and velocity.
Momentummass x velocity
THE MORE MOMENTUM AN OBJECT HAS, THE HARDER IT IS
TO STOP THE OBJECT OR CHANGE ITS DIRECTION.
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NEWTONS THIRD LAW OF MOTION
For every action there is an equal and opposite
reaction.
FORCES ALWAYS ACT IN PAIRS.
The action force is the swimmers hand and feet
pushing the water.
The reaction force is the water pushing on the
swimmers hands and feet.
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• According to Newton, whenever objects A and B
  interact with each other, they exert forces upon
  each other.
• When you sit in your chair, your body exerts a
  downward force on the chair and the chair exerts
  an upward force on your body.

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• Flying gracefully through the air, birds depend
  on Newtons third law of motion. As the birds
  push down on the air with their wings, the air
  pushes their wings up and gives them lift.

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MORE EXAMPLES OF ACTION AND REACTION FORCE PAIRS
The rabbits legs exert a force on Earth. Earth
exerts an equal force on the rabbits legs,
causing the rabbit to accelerate upward.
The shuttles thrusters push the exhaust gases
downward as the gases push the shuttle upward
with an equal force.
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LETS PRACTICE
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Explain Newtons First Law of Motion using this
picture.
A plane will not soar in the air unless it is
pushed by the exhaust from its jet engines.
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Newtons Second Law of Motion

• - Which would you have to apply a greater
• force to stop and go?
• - Which would you rather buy gas for?
• Which would you rather be driving in a
• head-on collision?

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NEWTONS THIRD LAW OF MOTION
LIST and DESCRIBE the action and reaction forces
in the following picture.
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