Topic # 5.5
GPS: 8b,c,d
Gravity, Weight
Date: _____/_____/_____
SPS8. Students will determine relationships among force, mass, and motion. b. Apply
Newton’s three laws to everyday situations by explaining the following: inertia,
relationship between force, mass and acceleration, equal and opposite forces c. Relate
falling objects to gravitational force. d. Explain the difference in mass and weight.
Part 1: Gravity: A Basic Force
 we have been learning about _______ and _______ that mainly occur _____ to
_____ or _____ to _____. Today we are learning about motion that occurs up and
down as a result of the force of ________.
 gravity = the _____________ force between any ____ objects.
 this force depends on:
gravitational = G  mass1  mass2
 the _____ of the two objects, and
force
distance2
 the _______ between the two objects
 the law of _________ ___________ shows this relationship.
 you will ____ have to calculate with this equation, but you need to _____ it.
 G = gravitational __________ = ______________ Nm2/kg2
 the ______ of gravity between most everyday objects is ______ _________
because the mass ___________ between the two objects is not _______
enough to ___________ to a noticeable force.
 for instance, let’s say we have two ___________,
each weighing _______ kg, standing ____ apart.
If we plugged in their masses and distance into the
equation above, we would get only about ____ N
of gravitational force between them.
 Why? Because “G” is really _______. 6.673 × 10-11 = _________________
 in order to ______ feel the force of gravity, you have to have _____ differences
between the ______ of your two objects AND a ____ distance between them.
 let’s say we have two objects that are VERY
different in mass: The ______ and an ______.
 Earth = ___________ kg, apple = _____ kg
 distance between them = _________ of Earth
 plugging these values into the equation above
would give a total _______ of about _____ N.
 that’s about ______ times the amount of gravitational
force that was experienced by the 2 elephants!
 _________ orbit the sun due to gravitational force. The _____ orbits the Earth for
the same reason. ALL objects are _______ gravitational forces on all other objects.
Part 2: Acceleration Due to Gravity
F = ma
 according to Newton’s ____ Law of Motion, F = ________
 when an object is ________, it falls to Earth due to the ___________ of gravity.
 so another way of writing F = ma is F = m___
Fgravity = mg
 the acceleration of gravity (g) is a _______ (it’s always the same)
 for example, the gravitational force on a _________ who’s mass is
g = 9.8 m/s2
___ kg would be:
 the acceleration of gravity is the ______ for all
g = 9.8 m/s2
objects, no matter what their _______ is.
 the two pictures to the right show objects in _____ _____.
____ ______ photography was used to take the pictures.
 notice how the _______ falls at the same ______ as the
apple. In a vacuum, there is no ____ __________ to
prevent the feather from falling more ________.
 also, notice how the objects are “________ up” as they
fall. What do we call this? __________________
Part 3: Weight vs. Mass
 even if you are not _______, the force of Earth’s gravity is still
pulling you ______________. The force of the _____ you are standing on pushes
___ with the same amount of force, so the net force on you is ______.
W = mg
 weight = the ______________ _____ exerted on an object.
 mass = a measure of the amount of _________ a substance contains
 mass and weight are _____ the same!!!
 the weight of an object ______ from one planet to another.
For instance, the gravitational force on the _____ (gmoon) is
______ m/s2.
 if you weigh ____ N (about ____ lbs) on Earth, you’d only
weigh _____ N on the moon (about ___ lbs)!
 would your mass change on the moon? _______
 “_________________” is a term to describe what
an object experiences when it seems to be
“________” relative to its _______________.
 objects on the ____ ______ seem to be floating,
but really, they are just falling towards the Earth
with the same ___________ as the shuttle itself.
Ex1: A textbook has a mass of 2.3 kg.
What is its weight in Newtons?
w=
m=
g=
SPS8. Students will determine relationships among force, mass, and motion. b. Apply
Newton’s three laws to everyday situations by explaining the following: inertia,
relationship between force, mass and acceleration, equal and opposite forces c. Relate
falling objects to gravitational force. d. Explain the difference in mass and weight.
Topic # 5.5
GPS: 8b,c,d
Gravity, Weight
Date: _____/_____/_____
SPS8. Students will determine relationships among force, mass, and motion. b. Apply
Newton’s three laws to everyday situations by explaining the following: inertia,
relationship between force, mass and acceleration, equal and opposite forces c. Relate
falling objects to gravitational force. d. Explain the difference in mass and weight.
Part 1: Gravity: A Basic Force
 we have been learning about forces and motion that mainly occur front to back or
side to side. Today we are learning about motion that occurs up and down as a
result of the force of gravity.
 gravity = the attractive force between any two objects.
 this force depends on:
gravitational = G  mass1  mass2
 the mass of the two objects, and
force
distance2
 the distance between the two objects
 the law of universal gravitation shows this relationship.
 you will not have to calculate with this equation, but you need to know it.
 G = gravitational constant = 6.673 × 10-11 Nm2/kg2
 the force of gravity between most everyday objects is barely noticeable
because the mass difference between the two objects is not large enough to
calculate to a noticeable force.
 for instance, let’s say we have two elephants, each
weighing 12,000 kg, standing 1 m apart. If we
plugged in their masses and distance into the
equation above, we would get only about 0.01 N
of gravitational force between them.
 Why? Because “G” is really small. 6.673 × 10-11 = 0.00000000006673
 in order to really feel the force of gravity, you have to have HUGE differences
between the masses of your two objects AND a short distance between them.
 let’s say we have two objects that are VERY
different in mass: The Earth and an apple.
 Earth = 5.974 × 1024 kg, apple = .25 kg
 distance between them = radius of Earth
 plugging these values into the equation above
would give a total force of about 1.0 N.
 that’s about 100 times the amount of gravitational force
that was experienced by the 2 elephants!
 planets orbit the sun due to gravitational force. The moon orbits the Earth for the
same reason. ALL objects are exerting gravitational forces on all other objects.
Part 2: Acceleration Due to Gravity
F = ma
 according to Newton’s 2nd Law of Motion, F = ma
 when an object is dropped, it falls to Earth due to the acceleration of gravity.
 so another way of writing F = ma is F = mg
Fgravity = mg
 the acceleration of gravity (g) is a constant (it’s always the same)
 for example, the gravitational force on a skydiver who’s mass is
g = 9.8 m/s2
60 kg would be:
F = mg = (60 kg)(9.8 m/s2) = 588 N
 the acceleration of gravity if the same for all
g = 9.8 m/s2
objects, no matter what their mass is.
 the two pictures to the right show objects in free fall.
Time lapse photography was used to take the pictures.
 notice how the feather falls at the same rate as the apple.
In a vacuum, there is no air resistance to prevent the
feather from falling more slowly.
 also, notice how the objects are “speeding up” as they
fall. What do we call this? Acceleration!!!
Part 3: Weight vs. Mass
 even if you are not falling, the force of Earth’s gravity is still
pulling you downwards. The force of the floor you are standing on pushes up with
the same amount of force, so the net force on you is zero.
W = mg
 weight = the gravitational force exerted on an object.
 mass = a measure of the amount of matter a substance contains
 mass and weight are NOT the same!!!
 the weight of an object varies from one planet to another.
For instance, the gravitational force on the moon (gmoon)
is 1.6 m/s2.
 if you weigh 700 N (about 160 lbs) on Earth, you’d only
weigh 119 N on the moon (about 26 lbs)!
 would your mass change on the moon? _______
 “weightlessness” is a term to describe what an
object experiences when it seems to be “floating”
relative to its surroundings.
 objects on the space shuttle seem to be floating,
but really, they are just falling towards the Earth
with the same acceleration as the shuttle itself.
Ex1: A textbook has a mass of 2.3 kg.
What is its weight in Newtons?
w=
m=
g=