Download The Nature of Force and Motion Notes

Chapter 4: The Nature of Force and Motion Notes-pages 116- 121
What is a Force?
A. A _________________ is a push or a pull.
 When one object pushes or pulls another object, the ___________________
object is exerting a force on the _________________ object.
 You exert a ________________ on a pencil when you write, on a book when
you lift it, and on a doorknob when you pull on it.
 Forces like ____________________ & _____________, are described not only by
how strong they are, but also by the __________________ in which they act.
B. When _____________ forces act in the same direction, you ____________ them
together.
 The arrow or vector points in the ________________ of a force.
 The width of each arrow tells you the ______________ of a force. A
wider arrow shows a __________________ force.
 Two forces can combine so that they __________ together (top), or
_______________from each other (center). They can also
_______________ each other out (bottom).
 When forces act in _______________ directions, they also add
together.
 If one force is _________________ than the other force, the overall
force is in the _____________________of the greater force.
C. The overall force on an object after all the forces acting on it are added
together is called the ______________________. Forces give ________________ to
an object.
Forces and Motion
A. When a net force acts on an object, the forces are ___________________.
 ____________________ forces can cause an object to start ________________,
stop __________________, or change ____________________.
 Unbalanced forces acting on an object will change the object’s
_____________________ or cause an object to _______________________.
 For example, if two unequal ___________________ acting in opposite
directions are applied to a box, the box will accelerate in the
__________________ of the greater force.
B. Equal forces acting on one object in opposite directions are called
___________________ forces.
 One force is exactly ________________ by one or more other forces.
 Balanced forces acting on an object will ________ change the object’s
motion. When you add equal forces exerted in opposite directions, the
______________________ is zero.
Newton’s First Law of Motion
A. The ancient Greeks observed that objects have natural _________________.
 A rock ______________to the ground.
 A puff of smoke ________________ into the air.
 Once an object is in its natural resting place, it ______________ move by itself.
B. In the early 1600s, the Italian astronomer Galileo suggested that once an
object is in _____________, no _____________ or ___________ is needed to keep it
__________.
C. Force is needed only to _____________ the motion of an object. However,
whether it is moving or at rest, every object _________________ any change to
its motion. This resistance is called ________________.
D. ______________________is the tendency of an object to resist change in its
motion.
 A hockey puck that rides on a cushion of air in an “air-hockey” game glides
along quite freely once you push it.
 A tennis ball flies through the air once you hit it with a racket. In both cases,
the object continues to move even after you remove the force.
E. The English mathematician, Sir Isaac Newton discovered the three basic
____________________________________ in the late 1600s.
 Newton’s ________________ law of motion states that an object at
______________ will remain at _______________and an object that is
_________________ at constant velocity will continue __________________ at
constant velocity unless acted upon by an ________________________ force.
 An object will not start moving unless a __________ acts on it. An object will
not ________________ moving unless a force acts on it. An object will not
change ________________ unless a force acts on it. An object will not
change ________________unless a force acts on it.
 Newton’s first law of motion is also called the __________________________.
 Newton was the first scientist to use the term inertia to describe the
tendency of objects to remain in ________ or _____________at rest. Inertia
comes from the Latin word iners, which means “______________.”
EXAMPLE:
 If you are in a car that stops suddenly, _______________ causes you to
continue moving forward. Crash-test dummies don’t stop when the car
does. A _________ is required to change their motion. That force is exerted
by the safety belt.
Mass and Inertia
A. ____________ is the amount of matter in an object. (unit of mass is kg)
B. _________________ is the amount of space an object occupies.
C. The object with the _______________ mass has the greater ______________.
D. The amount of inertia an object has depends on its ___________. A car’s
mass is greater than the bicycle’s, so the car’s inertia is greater.
E. Mass can also be defined as a measure of the ____________ of an object.
Page 125 Force = _____________ X _________________
Force is measured in _________________. (N)
Chapter 4.3 Friction and Gravity Notes-pages 127-133
I.
Forces and Motion
A. According to Newton’s first law of motion, a book’s motion changes only if an ________________
acts on it. A force should not be necessary to keep the book moving at a __________________.
B. When the book slides, the force of _____________ causes it to slow to a stop. When the book falls,
the force of the _______________causes it to accelerate downward. In this section you will learn
that these two forces affect nearly all _________________.
II. Friction
A. When you push a book across a table, the _____________ of the book rubs against the
____________ of the table.
B. The force that one surface exerts on another when the two rub against each other is called _______________.
III. The Nature of Friction
A. ______________________acts in a direction _____________ to the object’s direction of motion.
Without __________________, the object would continue to move at constant speed forever.
Eventually friction will cause an object to come to a ________________.
B. The strength of the force of friction depends on the ________________ of surfaces involved and
how hard the surfaces _____________________________.
C. _________________________ produce greater friction than smooth surfaces. The skiers in the
photo get a fast ride because there is ______________ friction between their skis and the snow.
D. The force of friction also ________________ if the surfaces push harder against each other.
IV. Is Friction Useful?
A. You are able to walk because ________________ acts between the soles of your shoes and the
_______________. Without friction your shoes would only _____________ across the floor, and you
would never move _______________.
B. An automobile moves because of friction between its ______________ and the _________.
V. Controlling Friction
A. When solid surfaces slide over each other, the kind of friction that occurs is called __________________.
B. When an object rolls over a surface, the kind of friction that occurs is ____________________. The force
needed to overcome _______________ friction is much less than the force needed to overcome
________________ friction. ________________________ are one way of ____________________ friction
between two surfaces.
C. The friction that occurs when an object moves through a fluid is called _____________________________.
The force needed to overcome _______________ friction is usually less than that needed to overcome
________________friction.
VI. Gravity
A. Newton realized that a force acts to pull objects straight down toward the center of Earth.
________________ is the force that pulls objects toward each other.
B.
B. When the only force acting on a falling object is gravity, the object is said to be in ________________. An
object in free fall ________________ as it falls. In free fall the force of gravity is an __________________,
and unbalanced forces cause an object to _______________.
C.
C. How much do objects accelerate as they fall? Near the surface of Earth, the acceleration due to the
force of gravity is __________________.
D. While it may seem hard to believe at first, all objects in free fall accelerate at the
_________________________ regardless of mass.
VII. Air Resistance
A. Despite the fact that all objects are supposed to fall at the ______________________, you know that this is not
always the case.
1. An oak leaf flutters __________________ to the ground, while an acorn ______________ straight down.
2. Objects falling through air experience a type of fluid friction called ____________________________.
3. Air resistance is an _________________.
4. The __________________ the surface area of an object, the ________________ the air resistance. That
is why a leaf falls more slowly than an acorn.
B. Air resistance increases with __________________. Eventually, the air resistance ______________ the force
of gravity. Remember that when forces are balanced, there is no ___________________.
VIII. Growth of Seedlings
A. Have you ever noticed that most plants grow vertically—not sideways or downward? The reason is that plants
respond to the __________________. This response is known as ______________.
B. No matter how a young plant is positioned in the soil, its stem grows _____________ and its root grows
________________.
C. Roots grow in the direction of the _________________, whereas stems grow in the ________________
direction.
IX. Weight
A. The force of gravity on a person or object at the surface of a planet is known as ______________.
B. ______________ is a measure of the force of gravity on an object, and _____________is a measure of the
amount of matter in that object. Since weight is a force, you can rewrite Newton’s second law of motion,
Force = Mass × Acceleration, to find weight. Weight = Mass x Acceleration due to gravity ( W =mg)
C. Weight is usually measured in ______________, mass in ______________, and acceleration due to gravity in
____________. So a 50-kilogram person weighs 50 kg × 9.8 m/s2 = 490 Newtons on Earth’s surface.