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Gravity
Chapters 2-8 in Conceptual Physics
Terms in this set (74)
A force is needed to
change an objects state of motion
The combination of all forces acting on an object is called the
net force
When you hold a rock at rest in your hand, you are pushing upward on it with as much force as Earth's gravity pulls down on it. The net force would be
zero on the rock
The scientific unit of force is the newton--
abbreviated N
Tension is a
stretching force
Weight is the force of gravity
acting downward on an object
A vector is an arrow that
represents the magnitude and direction of a quantity.
A vector quantity is a quantity that needs both magnitude and
direction for a complete description
-an example would be force
A scalar quantity is a
quantity that can be described by magnitude only and has no direction. -time, area, and volume are scalar quantities
You can express the equilibrium rule mathematically as
(funky backwards E letter)F=0
-e letter stands for the sum of
-f stands for forces
Mechanical Equilibrium is a
state wherein no physical changes occur; it is a state of steadiness
Whenever the net force on an object is zero, the object is said to be in
mechanical equilibrium
What is the Equilibrium Rule?
Whenever the net force on an object is zero, the object is said to be in mechanical equilibrium
For a suspended object at rest, the forces acting upward on the object must be
balanced by other forces acting downward to make the vector sum equal zero
For an object at rest on a horizontal surface,
the support force must equal the objects weight
A support force is the upward force
that balances the weight of an object on a surface. A support force is often called the normal force
An upward support force is
positive and a downward weight is negative
-The weight of a book sitting on a table is a negative force
-The atoms squeeze
-The compressed atoms produce
-that squeezes downward on the atoms of the table
-upward on the book.
-the positive support force.
Objects at rest are said to be in
static equilibrium
Objects moving at constant speed in a straight line path are said to be in
dynamic equilibrium
Equilibrium is a state of
no change
An object under the influence of only one force
cannot be in equilibrium
Only when there is no force at all, or when two or more forces combine to zero, can
an object be in equilibrium
Both static equilibrium and dynamic equilibrium are examples of
mechanical equilibrium
The Parallelogram Rule
to find the resultant of two nonparallel vectors, construct a parallelogram wherein the two vectors are adjacent sides. The diagonal of the parallelogram shows the resultant
Resultant
the sum of two or more vectors
Combining vectors is simple when they are parallel.
-If they are in the same direction
-If they are in opposite directions
-they add
-they subtract
To find the resultant of nonparallel vectors
use the parallelogram rule
When applying the parallelogram rule to two perpendicular vectors that are equal in magnitude
-the parallelogram is a square.
The resultant is root 2, or 1.414, times one of the vectors
When an object is suspended at rest from two non-vertical ropes, there are three forces acting on it:
1. a tension in the left rope,
2. a tension in the right rope
3. the object's weight.
The resultant of rope tensions must have the same magnitude as the objects weight.
Aristotle
the foremost Greek scientist
-studied motion and divided it into two types
--natural motion
--violent motion
During Aristotle's time, natural motion on Earth was thought to be
either straight or straight down: It was 'natural' for heavy things fall and fog very light things to rise
Violent Motion
was imposed motion and it was the result of forces that pushed or pulled
The proper state of objects was thought to be one in rest, unless they were being
pushed or pulled or were moving towards their natural resting place
Copernicus reasoned that the simplest way to interpret astronomical observations was to assume
that Earth and the other planets move around the sun
Copernicus' idea of motion in space was extremely controversial at the time, because most people believed that
Earth and the other planets move around the sun.
Copernicus worked on his ideas in secret to escape
persecution. At the urging of his close friends, he published his ideas
Galileo argued that only when friction is present
as it usually is, is a force needed to keep an object moving
One of Galileo's greatest contributions to physics was
demolishing the notion that a force is necessary to keep an object moving. A force is any push or pull.
Friction
the force that acts between materials that touch as they move past each other
-Galileo found that a ball rolling on a smooth horizontal plane has almost constant velocity, and if friction were entirely absent
-Galileo also stated that the tendency of a moving body to keep moving is
-the ball would move forever
-natural and that every object resists change to its state of motion
Inertia
the property of a body to resist changes to its state of motion
Newton's First Law
every object continues in a state of rest, or of uniform speed in a straight line, unless acted on by a nonzero net force
Isaac Newton's laws of motion
replaced the Aristotelian ideas that had dominated thinking for about 2000 years
Another name for Newton's First Law
Law of Inertia
Forces are needed to
overcome any friction that may be present. Forces are also needed to set objects in motion initially
Once an object is moving in a force-free environment, it will
move in a straight line indefinitely
The more mass an object has, the greater
its inertia and the more force it take to change its state of motion
Mass
-the quantity of matter in an object
-measure of the inertia of an object
-measure in the fundamental unit of kilograms
Weight
-the force of gravity on an object
-depends on an object's location
-same whether the object is located on earth, the moon, or in outer space
Mass and Weight are proportional to each other in a given place.
Objects with great mass have great weight; objects with little mass have little weight
In most parts of the world, the measure of matter is commonly expressed in units of
mass. The SI unit of mass is the kilogram and its symbol is kg.
The SI unit of force is the
newton
The SI unit for the newton is
N and is written with a capital letter because it is named after a person
The Law of Inertia states that
objects in motion remain if no unbalanced forces act on them
Copernicus announced the idea of a moving Earth in the 16th century..
this controversial idea stimulated much argument and debate
Newton's work showed that objects on Earth move
with Earth as Earth moves around the sun. The Law of Inertia also shows that objects within moving vehicles move with the vehicles
Notions of motion today are very different from
those of our distant ancestors.
An object is moving if
its position relative to a fixed point in changing
When we describe the motion of one object with respect to another,
we say that the object is moving relative to the other object
Unless stated otherwise, when we discuss the speeds of things in our environment
we mean speed with respect to the surface of Earth
You can calculate the speed of an object by
dividing the distance covered by time
Galileo is credited as being the first to measure speed
by considering the distance covered and the time it takes
Speed
how fast an object is moving
Any combination of units for distance and time that are useful and convenient are
legitimate for describing speed
Some units that describe speed are: The slash is read as :
-mph and kph
-per
Average Speed
total distance covered divided by the time
-does not indicate variations in the speed that may take place during the trip
total distance= average speed*travel time
Speed is a description of how fast an object moves;
velocity is how fast and in what direction it moves
Velocity
speed in a given direction
A quantity such as velocity, which specifies direction as well as magnitude, is called
vector quantity
Scalar Quantity
quantities that require only magnitude for a description
Constant Speed
means steady speed
Constant Velocity
means both constant speed and constant direction, which is in a straight line
If either an objects speed or its direction is changing
then the objects velocity is changing
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