# PHYSICS CH 4

an object will only accelerate if there is a net or unbalanced force acting upon it. the presence of an unbalanced force will accelerate an object – changing its speed, directions or both its speed and direction
what can cause acceleration in an object?
the resistance of any physical object to any chagne in its state of motion, including changes to its speed and direction. it is the tendency of objects to keep moving in a straight line at constant velocity. newton’s first law of motion
what is inertia
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a moving objejct will change direction if an unbalanced force acts upon it
what causes a moving object to change direction?
contact force
what force arises from direct physical contact between two objects?
1kg *m/s^2
what is the unit equivalent for a newton?
magnitude of the force
what does the length of a force vector represent?
show the relavtive magnitude & direction of all forces acting on an object in a given situation
what does a free-body diagram represent?
box
object’s representation in a free-body diagram
arrows
length of arrow proportional to magnitude of force
direction of arrow gives direction of force
each force arrow is labled & all forces acting on the object must be represented
force representation in a free-body diagram
forces that act on object, not the forces the object exerts itself on other objects
free-body diagram forces
add vectors in same direction; subtratc vectors in opposite direction
be able to determine the net force on a free body diagram
all objects upon earth experience a force of gravity that is directed “downward” towards the center of the earth
determine gravitational force on a free-body diagram
inertia
what is the term for an object to maintain its state of motino if not outside force acts upon it?
zero
a car goes forward along a level road at constant velocity. the additional force needed to bring the car into equilibrant force is what?
its a vector that is the exact same size as the resultant would be, but the equilibrant points in exactly the opposite direction
be able to calculate the equilibrant force
the upward acceleration of Earth is negligable because of its large mass
as an object falls toward Earth, what happens?
the object is accelerated
if a nonzero net force is acting on an object, then the object is what?
several forces combined
more than one force acting on an object
define net force
aimed to right
positive forces
aimed to left (canceled by positive forces)
negative forces
work together
forces in same direction
cancel each other
forces in opposite direction
work together
dont cancel each other
net force forces
inversely proportional
is acceleration directly proportional to or inversely proportional to the mass of the object
directly proportional
is acceleration directly proportional or inversely proportional to the net force of the object
force=ma
m=f/a
a=f/m
be able to calculate force, mass, and acceleration using F=ma
an object at rest will remain at rest unless acted on by an unbalanced force

an object in motion continues in motion with the same speed & in the same direction unless acted upon by an unbalanced force

“the law of inertia”

newton’s first law of motion
acceleration is produce when a force acts on a mass. the greater the mass (of the object being accelerated) the greater the amaount of force needed (to accelerate the object)

f=ma

Newton’s second law of motion
for every action there is an equal & opposite re-action.

for every force there is a reaction force that is equal in size, but opposite in direction.

whenever an object pushes another object, it gets pushed back in the opposite direction equally hard

Newton’s third law of motion
act on different objects
stimultaneous equal but opposite forces resulting from the interaction of two objects
what are action-reaction pairs?
the region of space surrounding a body

a charged particle or magnet, within which it cn exert a force on another similar body not in contact with it

what are field forces
hammer driving nail into piece of wood – hammer exerts force on nail; nail exerts force on hammer

leaf falls from tree and lands on sidewalk – leaf exerts force on sidewalk; sidewalk exerts force on leaf

ball dropped from person’s hand – earth exerts force on ball; ball exerts force on earth

give examples of action-reaction pairs
field forces
gravitational force and magnetism
mass
what is the measure of quantity of matter
weight
what is the magnitude of the gravitational force acting on an object
weight
a change in the gravitational force acting on an object
objects exert forces on each other when their fields interact
how does the theory of field forces explain how objects could exert forces on each other without touching
no units
what are the units of the coeffient of friction
force
newton of the SI unit of what physical matter
by arrows
how are force vectors represented in force diagrams
force causes an acceleration, or change in an object’s velocity.
applying the brakes decelerates the bicycle (accelerates it in negative direction) and causes a change in the bicycle’s velocity because the bicycle slows down
briefly describe how applying the brakes to stop a bicycle are an example of a force
the normal force and gravitational force vectors will cancel out in length, but the towing force vectors will be longer than the frictional force vector
construct a free-body diagram of a car being towed
scalar quantities contain only magnitude
forces have magnitude and direction
why is force not a scalar quantity
magnitude of the force
the length of the force vector is proportional to what property of a force
the object experiences an acceleration
what happens to an object in motion when it experiences a nonzero net external force
the same direction of the net force
in the equation f=ma, what is the direction of the acceleration
no, because the action force and the reaction force dont act on the same object.
the forces cancel only when they act on the same object
do action-reaction pairs result in a equilibrium?
mass will change, but weight can change depending on location
(you will weigh less on the moon as opposed to here on Earth due to the acceleration of gavity)
distinguish between mass and weight
if gravity is acting toward the center of the Earth (down) air resistance is acting upward (unless in a running scenario)
in what direction does the forece of air resistance act?
net force
what term is used to describe the vector sum of all the forces acting on an object?
for a falling object, air resistance is the friction that “stalls” free-fall movement

for a free-body diagram, a downward arrow would be drawn to represent the force due to gravity & an upward arrow drawn to represent the force of air resistance

why is air resistance considered a form of friction?
aimed in slanted direction
size of net force would not be the arithmatic sum of the sizes of the two other forces – use pythagorean theorem or trig to calculate net force
if several forces act on an object, they dont act on one line

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