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Psychics Exam Review
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Gravity
Chapters 2, 3, 4, 6
Terms in this set (53)
force
a push or pull (mass x 10) --> is needed to change an object's state of motion:
- unit of force is the newton (N)
force weight
when an object is pulled down onto a surface by gravity
net force
the combination of all forces acting on an object:
- a rock in your hand's net force is zero because the support force pushing up and the force of Earth's gravity pushing down cancel out
tension
a "stretching force"
tension force
when a string or spring pulls an object upwards
adding force
you may add or subtract forces if they act on each other along straight line
weight
the force of gravity acting downward on an object
vector
an arrow that represents the magnitude and direction of a quantity
vector quantity
a quantity that needs both magnitude and direction --> force
scalar quantity
a quantity that can be described by magnitude only and has no direction --> time, area, and volume
mechanical equilibrium
a state wherein no physical changes occur --> a state of steadiness
equilibrium rule
whenever the net force on an objects is zero (ΣF=0), the object is said to be in mechanical equilibrium:
- the Σ stands for "the sum of"
- the F stands for "forces"
support force
the upward force that balances the weight of an object on a surface --> often called "normal force"
static equilibrium
objects at rest --> the net force is 0 newtons
dynamic equilibrium
objects moving at a constant speed in a straight line
Aristotle
created the idea of natural and violent motion, did not recognize inertia
Newton
developed the law of inertia
Galileo
was on of the first to recognize that no force was needed to keep an object in motion
violent motion
was imposed motion --> the result of forces that pushed or pulled
natural motion
straight up or straight down -->a boulder facing toward the ground, or a puff of smoke rising
motion of a falling object
Galileo hypothesized that two objects will fall at the same rate if air resistance is zero
friction
force that acts between materials that touch as they move past each other
inertia
the property of a body to resist changes to its state of motion --> relates mostly to mass
newton's first law
(the law of inertia) states that a force is not needed to keep an object moving
amount of inertia
the more mass an object has --> the greater its inertia is
kilograms
the unit of mass
mass
the quantity of mass matter in an object --> the measure of inertia of an object:
- larger mass will be more difficult to move than a lesser mass
relative motion
the idea that objects seem to move differently depending on your motion --> like a rower moving diagonally
speed
how fast an object is moving --> expressed as distance/time
instantaneous speed
the speed of an object at any instant --> the speedometer on a car
average speed
the total distance covered divided by the time --> 80 km/2h = 40 km/h
total distance covered
average speed x travel time
velocity
a speed in a given direction: is either an object's speed OR its direction (or both) is changing, then the object's velocity is changing --> a vector quantity
speed vs. velocity
speed is a description of how fast an object moves; velocity is how fast and in what direction it moves
constant speed
steady speed
constant velocity
both constant speed AND constant direction in a straight line
acceleration
the rate at which the acceleration is changing = change of velocity/time interval:
- directly related to net force
- related to decrease and increases
- change the state of motion of an object by changing its speed, its direction or motion, or both
- expressed in km/s/s
IF WE CHANGE SPEED, DIRECTION, OR BOTH, WE CHANGE VELOCITY AND ACCELERATE
free fall
when a object moves under the influence of gravitational force:
- the acceleration of an object in free fall is 10 m/s/s
- when a n object is thrown up, the acceleration is 10m/s/s
- the instantaneous speed of an object that is at its highest point when thrown up is zero
- at the end of time, an object in free fall has fallen an distance equal to 1/2gt^2
elapsed time
the time that has elapsed, or passed since the beginning of any motion
air resistance
the force that presses against a falling object --> the friction acting on something moving through air: applies to liquids
- depends on the object's speed and area
- "all freely falling objects fall with the same acceleration because the net force on an object is only its weight, and the ratio of weight o mass is the same for all objects"
v = at
velocity of a free falling object
d = 1/2at^2
distance for a free falling object
difference between speed and velocity
______ is how fast the object is moving and ______ is how fast the object is moving AND in which direction
difference between velocity and acceleration
_____ is how fast the object is moving and in which direction and _____ is rate at which it's changing
inversely
means that two values change in opposite directions --> 1/mass
directly
means that two values change in the same direction --> mass/1
newton's second law
describes the relationship among an object's mass, and object's acceleration, and the net force on an object. states:
- the acceleration produced by a net force on an object is directly proportional to the magnitude of the net force, is in the same direction as the net force, and is inversely proportional to the mass of the object --> acceleration ~ net force/mass
fluids
liquid or glasses that "flow"
free body diagram
a diagram showing all the forces acting on an object
pressure
the amount of force per unit of area --> pressure = force/area of application:
- a book exerts the same force, but greater pressure agains the suppuration surface when laid flat or on it's side
pascals
(Pa) the unit used to describe pressure
terminal speed
the speed at which the acceleration of a falling object is zero because friction balances the weight
terminal velocity
is terminal speed together with the direction of motion
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