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Physics/Trujillo Semester Review
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Gravity
Key Concepts:
Terms in this set (74)
motion is relative
even things that appear to be at rest move
speed
is a measure of how fast things are moving (speed equals distance over time) (mi/h, km/h, sec)
instantaneous speed
the speed at any instant
average speed
the average speed over time (a.s = total distance covered over time interval)
velocity
speed with direction - 30 mph north, change velocity by changing either speed or direction (m/s)
time
the rate at which velocity is changing is acceleration (applies to changes in direction in speed)
constant velocity
motion remains at the same speed
changing velocity
speed or direction (or both) is changing
acceleration
can be a decrease or increase in speed or change in direction (acceleration equals change of velocity over time interval) (m/s^2, km/h x s)
free fall
is motion under the influence of the gravitational force only
gravity's acceleration rate
9.8~10
how fast v=at
how far d= 1/2at^2 (a=gravity)
weight
is the force of gravity on an object (mass x acceleration)
mass
a measure of an objects inertia; also a measure of the amount of matter in an object (kg) MASS IS NOT WEIGHT NOR VOLUME
projectile motion
any object that moves through the air or or through space, acted only by gravity (and air resistance if any)
vector quantity
quantity with magnitude and direction, velocity
scalar quantity
quantity with magnitude (amount) only, speed
wind = 60 km/h west
plane = 40 km/h west
what is the total velocity?
total velocity = 100 km/h west
wind = 60 km/h west
plane = 40 km/h east
what is the total?
total = 20km/h west
parallelogram method
1. draw the two vectors so their tails touch
2. use a dash line to make a parallelogram
3. draw the resultant vector
4. use Pythagorean theorem
a^2 + b^2 = c^2
the horizontal and vertical component of motion are
independent
newtons first law-inertia
An object at rest stays at rest and an object in motion stays in motion unless acted upon by an outside motion.
inertia
is related to the first law because its an objects resistance to change motion
force
any push or pull; gravity, magnetic force, kinetic force, electrical, nuclear (newton)
1 kg =
9.8 newtons
newtons second law-force and acceleration
the acceleration produced by a net force on an object is directly proportional to the magnitude of the net force
acceleration = change in velocity over time interval
net force causes
acceleration, and mass resists
acceleration = net force of mass
a = f/m
f = m x a
force
newtons, N
mass
kilograms, Kg
acceleration
m/s^2
friction
is a force that affects motion, air resistance is friction acting on something that moves through air
pressure
the amount of force per unit area
pressure = force/area of application
what happens when you double force
you double acceleration
what happens if you double mass
acceleration is halved
why does it hurt when you walk on heals
the is not an equal amount of force being spread on heels than on flats
what do you do when walking on ice and it starts to crack?
lay down, it applies even pressure
newtons third law-action and reaction
every action has an equal and opposite reaction
action: object a exerts a force on object b
reaction: object be exerts a force on object a
a: i push cart
a: i pull the rope
a: i slap your face
r: cart pushes me
r: rope pulls me
r: your face slaps me
One object has twice as much mass as another object. The first object also has twice as much
inertia
accelerations are produced by
forces
acceleration is inversely proportional to
its relation to its mass
work
the product of force on an object and the distance through which the object is moved
work = quantity force x distance
unit = joules
power
rate at which work is done, or energy is transferred
power = work done / time interval
unit = watts
mechanical energy
the energy due to the position or the movement of something; potential or kinetic energy
potential energy
energy of position, usually related to the relative position of two things, such as stone and earth, or an electron and a nucleus
PE= weight x height
kinetic energy
energy of motion, equal to half the mass multiplied by the speed squared
KE= 1/2mv^2 (mass x speed)
law of conservation of energy
energy cannot be created or destroyed only transferred
PE is indirectly proportional to KE
PE decreases as KE increases
machine
simple device that makes work easier.
fishing line, scissors, knife, lever, pulley
mechanical advantage
input distance over output distance
if you lift two loads up one story, how much work do you do compared to lifting just one load up one story?
twice as much
if you push an object with twice the force for twice the distance you do..
four times the work
How much farther will a car traveling at 100 km/s skid than the same car traveling at 50 km/s?
four times as far
1 liter of h2o has a mass of 1 kg and a weight of 9.8 N
therefore it will displace 1 liter and have a buoyant force of 9.8 N
pressure
pressure = force over area
the pressure of a liquid depends on
the density and depth of a liquid
why does a one meter deep pool have more density than a 0.5 meter deep ocean?
because pressure depends on depth not volume
buoyancy
the apparent loss of weight of objects when submerged in a liquid
buoyant force
the upward force exerted by a fluid on a submerged or emerged object
the buoyant force on an object is least when the object is
submerged near the surface
how to find volume?
figure out how much water that object displaces
Archimedes principle
the relationship between buoyancy and displaced fluid
pressure in a liquid depends on
depth and density
what determines whether or not an object floats?
depth
pascals principle
you cannot pressurize a liquid.
changes in pressure at any point in an enclosed fluid at rest are transmitted undiminished to all points in the fluid and act in all directions
gases and liquids are both
fluids
air pressure would be the highest where?
closest to the surface
how do buoyancy for gases and liquids compare?
its the same concept
Bournoulli's principle
the pressure in a fluid decreases as the speed of the fluid increases
above a birds wing is
a low pressure zone, (fast)
below a birds wing is
high pressure zone, (slow)
air pressure is less above the wing than
below it
why can an airplane fly?
lift is greater than gravity; thrust is greater than air resistance
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