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Physics 1 Exam 1 Review (Mod 1-3) (Ch 1-4)
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Gravity
Terms in this set (95)
what is motion and what are the four types
change of an object's position over time
1. straight-line
2. circular
3. projectile (air)
4. rotational (axis)
for projectile motion in y direction only, what do we know about initial velocity
initial velocity of an object thrown upward will be positive, thrown downward will be negative, and "dropped" will equal 0
for projectile motion, what do we know about ax and ay
ay is -g
ax is 0
what is the range equation and when does it apply
∆x = (Vo^2sin2(theta))/g
what is only kinematic equation not given to us
∆x=Vft-(1/2)at^2
how can you tell from a motion diagram whether an object is speeding up, slowing down, or going at a constant speed?
motion diagram shows object's positions at several equally spaced instants of time
so if distance between each image is same: constant speed
if distance between images is increasing: speeding up
if distance between images is decreasing: slowing down
what is position
what is origin
how do you tell your position
position = location at a particular instant in time (reported as + or - so you know which direction you're moving in)
origin = fixed reference point, from where distance is measured
to give position, tell origin, distance from origin, and direction
what is displacement
change in position (∆x = Xf - Xi)
can ∆t be negative
no bc time always passes as an object moves from Xi to Xf
what is uniform motion
how do you calculate speed in this situation
how do you calculate average velocity of a moving object for this situation
what does position graph look like
equations for uniform motion do not have what variable
is this uniform motion: go 2mph for 2 seconds and then stop for 6 seconds and then go 2mph for another 2 seconds
constant speed (velocity), straight-line motion, for whole time interval
(distance traveled in a given time interval)/(time interval)
(displacement)/(time interval) = ∆x/∆t
straight line
acceleration and don't have ∆V bc V doesn't change, only Vx (or Vy)
no bc even tho 2mph twice, you stop so not constant velocity the whole time
what is the difference between speed and velocity
velocity has a direction (+ or -) while speed does not (it is always positive)
significant figures
when multiplying or dividing, the number of sig figs in the answer = ?
when adding or subtracting, the number of decimal places in the answer = ?
# of sig figs of least precisely known value used in calculation
smallest # of decimal places of any value used in the calculation
interpreting a position graph
what is the slope of a position graph
what does a negative slope mean
what does a horizontal line mean
what does a positive slope mean
what does a steep slope mean compared to a less steep slope
velocity
car is traveling left (velocity is negative)
at rest (slope is 0 so velocity is 0)
moving right (velocity is positive)
steeper slope means faster speed
what is the difference between a scalar and a vector
a scalar is just a value, it has a magnitude but not a direction
a vector has both a magnitude and a direction
the magnitude of a velocity vector is also known as...
speed (bc no direction)
if an object is moving to the right then (Vx/Vy) is (</>/=) 0
if an object is moving to the left then (Vx/Vy) is (</>/=) 0
if an object is moving up then (Vx/Vy) is (</>/=) 0
if an object is moving down then (Vx/Vy) is (</>/=) 0
Vx>0
Vx<0
Vy>0
Vy<0
velocity graph
what does a horizontal line mean
what do multiple horizontal lines at different y-values mean
constant velocity (showing slope of position graph)
instant changes in velocity (not realistic)
what does area under the curve mean in terms of position, velocity, and acceleration curves?
area under velocity curve for a given time interval is displacement (∆x)
area under acceleration curve for a given time interval is change in velocity (∆V)
what is instantaneous velocity on a position graph
slope of line tangent to curve at that instant of time
what is acceleration
what does constant acceleration look like on velocity graph
what does steepness of slope of velocity graph tell us about acceleration
what does horizontal line of acceleration graph means
rate of change of velocity, slope of velocity graph, ∆V/∆t
straight line
steeper V graph means higher acceleration
velocity is changing at a constant rate, velocity graph is a straight line (if horizontal acceleration graph is at y-value of 0 then velocity is constant but if + or - then velocity is changing)
the velocity vector and acceleration vector point in the same direction for objects that are (speeding up/slowing down)
speeding up
the velocity vector and acceleration vector point in opposite directions for objects that are (speeding up/slowing down)
slowing down
what is free fall
all objects in free fall have the same ___, regardless of ___
explain symmetry when object goes up and then comes down
when is velocity zero
what is formula for ymax
when an object moves under the influence of gravity only, no other forces (ex: air resistance)
acceleration; mass
velocity is same for both halves (w opp signs) and time is same for both halves
at max height
ymax = (Vi)^2/(2g)
tell whether the following is an example of free fall:
ball falling thru air
ball tossed straight up
ball in projectile motion (basketball free throw)
satellite in orbit
feather falling in sky
skydiver falling w open parachute
hammer thrown up on moon
yes
yes
yes
yes
no (air resistance)
no (air resistance)
yes (there is still gravity on moon)
if drop two balls from top of building and one weighs 1kg and the other weighs 0.5 kg, which will hit ground first
will hit at same time bc all objects in free fall have same acceleration regardless of mass
an object dropped from rest is (speeding up/slowing down) so its acceleration and downward velocity point in (same/opposite) direction so ax points (up/down)
speeding up
same
down
an object initially moving up is (speeding up/slowing down) so its acceleration and downward velocity point in (same/opposite) direction so ax points (up/down)
slowing down
opposite
down
acceleration in free fall points which direction
down, always, regardless of what direction object is moving
what is a vector
can the magnitude of a vector be negative
how can two vectors be equal
multiplying a vector by a positive scalar does what
multiplying a vector by a negative scalar does what
straight line from initial position to final position (actual path taken may have been curved)
no
if same magnitude and direction, regardless of starting point
gives a vector of different magnitude but pointing in same direction
change direction but keep same magnitude
when moving down a ramp, velocity vectors point in what direction
is object speeding up or slowing down
which direction does ax point
how do you find acceleration for ramp motion
in direction of motion, downhill, parallel to ramp
speeding up
same direction as Vx
acceleration is not just g bc there is now an x and y component so ax = (+/-)gsin(theta) where +/- depends on direction ramp is tilted meaning if moving right or left and ay=g
what is commutative law and how does it apply to vectors
what about associative law
a + b = b + a
(a+b)+c = a+(b+c)
means can add vectors in any order and get same answer, even graphically
if given magnitude of velocity or acceleration vector, how can you find the x and y components
how can you find theta
Vx = Vcos(theta)
Vy = Vsin(theta)
tan(theta) = Vy/Vx
PAY ATTENTION TO SIGNS (+/-)
if you cover no distance (round-trip), what does that mean about average velocity
Vavg = 0 m/s but still have speed
this is bc whatever velocity you had on way there, you had same thing on way back but negative so they cancel out
average acceleration is 0 when...
starting and ending Vx is 0
projectile motion
horizontal velocity has no effect on...
acceleration's x and y components are...
made up of two different independent motions:
how does mass play a role
how is time different for horizontal and vertical motion
vertical motion (and vice versa)
constant. ax=0 and ay=-g=-9.8
uniform motion at constant velocity in horizontal direction and free fall motion in vertical direction
it doesn't!
time is same for horizontal and vertical motion
if launching a projectile, launching at an angle above the horizontal does what
gives more time in air so can give greater distance
what is range
what two variables determine it
at very small or very large angles, range is _______
max range achieved at ___° but only if ...
launch angles of ___ and ____ give same range
for small objects at high speeds, _____ makes optimal angle less/more than number above
time that projectile is in air is determined by ____.
horizontal distance covered by a projectile
initial speed and launch angle
quite small
45° but only if landing is at same elevation as launch
theta and 90°-theta
air resistance; less
y-component of launch velocity, it takes longer to go higher
if one object is thrown to the right and other is dropped straight down, which will hit ground first and why
will hit at same time bc both are in free fall so both have ay=-9.8
true or false: vertical and horizontal components of projectile motion depend on each other
false
they are independent
dynamics is the study of ___ which combines with _____ to form ____ which is the general science of motion
forces
kinematics
mechanics
if you apply force to object causing it to move, what will be the difference if there is or isn't friction
if there is friction then object will eventually come to a stop
if there is no friction then object will stay in motion
what is Newton's first law
assuming an object has no forces acting on it, if it is at rest it will stay at rest and if it is moving, it will continue to move in a straight line at constant speed
F(net)=0 = V is constant
true or false: you need applied force to keep an object in motion
false
if apply force once and then no other forces acting on it like friction, air resistance, etc., object will keep on moving forever
friction or air resistance usually cause an object to stop moving, not lack of applied force
what is a force
forces act on _____
it requires an ___
is force a scalar or vector
what is the difference between a contact force and a long-range force
a force is a ___ betwn two objects. what does this mean
a push or pull
objects, forces don't exist w out objects they r acting on
agent (cause, thing that does the push or pull) (can be inert, inanimate objects)
vector
contact force: force acts on object by touching it
long-range force: force acts on object w out physical contact (magnetism, gravity)
interaction; if agent exerts force on an object, object exerts force on the agent
true or false: pushing and pulling forces are drawn the same in free body diagrams
yes, same direction
what is weight
what type of force is it
what is the agent of this force
which way does weight vector point
the gravitational pull of the earth on an object on or near the surface of earth
long-range
the entire earth
always points straight down (even if on incline, not along y-axis)
what is spring force
what type of force is it
how does it push and pull
can be metal coil but also like bendy ruler that "springs" back into place
contact force
pushes when compressed and pulls when stretched
what is tension force
what type of force is it
what direction does force point
when a string, rope, or wire pulls (not push) on an object
contact force
direction is always direction of string/rope
what is normal force
what direction is it in
what is agent
force exerted on object that is pressing against a surface
always perpendicular to surface (even on incline)
surface
what are the two types of friction force
what direction does friction force point
it is always parallel to _____
kinetic friction: acts as an object slides across a surface
static friction: keeps object "stuck" on a surface and prevents motion relative to surface
kinetic friction points in opp direction of object's motion
static friction points in opp direction that object WOULD move if no friction; aka points in direction needed to prevent motion
the surface
what is drag force
what direction does it point in
when is value of drag force large or small
resistive force (opposes motion) of a fluid (gas or liquid) on a moving object
points opp to direction of motion
large for objects moving at high speeds or in dense fluids (feather)
small for objects that are heavy and compact moving in air (ball)
what is thrust force
what type of force is it
what is agent
in which direction does it point
when a jet or rocket engine expels gas molecules at high speeds
contact force
exhaust gas that pushes on engine
points opposite the direction in which the exhaust gas is expelled (so points in direction of motion)
what are electric and magnetic forces
long-range forces that act on charged particles
an object pulled with ___________-, moves with constant acceleration
constant force
how are acceleration and force related
if force is doubled, what hap to acceleration
how are directions of each related
directly proportional
doubles
point in same direction
how are mass and acceleration related
if double mass, what hap to acceleration
indirectly proportional
halved
as mass gets larger, what hap to acceleration
approaches 0
as mass gets smaller, what hap to acceleration
gets very large
what is inertia
do more massive or less massive objects have more inertia and why
tendency to resist a change in velocity (speeding up or slowing down or going from rest to being in motion)
more massive bc it's harder to change their velocity (takes more force)
what is Newton's Second Law
F=ma
if a net external force acts on an object, the object accelerates in the direction of the applied force
what is unit of force
Newtons which equal (kg x m)/(s^2)
what is Newton's third law
every force occurs as one member of an action/reaction pair of forces
meaning for every action there is an equal and opposite reaction
for newton's third law,
what do forces act on
what direction do they act in
how are their magnitudes related
how do acceleration and mass play a role here
can this apply to long-range forces
which force type are we talking about for each object
2 separate forces acting on different objects
point in opposite directions
have equal magnitude
they don't, we are just talking about equating two forces (not mass or acceleration). so even if one object is very massive and other is very small, they still put same force on each other (just have different accelerations based on difference in mass)
yes
action force must be of the same type on both objects
what are the steps to solving problems w newton's second law (F=ma)
1. draw force diagram and sep x and y components where needed
2. write Fnetx and Fnety
3. set net force equal to ma or 0 (if object not accelerating in direction of net force)
4. solve
when solving for x and y components of weight on an incline, what is important to note
angle is based off y axis not x so sin and cos are switched so Wx=wsin(theta) and Wy=wcos(theta)
friction is equal to what
(mu)n
where n is normal force and mu is a constant
how are weight and mass different
weight is a force (a vector) while mass is a scalar
weight changes based on gravity so different on different planets but mass is always same
mass describes inertia (tendency to resist being accelerated) while weight is gravitational force exerted on an object by a planet
weight = w= ?
mg
pounds are a unit of ___
kilograms are a unit of ___
force
mass
so can't convert between the two easily
what is apparent weight
what causes it
w(app) = ?
what role does acceleration play here
explain how a scale tells you your weight
how heavy you "feel"
caused by contact forces supporting you (not gravity bc you can't feel that)
w(app) = w + ma(y)
if ay is negative, w(app) is less than w so you feel lighter than normal. if ay is positive, w(app) is greater than w so you feel heavier than normal)
it tells you the upward force of the scale on you (supporting contact force meaning apparent weight) and bc you aren't accelerating, that is equal to w (your actual weight)
when you accelerate upward, you feel ____
heavier
in a pulley problem, where M1 is lighter box and M2 is heavier, what is acceleration of M1 equal to
((m2-m1)/(m2+m1))(g)
in a pulley problem, where M1 is lighter box and M2 is heavier, what is Tension force equal to
((2m1m2)/(m1+m2))(g)
if normal force is only contact force supporting you then what is it equal to
weight + m(ay)
on a scale, apparent weight = what
normal force
when you accelerate downward, you feel ____
lighter
what is apparent weight in free fall
zero bc no supporting contact surfaces
what is weightlessness
no apparent weight
but still have mass
if w(app) is greater than w, acceleration is positive/negative
positive
if w(app) is less than w, acceleration is positive/negative
negative
what is net force
VECTOR sum of all forces acting ON an object
so need to take x and y components of force vectors into account
and don't count forces the object in question applies to other objects
if you double net force, what hap to acceleration
doubles
does weight exist w out gravity
no but mass does
what does position graph look like when starting w positive velocity and speeding up
curve up
what does position graph look like when starting w positive velocity and slowing down
increasing up but then leveling off
what does position graph look like when starting w positive velocity and constant speed
straight line w pos slope
what does position graph look like when starting w negative velocity and speeding up
curving down
what does position graph look like when starting w negative velocity and slowing down
curving down but leveling off
what does position graph look like when starting w negative velocity and constant speed
straight line w neg slope
what does velocity graph look like when starting w negative velocity and speeding up
straight line w neg slope
what does velocity graph look like when starting w negative velocity and slowing down
straight line w pos slope
what does velocity graph look like when starting w negative velocity and constant speed
horizontal line in quadrant 4
what does velocity graph look like when starting w positive velocity and speeding up
straight line w pos slope
what does velocity graph look like when starting w positive velocity and slowing down
straight line w neg slope
what does velocity graph look like when starting w positive velocity and constant slope
horizontal line in quadrant 1
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