unit 1 kinematics Flashcards
Scalar vs. vector
scalar = absolute value and MAGNITUDE (speed, distance, calories etc)
vector = direction, positive and negative depending on the problem (displacement + or -, acceleration or deceleration (+ or - acceleration), velocity, etc.)
Is force a vector?
yes (5 N up or down)
Often vectors will be indicated on variables by:
having an arrow above the variable (ex. a v with an arrow pointing right over it)
mass vs. weight (and if scalar or vector)
Mass: scalar, absolute MATTER within an object
weight: vector, the force applied DOWNWARDS as a function of mass
define resultant vector
the net vector after you’ve, like, added and subtracted the vectors along the same axis, and stuff
When calculating resultant vector, saying, for example, north of east, is enough.
(true/false)
FALSE, you must have a DEGREE to describe the vector. ALSO don’t use NE, use north of east or east of north for specificity as to where the angle is from.
Tip to tail method vs.tail to tail (parallelogram method)
tip to tail: draw hypotenuse
tail to tail: fill in missing sides to make a parallelogram, create median line to end of parallelogram corner
how to subtract vectors (A-B)
B is negative, thus opposite direction. add A to B flipped in the opposite direction.
what does imaginary number, i, mean in a vector?
turn 90 degrees toa d ifferent dimension, if you use one imaginary it goes to a different dimension, if you turn 180 degrees you go backwards, which makes it negative
Do horizontal and vertical vectors impact each other?
No, regardless of the horizontal speed an object fired will remain accelerated the same by gravity
Determine an expression for the horizontal distance traveled D in terms of H, Vx, and g (projectile launched horizontally off of a table at height H at speed V)
D = V*(sqrt(2H/g))
because
delta x = V0*(t)
and delta y = 1/2gt^2
How to use components in an equation for a projectile launched at an angle
x = v0cos(theta)(t)
y = v0sin(theta)(t) + (1/2)gt^2
How to find uncertainty of multiplied/divided parameters? (square with uncertain sides)
add/subtract uncertainties to parameters (to create the biggest/smallest result), and go with the larger calculated uncertainty (higher vs. lower) (overestimate uncertainty)
Given a same initial velocity and height, objects fired at angles which add up to 90 degrees will move the same horizontal distance
(true/false)
true
list the kinematic equations
v = v0 + at (no x)
x = x0 + v0x + (1/2)at^2 (no v)
vf^2 = v0^2 + 2a(x-x0) AKA delta x (no t)
type 1 vs type 2 vs type 3 projectile motion
Type 1: horizontal only launch off of a given height (no angle)
Type 2: launched with an angle
Type 3: launched with an angle at a given height
FINDING WEIGHTED AVERAGE
definition of a force
interaction between two objects tending to cause acceleration if unopposed (push or a pull). these can exist without physical contact (gravity, electromagnetic, etc.) or with (tension, friction, applied force)
units of force
NEWtons (N) (metric), or (kg*m)/ s^2
lbs (imperial)
what’s the most common way to solve a physical sense problem such as:
Doesthe below equation make physical sense?
vf = ((1/2)x * t)/force
does it make physical sense? does lowering the force applied cause it to speed up or slow down? we know that increased time over the same distance = lower final velocity, so that doesnt makes sense, and neither does an increase in force causing lower velocity. also, the units dont make sense in velocity’s m/s if force isn’t somehow cancelled out, and with time in the numerator.
Newton’s first law and inertia
object at rest stays at rest, in motion stays in motion, inertia = the resistance to a CHANGE IN MOTION of an object
if the sum of the forces is zero, then acceleration…
is zero
if acceleration is zero, then the sum of the forces…
is zero
equilibrium in physics is:
a nonchanging velocity
how come you can pull the rug out from an object and not move it?
force is effectively an accelerant across a given time, and therefore pulling the rug out from a beaker fast enough will not transfer enough force to topple it over
Two spaceships pull cargo pods, one full and one empty. The speeds are constant, 300 m/s and 500 m/s. All masses are given in terms of M, the mass of an empty cargo pod. This is space so there are nor resistive forces. Rank the tension in the connecting cables at locations A, B, C, and D
1:
pod 2(M) —A—-pod 1(2M)——b—–engines
mSHipA = 7M
2:
pod 2(2M)—–C—–Pod 1(M)—–D—–engines
mShipB = 6M
None, trick question, its at a constant velocity, and with no resistive forces = engines not on = all things constant = no tension due to no fORCE
Does newton’s 1st law hold true in every reference frame?
no, such as in a room if the earth stopped spinning you’d see everything accelerating for no reason but in reality it was the earth changing its velocity and decelerating . where newtons 1st law works is where ACCELERATION is zero and velocity is constant. its all about what you use to compare things, or what tREFERENCE FRAME you use
when two ropes hold up a mass, and one is at a more horizontal angle, which one has greater tension?
the less horizontal one because the y component is larger compared to x, and if the x’s are equal x^2 + y^2 = c^2, if one leg is equal then the larger vertical is larger overall (and hypotenuse must always be larger than any one leg)
two sets of ropes hold up the same mass. of the set that is more vertical and the two that are more horizontal, which have more tension?
the more horizontal ones, as there is more force in the x direction on top of the downward force
when can you NOT treat object systems like single objects in regards to force of tension of rope A in stuff with like ropes A, B, C, and D?
when acceleration is different or in determining internal forces
in the equation F = ma, what is the slope? how is that determined?
m, as that is the most physically informative when graphed. Even though other variations of that equation are correct, such as m = a/F, this would make the equation’s x, y and m values less visible
newtons second law
acceleration is inversely proportional to mass, and proportional directly to NET force
a = (sum F )/m (makes sense w/cause and effect, larger force = more acceleration and more mass = more inertia = less acceleration)
or
sum F = ma
F=ma
tips/steps of Newtons second law
- Free body diagram
- vectors —> components
- equations of motion = + and - vectors fpr NET FORCE, larger- smaller
- solve for unknowns
what is friction caused by?
combination of two processes, imperfections in surfaces sliding across each other, and molecular forces (van der waals)
what are the types of friction? whats the difference?
static vs. kinetic,
static - keeps at rest, stops something from moving until overcome
kinetic - friction during motion after static is overcome
true/false
kinetic friction is larger than static friction
FALSE, STATIC is usually larger, few times it would be about the same, though probably never a situation where static is LESS
friction equation
Ffriction = mu(slope, coefficient of friction) x Fn
does mu/coefficient of friction have units?
nah, GENERALLY goes from 0 to 1 (more than 1 is like literally adhesive) (attribute of materials)
does surface area, speed, or temperature impact friction or coefficient of friction?
no (though they CAN, our system is simplified and for this class we assume nah)
do tires rolling on a road use kinetic or static friction?
static, point of contact never changes, not actively sliding without gripping (opposite of this would be like burnout or drifting)
Kinetic vs. static friction equations
Kinetic: fk = Mk(Fn)
mu x Fn = constant if in motion and surfaces are sliding, regardless of acceleration or other state of motion
Static: fs <=Ms (Fn)
mu x Fn = LIMIT of static force, if you go over it starts moving, you can pull with less than that and it still shouldn’t move and thus friction is kept in equilibrium
true/false: friction is always less than normal force
true, look at the equation dumbo
what do delta x and delta y equal when a projectile is launched HORIZONTALLY (equations)?
Using kinematic #2: (x = x0 + v0t + 1/2*at^2)
delta x = V0*(t)
delta y = 1/2gt^2
what is the optimal angle for a launch? is this the absolute best angle? why or why not?
45 degrees ONLY on level terrain. a cliff, for example, would provide extra hang time that would cause a higher horizontal velocity to be of more benefit
kinematic equations vs. stuff like a = v/t
kinematics are used for INSTANTANEOUS values of variables, whereas the “other stuff” is used for AVERAGES (a(avg) = delta v / delta t)
tldr;
instantaneous points in time vs. averages with CONSTANT slopes
https://www.youtube.com/watch?v=N0TngZunzXY&list=PLPyapQSxH6mZdMBSO-_YWHYJ9DpWBxiFG&index=8