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Physics 20: Kinematics

Terms in this set (33)

two types of kinematics
- linear (1D)
- planar (2D)
frame of reference
- compared to what? depending on what?
- what are you valid gesso?
- stick with same frame of reference in question
- must account for frames of reference in all scenarios
inertial frame of reference
holds still, observes
noninertial frame of reference
moving, in a moving capsule
i.e. capsule moving at 100km/h going forward, approaching object at 110km/h from front = like earth is moving with object on it = 210km/h, think of watching a movie
kinematics
- study and description of motion
- uses distance and time to describe
kinematics variables
- distance/displacement
- initial speed/velocity
- final speed/velocity
- acceleration
- time
scalar
magnitude only
vector
magnitude and direction
distance
- scalar
- d
- units: metres/m
- path dependant
- corresponding to displacement
displacement
- d with arrow on top
- vector
- units: metres/m
- path independent; where you start vs where you finish
- change in position based on reference point
- corresponding to distance
time
- scalar
- no corresponding vector - only a scalar
- units: seconds
- t
initial speed
- Vi
- scalar
- units: m/s
- corresponding to initial velocity
final speed
- Vf
- scalar
- units: m/s
- corresponding to final velocity
initial velocity
- Vi with arrow on top
- units: m/d
- vector
- corresponding to initial speed
final velocity
- Vf with arrow on top
= units: m/s
- vector
- corresponding to final speed
acceleration
- a with arrow on top
- vector - only vector, no corresponding scalar
- units: m/s2
usually, in a kinematics problem
3 out of the 5 variables are given and you solve for the unknowns
average speed formula
total distance divided by total time
Vave = change in d/change in time
- can be displacement or distance
- rate at which an object is moving
- overall mean, if same distance travelled but constant speed
acceleration formula
- a= vf - vi/t
- change in velocity over change in time
- rate at which objects speed/velocity is increasing/decreasing
- every second, speed/velocity changes by _____m/s
uniform motion
motion which involves constant speed or constant velocity
- always the same - unrealistic
non-uniform motion
motion which involves a change in speed or velocity
average speed
while variations in speed may occur, we can calculate an average speed for the time interval
instantaneous speed
speed of an object at a given instant in time
- calculated through drawing a tangent line (line that touches a curve at only 1 point) which represents the slope of the curve at that specific point, and calculating the slope of that tangent line
note on unit conversion
- converting a unit square needs to take into account the 2 dimensions (etc with 3,... dimensions, cubed...)
i.e. meters squared into centimetres squared = x 100 for 1st m, then x 100 again for 2nd m
THE equations!!!!
1. a = vf - vi/change in time (no distance)
2. d = vit + 1/2at2 (no vf)
3. vf2 = vi2 + 2ad (no time)
see notebook for many graphs and use worksheets
way to interpret motion
slope/area memory device
draw it out
----slope----->
d v a
<-------area----
velocity and acceleration in the same direction =
speeding up
- velocity up, acceleration up = speeding up!
- velocity down, acceleration down = speeding up!
velocity and acceleration in different directions =
slowing down
- velocity up, acceleration down = velocity slows, stops, and accelerates down!
- velocity down, acceleration up = velocity slows, stops, and accelerates up!
steeper slope of a v vs t graph
= higher velocity, more distance in less time
flatter slope of a v vs t graph
= lower velocity, less distance in less time
although the word deceleration describes an object slowing down
it is NOT a proper physics term!
- instead, a decrease in the velocity of an object travelling forward is called negative acceleration
- can mean taking away velocity or moving in the negative direction; either way, a v t graph representing this would have a negative slope
- can be caused by a change in speed/direction/both
what can negative acceleration mean?
1. object moving the positive direction is slowing down
2. object is accelerating in the negative direction
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