chapter 3 - motion Flashcards
displacement (s)
- distance moved by a body in a specified direction
- VECTOR (magnitude and direction)
- measured in metres
speed (v)
- rate of change of distance
- SCALAR
- instantaneous speed is the speed at any given instant
- average speed = distance/time
measured in m/s
measuring speed
using one light gate
- timer starts when the card breaks the light beam
- stops when the other end passes through
- computer calculates speed by dividing card length by time taken
using a motion sensor
- motion sends out a series of ultrasonic pulses
- pulses reflect from nearby objects and return to a detector
- the software provides a very precise timer to measure the time elapsed between sending and detection of the pulse
using a video camera
- need a clear view of the distance scale
- the recording can be used to measure the time take
velocity
- rate of change of displacement of a body
- velocity = change in displacement / time taken
VECTOR - constant velocity means it has equal changes in displacement in equal time intervals
- non-constant velocity means its accelerating
- measured in m/s
acceleration
-rate of change of velocity of a body
- change in velocity(v-u) / time taken
- measured in m/s^2
- VECTOR
- a body accelerates if speed changes or direction changes
- constant acceleration means = velocity changes in = time intervals
displacement time graph
- gradient = velocity
- horizontal = stationary
- positive gradient = constant velocity
- curved graph = acceleration/ decceleration
velocity time graph
- gradient = acceleration
- horizontal = constant velocity
- curved = changing acceleration
- area under = displacement
deriving suvat
- v= u +at - gradient of v/t graph
- s = 1/2(u+v)t - average v*time
- s = ut +1/2at^2 - sub v=u+at into s = (u+v )/2 t
- v^2 = u^2 +2as - sub t = (v-u)/a into v = u +at
all suvat
v = u + at
s = ut +1/2at^2
s = 1/2(u+v)t
v^2 = u^2 + 2as
g
acceleration due to gravity
g is + for falling objects
g I s- for upwards projection
how galileos experiments overturned Aristotle ideas of motion
- show that constant force is not needed to maintain motion but force is needed to start/stop/chanhe speed and direction
relationship between d and t for an object in freefall from rest
s is proportional to t^2
effect of mass on the acceleration of an object in free fall
no effect
projectiles suvat
- air resistance is negligable
- path is a parabola
- t1 = t2 (total t = 2*t1)
- Uh is constant bc aH is 0 (Uh= Vh)
VERTICAL - v = 0
- a = -9.81
HORIZONTAL - u = v
- v = u
- a = 0
projectile = object acted upon only by gravity
what angle results in max range (horizontal s)
45
stopping distance
thinking + breaking
thinking - distance taken to put on the breaks (reaction time)
TD is prop to speed
TD = speed *reaction time
breaking - distance taken for car to stop
BD is prop to speed^2
vector
scalar
size and direction
just size
vector adding ( same line)
2 vectors in the same direction add to make one big vector
vectors at right angles
use pythagorus to find the size and trig to find the angle
scale drawing vectors
- chose a suitable scale
- draw a vector to represent one
- draw the next vector with its tail starting at the tip of the first one
- the resultant vector connects the start point to the very end
- can find length / angle with rule/ protractor
finding horizontal / vertical from a resultant vector
x = F cos(θ)
y = F sin (θ)
describe how you would experimentally find the speed of a ball
how would you find acceleration of free fall (using galileos method and modern day equipment)
- set up two light gates - attached to a data logger
- roll a ball between them
- width of ball is known (d is known)
- t is recorded
- comp works out v and u using d/t and can find a using v-u/t
