ch 2 - accelerated motion Flashcards
what is acceleration?
- the rate of change of velocity of an object
- accelerating object = object with increasing speed
- unit = m s-2
- vector quantity
- gradient of velocity-time graph (straight line = constant, chnaging slope = changing acceleration)
a = v-u / t
velocity - time graph?
- gradient of velocity-time graph = acceleration (straight line = constant, changing slope = changing acceleration)
- area under graph = displacement
how to measure acceleration in the lab?
- LIGHT GATES
- from computer records time and is given length of card’s 2 interrupt sections
u = l1 / t2 - t1
v = l2 / t4 - t3
a = v - u / t3 - t1 (only gives approx. a value)
- TICKER TIMER
- for equal time intervals, find length and thus velocity
- plot graph using values - MOTION SENSOR
- computer calculates
- poor precision
what is constant acceleration/uniform acceleration?
when the change in velocity of and object is the same in the same time period
s is the symbol of?
displacement
u is the symbol of?
initial velocity
v is the symbol of?
final velocity
a is the symbol of?
acceleration
t is the symbol of?
time taken
the four equations of motion can only be used for?
- straight line motion
- an object with constant acceleration
how to derive equation 1 of the equations of motion?
a = (v - u) / t
v = u + at
how to derive equation 2 of the equations of motion?
avg. velocity = (u+v) / 2
displacement = avg. velocity * time taken
s = (u+v) / 2 * t
how to derive equation 3 of the equations of motion?
from: v = u + at, s = (u+v) / 2 * t
s= (u + u + at) / 2 * t
s = ut + 0.5at²
how to derive equation 4 of the equations of motion?
from: v = u + at, s = (u+v) / 2 * t
s = (u+v) / 2 * (v-u) / a
2as = (v+u) (v-u)
v² = u² + 2as
what are the equations of motion?
i. v = u + at
ii. s = (u+v) / 2 * t
iii. s = ut + 0.5at²
iv. v² = u² + 2as
what non-uniform acceleration?
when the velocity of an object changes by different amounts of the same time period (has changing gradient)
non uniform acceleration in a graph?
- mark point on graph, draw tangent, find gradient
what is free fall?
when an object accelerated due to gravity in the absence of any ither forces such as air resistance
symbol = g
value = 9.81 m s-2
what are the lab experiments to find g?
- ELECTORNIC TIMER, STEEL BALL, ELECTROMAGNET
- current is switched off
- ball falls and timer is automatically recorded
- measure height h
- use s = ut + 0.5at²
- take several reading and plot graph
BUT
- em retains magnetism and slows ball’s fall, so t is too big
- error in measuring height - TICKER TIMER
- weight falls and pulls tape throught timer
- increasing gap between dots shows acceleration
BUT
- friction slows weight fall - LIGHT GATE
- drop plate through light gate
- computer figures out
are the vertical and horizontal motion affected by each other?
no
vertical motion affected by?
weight, vertical acceleration
horizontal motion affected by?
velocity, NOT gravity
what are components?
the effect of a vector along a particular direction
for velocicty v and angle O to the x direction the components are?
x direction = v cos O
y direction = v sin O
when there is no air resistance, horizontal what and vertical what is constant
horizontal = constant velocity
vertical = constant acceleration
