our dynamic universe Flashcards
law of the conservation of energy
energy cannot be created or destroyed, just changed from one form to another
energy is the same as…
work done
constant speed in a lift
forces are balanced and tension=weight
up and accelerating or down and decelerating
forces are unbalanced and tension>weight
up and decelerating or down and accelerating
forces are unbalanced and tension<weight
momentum units
kgm/s
law of the conservation of momentum
the total momentum before is equal to the total momentum afterwards in the absence of external forces
momentum calculation
m1u1+m2u2 = m1v1+m2v2
momentum in explosions
must still be conserved, the total momentum before is 0 therefor the total momentum after must be 0
energy in collisions
total energy must always be conserved
kinetic energy in collisions
kinetic energy is only conserved in elastic collisions
energy: scalar or vector
scalar
random uncertainty
random fluctuations can effect measurements from reading to reading
systematic uncertainty
when the measurements are all affected in the same way, giving slightly incorrect values
scale reading uncertainty
indicates how well a scale can be read, for widely spaced scales, this can be a little pessimistic
random uncertainty calculation
max reading - min reading (all divided by) number of readings
analogue scale reading uncertainty calculation
+/- half of the least division of the scale
digital scale reading uncertainty calculation
+/- 1 in the least significant digit displayed
how to compare uncertainties
take the percentage of each
impulse calculation
Ft = mv-mu
impulse: scalar or vector
vector
impulse
the change in momentum
impulse units
kgm/s
momentum equation
p=mv
inelastic collisions
kinetic energy is not conserved
elastic collisions
kinetic energy is conserved (rare and only found in particles as sound and heat is usually let off)
impulse graphs
the area under a force time graph is equal to the impulse
how do crumple zones on cars protect passengers
the change in momentum can’t be changed at the time of the accident however crumpling on impact increases the time of collisions meaning the peak force is less causing less harm
scalar
only magnitude
vector
both magnitude and direction
freely under gravity
-9.8m/s/s due to gravity
area under velocity time graph
displacement
the direction of acceleration
is the direction of the unbalanced force
