4 Determine the Viscosity of a Liquid Flashcards
what safety procedures should be taken in this experiment
clean up and spillages immediately as soap is very slippery and could lead to people falling
why is the experiment invalid if the diameter of the tube is too small
stokes law is only valid for laminar flow. if the tube is too narrow then the flow will not be laminar throughout
why shouldn’t light gates be used in this experiment
light gates require a clear breakage of the beam. this is unlikely in this experiment since the ball may not but the beam. the line of the beam may also be disturbed by the coloured liquid
why may the flow become non-laminar if the ball approaches the walls of the tube
if the ball approaches the fall the surrounding liquid will accelerate upwards around it due to Bernoullis principle. faster fluid flow means a lower pressure, which would further guide the ball towards the wall. as a result the stream lines would be non-symmetrical and so would be non-laminar
what forces act on a ball as it sinks down a tube of liquid
the downwards force of weight and the upwards forces of drag and upthrust
how can the uncertainty of r^2 be determined from the uncertainty of r
it would be double the uncertainty of r
how can the radius of a small ball be measured
a micrometer can be used
describe the forces on the ball when it reaches terminal velocity
the downwards forces of the ball equal the upwards forces
how should you take time readings in this experiment
at eye level to rubber bands wrapped around the measuring cylinder at set values. the lap function should be used as the ball passes past each band
what must be the case when positioning the highest rubber band on the tube
the ball should be travelling at terminal velocity by the time it reaches the first band. this means it needs to be placed low enough for this to be the case
how can you ensure that the time readings are accurate
the same person should record the time readings throughout. they should measure at eye level to the rubber bands and must ensure that they stop the timer at the same relative position between the ball and timer each time
why is it advantageous to use a steel ball bearing in this experiment
they are magnetic and so a magnet can be used to lift the balls out of the liquid at the end of the experiment
if the ball has reached terminal velocity by the time it reaches the first band what should be true about the speed calculated
the two speeds should be the same as acceleration should not exceed terminal velocity
how should the lower two bands be positioned on the tube
the two bands should be sufficiently far apart so that the time intervals between each easily observable and measurable
what equation is used to calculate the liquids viscosity
n=2r^2g(p1-p2)/9v
