Viscous
Up thrust drag
(u) (f)
Weight (w)
If by any chance the acceleration period is too long then I could reduce the size of the ball bearing so it reaches terminal velocity quicker
The left tube is too small and the ball bearing will not move through the honey because there is no way for the honey to get round the ball bearing. The middle tube is wider which means the ball bearing will fall through the honey but not as fast as it would in the tube to the right. This is because of the way the liquid travels. At the sides of the tube the liquid travels at a very slow speed because it has a stationary object next to it, as you move inwards the liquid travels a bit faster because it hasn’t got a stationary object next to it but a slow moving liquid, this means the liquid inside that can move even quicker until you get to the middle, and that is where the fastest liquid travels. Look at the diagram below for a better understanding:
Slow moving
Liquid
Fast moving
Liquid
= Velocity gradient
An example of this velocity gradient is in a river, when you try to cross a river the slowest moving water is at the edge, as you make your way across the river the water current gets faster and is fastest in the middle, when you pass the middle the water starts to get slower moving again.
To calculate the unit for viscosity:
F = A V/d L = Length
T = Time
ML/T² = L² L/T/L M = Mass
ML/T² = L² L / T / L
ML/T² = L²/T
L²/T = ML/T²
= (ML/T²)(T/L²)
= M/TL
Unit ML ¹ T ¹
For formula use, length is measured in metres, time in seconds and mass in kilograms, so the unit for viscosity is – kg m ¹ s ¹
This diagram shows the content of particles within the honey. Each particle has a force and is moving about colliding with other particles. As thermal energy is supplied to increase the temperature, the energy is shared out between the particles increasing the kinetic energy on each particle. If a ball bearing was to be dropped in honey at a lower temperature then it would fall slower because of the slower moving particles not moving out of its way. If you drop the ball bearing into warmer honey it will fall faster because the particles will move out of the way faster.
Method:
- Set up equipment as in diagram, with water bath at room temperature.
- Fill up plastic tube with honey above the mark of timed distance to give the ball bearing a chance to accelerate.
- Mark on the 7cm timed distance; it has to be below the water line so that all the honey is at the same temperature, not just the bottom bit.
- Drop the ball bearing into the honey tube.
- Start the stopwatch when the ball bearing reaches the first timed distance mark, and stop the stopwatch when it reaches the second timed distance mark.
- Repeat this three times for the same temperature to get reliability.
- Heat the water around the honey by 10°c
- Repeat steps 4-7 until the water around the honey has reached 60°c.
- Measure all the ball bearings used with a venire calibre.
Results:
Evaluation:
Percentage errors:
Venire Calibre (diameter of ball bearing)
0.005/3 x 100 = 0.166%
This percentage error is very small and so will not affect my results.
Ruler (distance travelled)
0.05/7 x 100 = 0.71429%
This is again very small so my results will still be quite accurate.
The whole experiment is reliant on Newtonian physics. This means that the ball bearing will have to fall through the honey in a straight line, any variation to this would cause inaccuracies in my results.
Conclusion:
My results show the viscosity of honey is proportional to temperature. A variable that could have affected my results was the density of the honey but the volume of honey only raised by 1mm showing that the density change was not enough to account for the change in viscosity.
