physics_ОГН_10 grade_Lw 1_Learning the motion of ball in viscous fluids’_lab work

THE STUDY OF THE MOTION OF THE BALL IN FLUIDS OF DIFFERENT VISCOSITY

When a body falls in a viscous fluid, it experiences a drag force that counteracts the movement of the object. In a more viscous fluid, the bodies experience greater values of the drag force. In this experiment, you investigate how the velocity of a ball falling in a liquid depends on its viscosity.

(а) Secure the test tube in the tripod as shown, as shown in Fig.1.1.

(i) measure and write the height of the liquid h in the vial

h = ..................................................сm [1]

(b) (i) Mount the ruler vertically with the stand and clip.

(ii) Release the ball from a close distance from the liquid surface, as shown in Fig.. 1.2.

Measure and record the time t of the ball falling from height h.                                                                              [2]

h = ..................................................сm

t = .....................................................s

(с) Calculate the percentage error for the time of the fall of the three balls,                                                        [3]

ε_t = .......................................................

(percentage error)

(d) Calculate the average speed of the ball                                                                                                       [2]

v = .............................................сm×s^-1

(е) (i) change your test tube to a test tube with another liquid.

(ii) Repeat steps (b)(ii) и (d), record your results.                                                                                        [2]

h = ..................................................сm

t = .....................................................s

v = ............................................. сm×s^-1

(f) It is assumed that the velocity of the ball V is inversely proportional to the viscosity. Do the results of the experiment confirm this assumption? Explain your reasoning.                                                                               [2]

..........................................................................................................................................

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(g) (i) Write what could be possible errors or limitations in the procedure in this experiment.                             [4]

1. ...............................................................................................................................

2. ...............................................................................................................................

3. ...............................................................................................................................

4. ...............................................................................................................................

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(ii) Suggest 4 improvements (solutions to these difficulties or errors). You can suggest using other equipment or other actions.                                                                                                                                                          [4]

1. ...............................................................................................................................

2. ...............................................................................................................................

3. ...............................................................................................................................

4. ...............................................................................................................................

Mark scheme

Manipulation, measurement and observation

Successful data collection

(а) (i) First h in cm or mm.                                                                                                               [1]

(b) (ii) The first value is t (must be between 0.1 and 10 seconds).                                                  [1]

(с) (ii) The second value of h (should be approximately equal to the first)                                    [1]

(е) (ii) The second value of t (less than the first).                                                                           [1]

(е) (ii) Several time measurements in each liquid                                                                           [1]

(е) (ii) Repeated measurements for t (first or second measurement)                                               [1]

Data quality

(g) (ii) High viscosity gives less speed or V (use corrected values of V).                                       [1]

Presentation of data and observations

The submission of calculation and reasoning

(d) The first value of V is calculated correctly. Calculations should be checked (if not, write in the correct value).                                                                                                                                               [1]

(е) (ii) The second value V is calculated correctly. Calculations should be checked (if not, write the correct value).                                                                                                                                               [1]

(с) The correct calculation to check proportionality                                                                        [1]

The analysis, conclusions and evaluation

Ability to draw conclusions

(f) Conclusion                                                                                                                                   [1]

Sensible comments relating to proportionality calculations and to the suggested relation. Incorrect ideas score zero.

Uncertainty estimates

(с) the uncertainty in percent for the t.                                                                                             [1]

Absolute uncertainty should be between 0.1 and 0.5 s, or if repeated readings have been made then uncertainty can be half the range.

It is necessary to Express uncertainty in percent.

Constraint definition

(g) (i) The corresponding points should be underlined and ticked.                                                 [4]

Some of them may be:

A.     And Two sets of readings are not enough to determine the pattern.

B.     In the Ball may not reach the speed limit. (hover)

C.     With hardly time to see the impact of the ball on the bottom.

D.     Human error in timing / reaction time.

E.      Parallax (when reading positions).

F.      Other reasonable source of error

Assuming improvements

(g) (ii) The corresponding points should be underlined or ticked.                                                  [4]

Some of them may be:

A.    Take more value sets and plot / calculate coefficients.

B.     Verify the speed limit by increasing the altitude / measurement speed value in two intervals to check the speed limit.

C.     Use the video to slow down when the ball lands.

D.    Measuring the time of fall from a greater distance.

E.     Drop in front of a ruler / read at eye level.

F.     Another improvement, well explained.

Not to take: re-reading '(if not used ' graph ').

Do not take: 'use a computer to improve the experiment "