| Date | November 2021 | Marks available | 3 | Reference code | 21N.2.HL:.tz0.2 |
| Level | Higher Level | Paper | Paper 2 | Time zone | time zone 0 |
| Command term | Comment | Question number | 2 | Adapted from | N/A |
Question
A separate study examined the performance of four grip-enhancing agents (chalk, rosin, liquid chalk, Venice turpentine) used in sports like weightlifting and climbing. Grip effectiveness was measured in four different conditions:
- Condition 1: Dry fingers, dry surface (control)
- Condition 2: Damp fingers, dry surface
- Condition 3: Wet fingers, dry surface
- Condition 4: Dry fingers, wet surface
Figure 1: Coefficient of friction for the grip-enhancing agents in the four conditions
[Source: Carré, M. J., Tomlinson, S. E., Collins, J. W. and Lewis, R., 2012. An assessment of the performance of gripenhancing
agents used in sports applications. Proceedings of the Institution of Mechanical Engineers, Part J: Journal
of Engineering Tribology, 226(7), pp. 616–625. Copyright © 2012 by SAGE Publications. Reprinted by Permission of
SAGE Publications. Source adapted.]
Identify the grip-enhancing agent with the greatest coefficient of friction in Condition 3.
Using the data in Figure 1, analyse the influence of Venice turpentine on grip.
Comment on the meaning of the standard deviation, with reference to the data in Figure 1.
Describe the effect of different materials on the coefficient of friction.
Markscheme
chalk;
Condition 1:
Venice turpentine in dry finger–dry surface/Condition 1 has the greatest grip/coefficient of friction/greatest grip effectiveness;
Condition 2:
Venice turpentine in damp finger–dry surface/ Condition 2 has the greatest grip/coefficient of friction/greatest grip effectiveness;
Condition 3:
in wet environment/wet finger and dry surface/Condition 3, Venice turpentine yields lowest coefficient of friction/is the worst enhancing agent
OR
Venice turpentine yields the lowest overall coefficient of friction/has the poorest overall grip effectiveness;
Condition 4:
in wet environment/dry finger and wet surface/Condition 4, Venice turpentine yields lowest coefficient of friction/is the worst enhancing agent;
a small SD small standard deviation indicates that the data is clustered around the mean e.g. bars on most conditions/ liquid chalk in condition 3
OR
a higher SD e.g. Venice turpentine in any condition/liquid chalk in condition 2/Rosin in condition 3 indicates that the
data is <more> spread from the mean;
a smaller standard deviation can indicate greater reliability of the data;
chalk has a relatively small standard deviation in all conditions which suggests that there is little variation in performance using this agent;
Venice turpentine has a relatively large standard deviation in all conditions which suggests that there is a more significant variation in performance using this agent;
Award [1 max] if there is no reference to data.
Accept answer that refers to relative proportion of the SD to mean.
Accept in the converse.
Note: statistical significance cannot be determined from the data.
the coefficient of friction (COF, μ) is < a dimensionless scalar quantity which is > the ratio of < the force of > friction < Ff between two bodies > and the normal reaction force <R>
OR
;
the magnitude of the coefficient of friction depends on the materials in contact;
the greater the interaction between the molecules of the interfacing surfaces/more rough the surfaces, the greater the size of the coefficient of friction;
Accept any appropriate examples.
Note on mp2: must say something more than repeating the question, e.g. give an appropriate example.
Accept in the converse.
Must have reference to effect of the surface on the coefficient of friction.
Examiners report
Most candidates answered well, although not all candidates attempted these parts of the question.
Most candidates answered well, although not all candidates attempted these parts of the question.
Many candidates were able to outline what the error bars represent and relate it to the data. However, many candidates simply outlined the converse. Very few candidates achieved more than two of the three marks on offer.
Many candidates struggled with this question with most repeating their response from 2b. The most common correct response was 'the greater the interaction between the molecules of the interfacing surfaces/more rough the surfaces, the greater the size of the coefficient of friction'.
