IB Physics SL S2.1 Exploring and Designing Questions

Practise IB Physics SL S2.1 by turning a physics question into a testable plan with variables, controls, apparatus and safety.

Exam points

formulate or identify a research question, hypothesis, variables and a reproducible investigation method
select and justify controlled variables, ranges, repeated measurements, sampling or practical improvements
explain how a designed investigation can manage risk and produce data suitable for assessing the hypothesis

Covered syllabus points

S2.1.1—Exploring S2.1.2—Designing investigations S2.1.3—Controlling variables

[Maximum number: 1]

A student studies the relationship between the centripetal force applied to an object undergoing circular motion and its period T.
The object (mass m ) is attached by a light inextensible string, through a tube, to a weight W which hangs vertically. The string is free to move through the tube. A student swings the mass in a horizontal, circular path, adjusting the period T of the motion until the radius r is constant. The radius of the circle and the mass of the object are measured and remain constant for the entire experiment.

The student collects the measurements of T five times, for weight W. The weight is then doubled ( 2 W ) and the data collection repeated. Then it is repeated with 3 W and 4 W. The results are expected to support the relationship

W=\frac{4 \pi^{2} m r}{T^{2}}

State why the experiment is repeated with different values of W.

In reality, there is friction in the system, so in this case W is less than the total centripetal force in the system. A suitable graph is plotted to determine the value of m r experimentally. The value of m r was also calculated directly from the measured values of m and r.

In order to draw a graph« of W versus $\frac{1}{\mathrm{~T}^{2}}$ »

OR

to confirm proportionality between « W and $T^{-2}$ »

OR

to confirm relationship between « W and T »

OR

because W is the independent variable in the experiment

OWTTE.

[Maximum number: 1]

A group of students uses pressurized air to move a piston that forces a nail into a block of wood. A gauge is used to measure the pressure P of compressed air above atmospheric pressure. The nail enters the wood perpendicular to its surface.

The students use a ruler to measure the length of the nail which remains above the surface of the wood as shown. The depth of the nail inside the wood is d. All necessary length measurements are recorded using a ruler with uncertainty $\pm 1 \mathrm{~mm}$ .

The students systematically increase the pressure and calculate d.

State one variable that needs to be controlled when collecting the data.

[Maximum number: 1]

A student investigates whether the Stefan-Boltzmann law, $L=4 \pi \sigma R^{2} T^{4}$ , applies to stars.
L= luminosity of the star, in W
$\sigma=$ Stefan-Boltzmann constant
R= radius of the star, in m
T= surface temperature of the star, in K
To verify the law, they obtain values from databases and manipulate the data as shown.

Suggest a possible improvement of the investigation, related to the range of the surface temperatures of the stars selected.

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Covered syllabus points

Question 1

Question 2

Question 3