Exercises: Preparing for the Physics in Practice Investigation

Ciara, a Fifth Year student in Tralee, wants to know how the Physics in Practice Investigation works. Decide whether each statement is true or false, and rewrite each false statement so that it is correct.

1. The Investigation is worth 40% of the Leaving Certificate Physics marks and the written examination is worth 60%.

2. Every teacher writes a different brief for their own class.

3. The State Examinations Commission (SEC) publishes an Investigation Brief every year, in term two of Year 1 of the course.

4. The Investigation is only an experiment. Students do not have to do any research.

5. Students submit a report of their investigation in Year 2, in a format prescribed by the SEC.

6. Only the final result matters. Students should not describe how the work actually unfolded.

7. The brief helps students to start an investigative log that they can draw on later.

Then answer:

1. a) Name the two kinds of work that make up the Investigation, and say which one uses secondary sources and which one produces primary data.
2. b) Ciara asks you the exact date for handing in the report and the exact format of the report. Where should she look, and why can you not simply give her a date from this exercise?

A class in Ennis is practising how to write a hypothesis. They are using a practice context (a trolley rolling down a ramp and a pendulum). It is not the real SEC brief. Here are five statements.

1. "Ramps are interesting to study."

2. "The steeper the ramp, the greater the speed of the trolley at the bottom."

3. "A heavier trolley is better."

4. "Does the length of a pendulum affect its period?"

5. "The period of a pendulum increases as its length increases, because $T = 2\pi\sqrt{l/g}$."

1. a) For each statement, say whether it is a testable hypothesis, a question, or too vague to test. Give a one-line reason.
2. b) Rewrite statement 3 as a testable hypothesis. State what you would change (independent variable) and what you would measure (dependent variable).
3. c) Which of the five statements is underpinned by physics theory? Explain.

Seán, a student at a school in Limerick, tests this hypothesis: "The steeper the ramp, the greater the speed of the trolley at the bottom." He lets a trolley roll down a $1.20\ \text{m}$ ramp and uses a light gate at the bottom to measure its speed. He changes the height of the top of the ramp.

1. a) Identify the independent variable and the dependent variable.
2. b) List at least four variables that Seán must keep constant (controlled variables). For each, say how he can keep it constant.
3. c) Name the instrument he could use to measure the height of the ramp, and give a sensible resolution for it (for example $1\ \text{mm}$).
4. d) Seán only does one run at each height. Give one reason why this is a weakness.

Orla is planning to find the specific heat capacity of an aluminium block, using a $12\ \text{V}$ immersion heater, a joulemeter (or a power supply with an ammeter and voltmeter), a thermometer and a stopwatch. Follow your school's own safety rules in any real work. For this exercise, write a short plan.

1. a) Copy and complete a risk assessment table with at least four rows. Use these headings: Hazard, Who or what could be harmed, Control measure.
2. b) Design a data table for her measurements. Include column headings with units, and say how many readings she should take and how often.
3. c) Describe two steps she could take to improve the quality of her primary data (for example, to reduce heat loss to the room).
4. d) List three things Orla should record in her investigative log while carrying out the experiment, and say why an honest record matters, including measurements that did not go to plan.

A student at a school in Kilkenny tests the hypothesis that $T^2$ is proportional to the length $l$ of a simple pendulum. For each length she timed 20 complete oscillations three times.

$l$ (m)	Time for 20 oscillations (s): trial 1	trial 2	trial 3
0.30	21.9	22.1	22.0
0.50	28.4	28.3	28.5
0.70	33.6	33.7	33.5
0.90	38.1	38.0	38.2
1.10	42.0	42.2	42.1

1. a) For each length, calculate the mean time for 20 oscillations, the period $T$, and $T^2$. Present your results in a new table, to two decimal places for $T^2$.
2. b) Describe how you would plot a graph to test the hypothesis. State which quantity goes on each axis and what shape of graph supports the hypothesis.
3. c) Use the points for $l = 0.30\ \text{m}$ and $l = 1.10\ \text{m}$ to calculate the gradient of the graph.
4. d) The theory gives $T^2 = \dfrac{4\pi^2}{g}\,l$. Use your gradient to calculate a value for $g$ and compare it with $9.81\ \text{m s}^{-2}$ using a percentage difference.
5. e) Explain why timing 20 oscillations is better than timing one.

Fionn is researching the question "Does a heat pump really save energy in an Irish home?" He finds three sources. They are invented for this exercise.

• Source A: A review article in a scientific journal, published two years ago by a team of university researchers. It has a list of references and describes how its data were collected.

• Source B: A brochure from a company that installs heat pumps. It says "saves up to 80% on heating bills" but gives no data and no references.

• Source C: An anonymous post on an online forum, with no date, saying "heat pumps never work in Ireland".

1. a) Evaluate the reliability of each source. Use at least four criteria, for example author, evidence, references, date and possible bias.
2. b) Put the sources in order from most to least reliable. Explain how Fionn could still make careful use of Source B.
3. c) The spec says that a good investigation uses a number of varied, balanced and referenced sources. Explain what balanced means here, and suggest two more types of source Fionn should look for.
4. d) Write a consistent reference for Source A (invent plausible details: authors, year, title, journal).
5. e) Self-assess your own research against this rubric and give a level and one-line evidence for each criterion.

Rubric: research with secondary sources (simplified from the descriptors of quality)

• Range of sources: High: a large number of varied, balanced and referenced sources. Moderate: a number of balanced, mostly referenced sources. Low: some referenced sources.

• Reliability: High: evaluates the reliability of the sources used. Moderate: considers the reliability of the sources. Low: little effort to consider reliability.

Aoife, a student at a school in Sligo, tests this hypothesis: "A beaker of hot water cools faster when it starts at a higher temperature." She pours $200\ \text{mL}$ of water into the same beaker each time, with no lid, in a room at $20\ ^\circ\text{C}$. She records the fall in temperature during 5 minutes. The thermometer reads to $\pm 0.5\ ^\circ\text{C}$. She did one run for each starting temperature.

Starting temperature (°C)	Excess over room temperature (°C)	Temperature fall in 5 min (°C)
80.0	60.0	11.5
70.0	50.0	9.5
60.0	40.0	7.8
50.0	30.0	5.6

1. a) Calculate the ratio (fall in temperature) / (excess over room temperature) for each row. What does it suggest?
2. b) Is the hypothesis supported? Quote the data in your answer.
3. c) Write a conclusion of about 100-150 words. It must refer to the hypothesis, use numbers from the table, and avoid claiming more than the evidence allows.
4. d) State one extra piece of evidence Aoife would need before saying the cooling is proportional to the excess temperature.
5. e) Give two reasons the data may have a bigger spread than the thermometer reading error alone.

Pádraig tries to find $g$ by dropping a steel ball from a height $h$ and timing the fall by hand with a stopwatch. Here are his data (one drop for each height).

$h$ (m)	$t$ (s)
1.00	0.45
2.00	0.64

He uses $g = \dfrac{2h}{t^2}$.

1. a) Calculate $g$ for each row, to two decimal places.
2. b) He estimates that the uncertainty from starting and stopping the stopwatch by hand is about $\pm 0.1\ \text{s}$. Calculate the percentage uncertainty in $t$ for each row, then in $g$ (remember that $t$ is squared).
3. c) Say whether this error is mainly random or systematic or both, and justify your answer. Include the effect of a person's reaction time.
4. d) Suggest two specific improvements to the design (equipment or method), and say how each one reduces the uncertainty.
5. e) Write a short reflection (3-4 sentences) on what worked and what did not work. It should give an honest account and show how the plan could be revised.

Tadhg investigated how the thickness of insulation around a beaker affects the temperature fall of $200\ \text{mL}$ of water starting at $80\ ^\circ\text{C}$ over 10 minutes. He did one run for each thickness. The thermometer reads to $\pm 0.5\ ^\circ\text{C}$. The beaker had no lid, and the room temperature drifted from $19.0\ ^\circ\text{C}$ to $20.5\ ^\circ\text{C}$ during the work.

Insulation thickness (mm)	Temperature fall in 10 min (°C)
0	14.0
5	9.5
10	7.0
15	5.5
20	4.5

This is his draft conclusion:

"Our experiment worked perfectly and proved that insulation is the best way to save energy. Nothing went wrong. Everyone should insulate their house."

1. a) Using the rubric below, give the draft a level (High, Moderate or Low) for each criterion, with one reason for each.
2. b) Rewrite the conclusion in about 120-150 words. It must (i) state what the data show with numbers, (ii) mention at least two limitations or sources of error, (iii) suggest one change to the plan, and (iv) link the outcome to a real-world issue without claiming more than the data show.
3. c) Score your own rewritten version with the same rubric and justify each level in one line.

Rubric: conclusion and reflection (simplified from the descriptors of quality; your teacher and the SEC guidelines decide how real work is marked)

• Conclusions and evidence: High: valid conclusions justified by evidence. Moderate: conclusions that relate to the hypothesis. Low: limited conclusions.

• Errors and reflection: High: evaluates the design thoroughly and gives an honest account. Moderate: identifies potential sources of error and reflects on what worked and did not work. Low: fails to identify errors, or gives an incoherent or idealised reflection.

• Relating to society: High: a considered reflection locating the outcomes within broader real-world issues. Moderate: reflects on how the outcomes relate to real-world issues. Low: limited links to real-world issues.