Junior School Forces and Motion Investigation

Forces and motion investigation: compare rolling records fairly

How does the surface covering affect the distance a toy trolley rolls before stopping? This junior-school investigation is a paper task built around simulated records. You will check the comparison, calculate means, choose a suitable graph and distinguish a measured distance from an explanation about forces. No trolley, ramp or physical experiment is required.

The completed investigation plan

The fictional trolley enters a marked horizontal test section at the same supplied speed, 0.30 m/s, in every trial. It then rolls freely without further pushing. The independent variable is the surface covering: smooth board, card or fabric. The dependent variable is the distance travelled from the entry line until it stops, recorded in centimetres.

Use the same trolley, load, wheels, horizontal path and stopping rule in every comparison. The record defines entry and stopping position using the front axle, so one reading does not start at the front bumper while another ends at the back wheel. The supplied equal incoming speed is important: an uncontrolled harder push could increase distance independently of the covering.

Three trials are supplied for each covering. The model also assumes the surface is in the same condition at each repeat. A physical classroom version would need a separate teacher risk assessment, a low-speed contained level path and secure stopping arrangements. This lesson does not ask learners to use heights, launch objects or work near traffic or powered machinery.

Completed simulated rolling-distance record

For card, mean distance = (50 + 52 + 51) ÷ 3 = 153 ÷ 3 = 51 cm. Range = 52 − 50 = 2 cm. The smooth-board mean is 225 ÷ 3 = 75 cm. The fabric mean is 87 ÷ 3 = 29 cm. Smooth board exceeds card by 24 cm and fabric by 46 cm. These are comparisons of this simulated record.

Choose a comparison graph

Use a bar chart because the horizontal categories are surface coverings. Label the horizontal axis “Surface covering” and the vertical axis “Mean rolling distance (cm)”. Start the distance scale at zero, use equal numerical intervals and draw separate equal-width bars reaching 75, 51 and 29 cm. The data table is the complete nonvisual alternative.

Do not join the tops of these bars and call the result a distance-time graph. No times for the journey were recorded, and moving from one category to the next is not the trolley moving through space. A gradient from this chart would not give speed. This distinction uses the same axis-reading habit needed for distance-time and velocity-time graphs, without requiring their more advanced calculations.

An observation, an interpretation and a limit

Observation: the mean stopping distance is greatest on smooth board and smallest on fabric. Interpretation: with the stated incoming motion and controls, the pattern is consistent with different resistive effects associated with the coverings. Limit: the record does not measure a force in newtons or identify exactly which mechanism accounts for every difference.

The trolley and surface can interact through rolling resistance, wheel deformation and other effects. “Fabric produced exactly twice the friction” is unsupported by these distances. Neither the mass nor a complete motion history is given for calculating a force, and stopping distance is not itself a force reading. A careful explanation can mention resistance without pretending to have measured it.

The three ranges are small compared with the differences between these means. That supports a clear pattern within this constructed dataset, but three repeats are not a guarantee about every trolley or surface. Do not report an exact best material for all settings or claim that the trolley had constant speed while it was stopping.

Independent check

1. A new covering gives simulated distances of 40, 42 and 44 cm. Find its mean and range. Convert the mean to metres.
2. A second learner uses a heavier trolley on fabric and a lighter trolley on board. Why is this no longer the same comparison? Give a repair.
3. Someone says the smooth-board mean of 75 cm means the trolley travelled at 75 cm/s. Explain the missing evidence.
4. Choose the better conclusion: “The data support a longer mean roll on board under these conditions” or “Board always has no friction.” Explain your choice.

Answers and learning rubric: 10 marks

1. Mean = (40 + 42 + 44) ÷ 3 = 42 cm; range = 44 − 40 = 4 cm; mean = 0.42 m. Award 1 mark for each correct value and unit: 3 marks.
2. Mass/load changed together with covering, so the comparison cannot isolate covering: 1 mark. Use the same trolley and load and retain comparable incoming speed: 1 mark. Preserve the other stated measuring conditions: 1 mark.
3. 75 cm is a distance: 1 mark. Average speed needs a measured elapsed time for that distance; this record does not supply it: 1 mark.
4. The first conclusion is supported because it refers to the supplied comparison: 1 mark. The second is an unsupported universal claim, and distance alone does not establish zero friction: 1 mark.

Before finishing, check units in every heading, keep raw readings beside the means and underline the condition limiting your conclusion. If you changed a value while calculating, restore the original reading and show the correction separately. The purpose is a traceable argument from records to conclusion, not a graph that merely looks tidy.

Background: OpenStax: speed and velocity. The stopping-distance dataset, categorical chart and questions here are original.

More junior-school revision

For broader navigation, use the junior-school resource collection or the Grade 9 topical resource index. Check individual access conditions and contents; this lesson does not verify a particular member file or an exact current grade/term allocation.