Week 4 Session: Modelling impact

A short introductory recap of the physics, then a calculator-only session turning speed, mass and two constant assumptions into numbers you can plot.

15 March 2027

Before the session#

A short lecture runs first this week, covering the kinetic-energy and stopping-distance equations and a worked example, so you have both formulas and one worked calculation before the session asks you to run the rest yourself. Bring a calculator or a laptop with a spreadsheet — no physics background and no programming are required.

The scenario#

Every calculation this week uses the same synthetic teaching scenario from the lecture:

Treat every figure above as an illustrative input, not a measured value or a safe-driving recommendation.

Calculation worksheet#

Fill in one row per speed. The formulas:

speed (m/s) = speed (km/h) ÷ 3.6 kinetic energy (J) = ½ × mass × speed (m/s)² reaction distance (m) = speed (m/s) × reaction time braking distance (m) = speed (m/s)² ÷ (2 × deceleration) total stopping distance (m) = reaction distance + braking distance

In the session#

This runs as one 50-minute sequence, after the short lecture. Work in the same pairs as previous weeks.

1. 5 minutes — predict. You already know from the lecture that doubling speed quadruples kinetic energy, so this prediction asks a different question: at 80 km/h, what happens to total stopping distance if reaction time increases from 1.5 to 2.0 seconds while braking deceleration stays unchanged? Write one sentence predicting the direction of the change (longer or shorter) and one approximate size (a guess in metres). Only once you’ve written both, check yourself with one quick line of arithmetic — braking distance doesn’t change, so the whole answer is just the extra reaction distance: 80 km/h in m/s (22.2) × the 0.5 s increase. How close was your guess?
2. 10 minutes — convert and calculate energy. Convert all three scenario speeds to metres per second, then calculate kinetic energy for each using the 1,500 kg mass. Fill in the first three columns of the worksheet above.
3. 10 minutes — stopping distance. Calculate reaction distance, braking distance and total stopping distance for each speed, using the stated assumptions. Fill in the remaining columns.
4. 10 minutes — plot. Produce two simple graphs from your six numbers: speed against kinetic energy, and speed against total stopping distance. Graph paper, a spreadsheet chart, or a careful hand-drawn plot are all acceptable.
5. 10 minutes — change one assumption. Pick either reaction time or deceleration and change it to a different, clearly stated value (for example, a 2.0 s reaction time for a distracted driver, or a = 5.0 m/s² for a wet road). Recalculate total stopping distance at all three speeds and compare the two sets of results.
6. 5 minutes — explain. In plain language, with no equations, write one sentence explaining one result from your worksheet, and one sentence naming a limitation of the model you just used.

Afterwards#

This session’s output is the Physics Does Not Negotiate Worksheet — a one-page pair submission. It’s formative and ungraded: it’s practice at running a simplified model and stating its limits, not a mark on your arithmetic. It does not introduce any new assessed requirement of its own.

The Physics Does Not Negotiate Worksheet

• Your stated assumptions (mass, reaction time, deceleration — including whichever one you changed in step 5).
• Your full worksheet, all six calculations, with units shown at every step.
• Your two graphs (speed against energy, speed against stopping distance).
• One written comparison between two of the three speeds (for example, what changed and by how much between 40 and 80 km/h).
• Two limitations of the model, in plain language — drawn from the lecture’s list or one you noticed yourself.

Keep your worksheet. It’s a rehearsal for the kind of quantitative reasoning the week 6 assignment expects you to show your working for.