7.7(D): Analyze the effect of balanced and unbalanced forces on the state of…

Forces and Motion: Crash, Push and Stop Grade 8

Why you lurch forward when the bus brakes, how fast a toy car really goes, why heavier carts hit harder, and how to build a crumple zone that saves an egg. Four lessons on inertia, speed, mass and stopping safely.

• Why do you lurch forward when a bus stops? 50–60 min

  Students flick a card out from under a coin, then crash toy cars carrying loose clay passengers into a barrier and measure how far the passenger flies. They use their data to explain inertia and to design a better seatbelt.

• How fast is a toy car really going? 50–60 min

  Teams time a toy car over measured distances from two ramp heights, calculate its speed and draw distance-time graphs. They use the slope of their graphs to argue which run was faster, and convert a toy car's speed to a real car's.

• Why does a heavier cart hit harder? 50–60 min

  Teams load a toy car with coins, roll it down the same ramp into a paper cup and measure how far the cup slides. They graph mass against slide distance and explain, with momentum, why a loaded truck is harder to stop than a small car.

• Can you design a crumple zone? Two periods of 45–60 min (or one 75–90 min block)

  Teams design, build and test a crumple zone that lets a raw egg in a zip bag survive a cart crash into a wall, working to a budget and a size limit. They measure how far each design crushed and use class data to explain why a longer stop means a smaller force.

Printable practice for 7.7(D)

• Forces and Motion: Crash, Push and Stop workbook included with the unit

  3 practice pages, 3 readings, 2 English-support pages, 1 word wall, 1 unit review, 1 unit test, with answer keys.

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