Paper Car Crash

Crashworthiness by Design

A Thought Experiment

Imagine you trip and fall.

Scenario A: You land on a concrete sidewalk.

Scenario B: You land on soft sand.

Which one hurts more? Why?

Same Impulse, Different Force

In both cases, your momentum changes by the same amount — you go from moving to stopped.

But the time over which you stop is very different.

  • Concrete: you stop fast → large force
  • Sand: you stop slowly → small force

The sand "gives" during the collision, spreading the force over a longer time.

The Impulse–Momentum Theorem

The change in momentum equals the average force multiplied by the time the force acts.

If the impulse () is the same, then:

  • Short time → large force
  • Long time → small force

How Do Real Cars Use This?

Vehicle engineers face the same physics.

A car going 60 mph has a lot of momentum. In a crash, that momentum drops to zero.

Engineers can't change the impulse — but they can change the time.

Crumple Zones

The front of a car is designed to collapse on impact.

As the front end crumples, the car takes longer to stop.

Longer stopping time → smaller average force on the passenger compartment.

The Safety Cage

Behind the crumple zone, the passenger compartment is built to be rigid and strong.

This is the safety cage — it's designed to keep its shape even when the front and rear of the car are destroyed.

The crumple zone absorbs energy. The safety cage protects the people inside.

Seat Belts

During a crash, the car stops — but you keep moving (inertia).

A seat belt connects you to the safety cage so you slow down with the car instead of slamming into the dashboard or windshield.

Without a seat belt, your body experiences its own separate collision — at full speed, against something hard.

Putting It All Together

A crashworthy car has three things working together:

  1. Crumple zone — increases stopping time, reduces force
  2. Safety cage — rigid compartment that holds its shape
  3. Seat belt — keeps the occupant attached to the cage

If any one of these fails, the occupant is in trouble.

Your Challenge

Design and build a paper car that protects a raw egg during a head-on collision with a concrete block.

Your car will roll down a ramp and crash into a wall.

The egg must survive.

The Rules

  • Materials: 2 sheets of copy paper, tape (masking or scotch), and teacher-provided wheels, axles, and straw housing
  • Your car must fit inside the gutter ramp and roll freely
  • Minimum mass (without egg): 40 g
  • No cardboard, stickers, or paint
  • The straw can only be cut up and used as axle housing
  • The egg must be easy to remove for inspection after each crash

Design Questions to Consider

Before you start building, think about these:

  • Should the front of your car be rigid or should it collapse on impact?
  • Should the egg sit loosely in the car, or be secured in place?
  • How do you make the front weak enough to crumple but the passenger area strong enough to survive?

The Competition

Winner has the largest momentum and a Safe egg!

What You'll Calculate

Before the competition, you will:

  • Measure your car's mass and the track distance
  • Time a practice run to find average velocity
  • Calculate your car's momentum at impact

The Timeline

Day 1 — Brainstorm and build

  • Sketch at least two different designs before you start
  • Build your car

Day 2 — Build and Test measurements

  • Measure mass, check specs
  • Practice runs (no egg, no wall)
  • Crash competition with eggs

Day 3 — Crash 💥 & Analysis =

Before You Start

✅ Read over lab handout

✅ Two sketches in your notebook first — then build.

✅ Think about the physics. Every design choice should connect back to impulse, momentum, and force.

✅ Go!