Design Challenge
Design, test, and refine an egg-drop device
The Challenge: Design a device that protects a raw egg dropped from 2.0 meters. Use physics to make the egg’s stop take as long as possible.
A. The Design Cycle
B. Define the Problem
Criteria (what it must do)
The egg survives a 2.0-m drop with no cracks
The device lands within 1 m of the target
Bonus: lightest successful device
Constraints (limits)
Materials: 10 straws, 1 m of tape, 2 sheets of paper, 4 rubber bands
Total mass under 100 g (not counting the egg)
30 minutes to build
C. Use the Physics
A 60-g egg dropped 2.0 m hits the ground at about 6.3 m/s. What is its change in momentum when it stops? If your device stops it in 0.050 s, what is the average force?
Δp = (0.060 kg)(6.3 m/s) ≈ 0.38 kg•m/s
F = 0.38 N•s0.050 s ≈ 7.6 N
Compare: stopping on the floor in about 0.002 s would be about 190 N.
Increase stopping time: crushable straws, springy rubber bands, folded paper.
Lower landing speed: a paper parachute or fins add air resistance, so there’s less momentum to lose.
Spread the force: cradle the egg so no single point takes the hit.
Keep it upright: a device that tumbles may land on its weakest side.
D. Test and Record
| Trial | Design Change | Device Mass (g) | Egg Result | What We Learned |
|---|---|---|---|---|
| 1 | ||||
| 2 | ||||
| 3 |
E. Evaluate and Refine
Your egg cracked. Name two changes that would increase the stopping time.
Add more crushable material (straws or folded paper) below the egg; suspend the egg with rubber bands so it can move and slow gradually.
Two designs both protect the egg. One weighs 40 g and one weighs 90 g. Which is the better design, and why?
The 40-g design — it meets the criteria while using fewer materials. Engineers look for designs that meet the criteria within the constraints at the lowest cost.
How is your design like a real car safety system?
Crushable straws act like a crumple zone; the rubber-band cradle acts like a seat belt; a paper cushion acts like an airbag. All increase stopping time to reduce the force.
Check Your Understanding
5 quick questions — pick an answer to see if you’re right.
1. In engineering, a constraint is
2. Which change would best reduce the force on the egg?
3. A parachute protects the egg mainly by
4. After a failed test, engineers should
5. A 0.060-kg egg moving at 5.0 m/s stops in 0.030 s. The average force is