HS-PS2-3: Designing a Device to Soften a Collision
Also called NGSS HS-PS2-3 · Topic: Forces and Interactions · Physical Science
The Official Wording
Apply science and engineering ideas to design, evaluate, and refine a device that minimizes the force on a macroscopic object during a collision.
Clarification statement: Examples of evaluation and refinement could include determining the success of the device at protecting an object from damage and modifying the design to improve it. Examples of a device could include a football helmet or a parachute.
Assessment boundary: Assessment is limited to qualitative evaluations and/or algebraic manipulations.
NGSS Lead States, 2013 · Read it on nextgenscience.org · checked October 15, 2026
What HS-PS2-3 Means in Plain English
High school students act as engineers. They design, test and improve a device, like a helmet liner or crumple zone, that lowers the force on an object in a collision. They explain the design with physics: stretching out the stopping time shrinks the force.
Evaluation is descriptive or uses simple algebra, without advanced modeling. The design builds on momentum from HS-PS2-2 and on middle school collision design (MS-PS2-1), and it practices the engineering cycle of HS-ETS1-2 and HS-ETS1-3.
HS-PS2-3 I Can Statements
- I can explain why a longer stopping time means a smaller force.
- I can test and compare collision designs with measured data.
- I can improve a design based on test results.
HS-PS2-3 Worked Example
A bumper design challenge where a force sensor gives each team a hard number to beat.
Which bumper design gives the smallest peak force when a cart hits a wall?
Set It Up: A lab cart released from one mark on a ramp, a force sensor fixed to a wall block, foam pads, drinking straws and tape.
- Define the goal: lowest peak force, bumper under 10 cm, cart unchanged.Criteria and limits listed
- Crash the bare cart into the sensor three times.Peak about 40 N
- Test a foam pad bumper, then a bundle of drinking straws taped end-on.Foam about 15 N, straws about 8 N
- Look at why the straws worked: they crushed gradually.Longer contact time on the graph
- Refine with longer straws and retest.About 5 N
The crushable straw bumper cut the peak force to about one eighth of the bare cart's, and a longer bundle did better still.
Why it works: The cart's change in momentum is the same in every crash, so stretching it over a longer time requires a smaller force.
Common Mistakes with HS-PS2-3
Thinking a soft bumper reduces momentum change
“The foam takes away some of the cart's momentum.”
Try this: The cart still goes from moving to stopped either way. The bumper only stretches the time, which spreads the same change over longer.
Changing the test along with the design
Releasing the straw cart from a lower mark
Try this: Keep the release point, cart and sensor identical for every trial so only the bumper design explains differences in force.
Picking a winner from one crash
Declaring foam the best after a single lucky run
Try this: Run each design several times and compare averages, then decide which to refine based on consistent results.
Where HS-PS2-3 Fits
Practice HS-PS2-3
Quick Check
- Why do cars have crumple zones that crush in a crash?
- A helmet doubles the stopping time of a head in a fall. What happens to the average force?
- Why keep the cart's release point the same for every trial?