MS-PS2-1: Designing for Collisions with Newton's Third Law
Also called NGSS MS-PS2-1 · Topic: Forces and Interactions · Physical Science
The Official Wording
Apply Newton’s Third Law to design a solution to a problem involving the motion of two colliding objects.
Clarification statement: Examples of practical problems could include the impact of collisions between two cars, between a car and stationary objects, and between a meteor and a space vehicle.
Assessment boundary: Assessment is limited to vertical or horizontal interactions in one dimension.
NGSS Lead States, 2013 · Read it on nextgenscience.org · checked October 15, 2026
What MS-PS2-1 Means in Plain English
Middle schoolers use Newton's third law to solve a collision problem. When two objects hit, each pushes on the other with an equal force in the opposite direction. Students design something, like a bumper, that protects an object during a crash.
Collisions stay in one dimension, along a straight line, either side to side or up and down. This builds on 3-PS2-1, where balanced and unbalanced forces change motion, and leads to HS-PS2-3, where students design a device that reduces the force in a collision.
MS-PS2-1 I Can Statements
- I can explain that colliding objects push on each other equally.
- I can design a bumper that protects an object in a crash.
- I can test and improve a design using collision results.
MS-PS2-1 Worked Example
A crash-test challenge with two lab carts and a passenger made of soft clay.
Which bumper design best protects a clay passenger when one cart rams another?
Set It Up: Two lab carts, floor tape marking a straight track, a 3 cm ball of soft clay, pool noodle slices, cardboard and rubber bands.
- Press the clay onto the front of cart A and launch it with the same rubber-band snap into cart B, which waits at rest.No bumper: flat spot 18 mm wide
- Watch both carts at the moment they meet.Cart B shoots forward as cart A slows
- Tape a cardboard bumper in front of the clay and repeat three times.Cardboard: 14 mm average
- Swap in a pool noodle slice, then a noodle slice with a cardboard face.Noodle: 7 mm, noodle plus cardboard: 6 mm
- Pick the best design and note one more improvement to try.Longer squash, smaller flat spot
The noodle bumpers left the smallest flat spot, because they squashed first and spread the collision over a longer time.
Why it works: The carts push on each other with equal and opposite forces, and a soft bumper stretches the collision over more time, so the force at each instant is smaller.
Common Mistakes with MS-PS2-1
Thinking the moving object pushes harder
“The moving cart hit harder than it got hit.”
Try this: In a collision both objects push on each other with equal force. Differences in damage come from mass, materials and design.
Thinking equal forces cancel out
“The forces are equal, so nothing should move.”
Try this: The two forces act on different objects, so they do not cancel. Each one changes the motion of the object it acts on.
Running an unfair crash test
A harder launch for the noodle bumper than for cardboard
Try this: Launch the cart the same way every time and repeat each design three times so the bumper is the only thing that changes.
Where MS-PS2-1 Fits
Practice MS-PS2-1
Quick Check
- A bug hits a car windshield. Which one feels the bigger force?
- When you push off a wall on roller skates, why do you roll backward?
- Why do soft bumpers protect better than hard ones?