HS-PS2-1: Showing That Net Force Equals Mass Times Acceleration
Also called NGSS HS-PS2-1 · Topic: Forces and Interactions · Physical Science
The Official Wording
Analyze data to support the claim that Newton’s second law of motion describes the mathematical relationship among the net force on a macroscopic object, its mass, and its acceleration.
Clarification statement: Examples of data could include tables or graphs of position or velocity as a function of time for objects subject to a net unbalanced force, such as a falling object, an object sliding down a ramp, or a moving object being pulled by a constant force.
Assessment boundary: Assessment is limited to one-dimensional motion and to macroscopic objects moving at non-relativistic speeds.
NGSS Lead States, 2013 · Read it on nextgenscience.org · checked October 15, 2026
What HS-PS2-1 Means in Plain English
High school students analyze motion data, such as velocity against time graphs for a falling ball or a pulled cart, to back the claim that net force equals mass times acceleration. They find acceleration from the data and check whether force divided by mass predicts it.
Motion stays in a straight line, with everyday objects at everyday speeds, so no relativity. It builds on middle school work relating force, mass and motion (MS-PS2-2) and sets up momentum and collisions in HS-PS2-2.
HS-PS2-1 I Can Statements
- I can find acceleration from the slope of a velocity graph.
- I can show that the same force gives a heavier object less acceleration.
- I can use F = ma to predict an acceleration.
HS-PS2-1 Worked Example
A lab with a battery fan cart, whose fan pushes with a steady force, and a motion sensor.
With the same fan force, how does adding mass change a cart's acceleration?
Set It Up: A fan cart on a level track, 250 g mass bars, a motion sensor with graphing software, and a balance.
- Weigh the fan cart, then measure the fan's push with a force sensor.Cart 0.50 kg, fan force 0.25 N
- Run the cart past the motion sensor and record its velocity graph.Straight line, slope 0.50 m/s²
- Add one mass bar and run it again.0.75 kg: slope about 0.33 m/s²
- Add a second bar and run it once more.1.00 kg: slope 0.25 m/s²
- Multiply each mass by its acceleration.0.25 N every time
Doubling the cart's mass halved its acceleration, and mass times acceleration equaled the fan force each time.
Why it works: Acceleration equals net force divided by mass, so the same push spread over more mass produces a smaller change in velocity each second.
Common Mistakes with HS-PS2-1
Reading the slope of a position graph as acceleration
Calling the slope of a distance-time line the acceleration
Try this: The slope of a position graph is velocity. Acceleration is the slope of the velocity graph, so check which graph you are reading.
Using one force instead of the net force
Plugging only the fan's push into F = ma with friction present
Try this: Add all forces with their directions first. Subtract friction from the push, then use that net force to predict acceleration.
Thinking a constant force means constant speed
“The fan pushes steadily, so the cart moves at one speed.”
Try this: An unbalanced constant force makes speed change steadily. Constant speed happens only when the forces on the object balance.
Where HS-PS2-1 Fits
Practice HS-PS2-1
Quick Check
- A 2.0 kg cart feels a net force of 6.0 N. What is its acceleration?
- A velocity graph is a flat horizontal line. What is the net force?
- The same push acts on an empty cart and a loaded cart. Which accelerates more?