Lesson 2 of 12 · Forces
Experiment⭐ 30 XP⚡ Spark LabNewton's Second Law: F = ma
Newton's Second Law: F = ma.
🎯 Your mission
Set it up. Test it. Be amazed.
⚡ The twist
Energy never disappears — it just hides somewhere else.
Mind = Blown
🎢 You feel weightless on a roller coaster because you and the seat are falling at the same speed.
Make a hypothesis first
Before you start: which will move faster, and why?
What You'll Learn
The resultant force on an object equals its mass times its acceleration. Doubling the force doubles the acceleration; doubling the mass halves it. Force is measured in newtons, where one newton accelerates one kilogram at one metre per second squared.
Key Words
Tap a word to see its definition.
Materials Needed
- dynamics trolley or toy car
- spring balance
- masses
- stopwatch
- metre rule
Safety First
- Keep fingers clear of the trolley's path and stop it at the bench edge.
Steps
Read the explanation above and note the two key terms before you start.
Pull a trolley along a bench with a spring balance held at a constant reading and time it over a metre. Repeat at double the force, then repeat at the original force with a second mass on board. Tabulate force, mass and acceleration.
Record what actually happened, including anything that did not match what you expected.
Write a conclusion that answers the question this lesson opened with, and state your uncertainty.
Check Your Understanding
Question 1
1 of 2A 4 kg object accelerates at 3 m/s². The resultant force is:
Where you see this in real life
You use this every time you flip a light switch, ride a bike, or kick a ball.
Stretch Challenge
Try this in real life this week.
Time how long a small ball rolls down something, then change the slope and try again.
For the dinner table
“Show me something at home that uses this kind of energy.”
Next Smart Experiment
We'll pick an experiment that matches exactly how you're thinking right now.
Share this experiment
Send it to a parent who's looking for a 10-minute kitchen science win.
Ready?
Newton's Second Law: F = ma
Set it up. Test it. Be amazed.
Full screen — no distractions
Checkout complete lesson on Forces for 9th Grade
Get the full Forces track as a printable PDF — all lessons, worksheets, and answer keys.