Physics experiments for kids do not need a lab, just things that roll, swing and bump. The best ones ask one clear question, like "what makes it stop?", and let your child see the answer. Below are five tests from real science curricula, scaled for ages 5 to 10, plus a list of questions that grow into a science fair project.
The four big ideas behind every experiment here
DK's playground spread tags every piece of park equipment with its forces: a swing is push and pull, a slide is gravity and friction, a seesaw is balance2. You can say the same at home. NASA's physics pages give the grown-up version of the rules4:
- First law. An object in motion stays in motion at constant speed and in a straight line unless acted on by an unbalanced force4. For a 5-year-old: for something to stop, something has to get in its way3.
- Second law. How fast something speeds up depends on its mass and how hard you push4.
- Third law. When one object pushes on another, the second pushes back equally hard4.
Energy is the ability to do work, or to make something move.1
A push or a pull2.
Say it: “Did you push it or pull it?”The pull that brings things down toward the ground2.
Say it: “What happens if we let go?”The rubbing that slows things down when two surfaces slide past each other2.
Say it: “Which floor makes it stop faster?”Stored energy, waiting to turn into motion (kinetic energy)1.
Say it: “Where is the energy hiding now?”Simple physics experiments with marbles: a homemade Newton's cradle
A Newton's cradle is the desk toy with hanging steel balls: lift one, let it hit, and one flies out the other side. You can build the same effect flat with marbles, the setup used in STEPS to STEM, a curriculum by Aaron Isabelle and Gilbert Zinn1.
The marble line (a flat Newton's cradle)
- 2 yardsticks or rulers laid side by side, a marble-width apart
- 6 to 8 marbles of the same size
- Pencil and the chart below
- Adult supervision: marbles are a choking hazard for young children. Count them out and back in.
- Put 4 marbles touching each other in the middle of the track1.
- Gently roll 1 marble into the line. Ask: how many rolled away at the far end?
- Predict, then roll 2 together. Then 3. Record each result1.
- Roll 1 harder. Does the last marble go farther?1
- Challenge: roll 1 from the left and 2 from the right at once1.
| Marbles rolled in | Your prediction | Rolled out | Matched? |
|---|---|---|---|
| 1 | ____ | ____ | ____ |
| 2 | ____ | ____ | ____ |
| 3 | ____ | ____ | ____ |
| 1 left + 2 right | ____ | ____ | ____ |
Why does it work? The rolling marble carries energy of motion, which passes from marble to marble until the last one rolls away. The book adds a second rule that explains the exact count1:
The total momentum must stay the same.1
Pendulum experiments: what changes the swing?
A weight on a string is a simple pendulum, pulled by gravity1. Most kids guess a heavier weight swings faster. Physics says no: a simple pendulum's timing depends only on its length and gravity, not its mass5. A perfect prediction test.
Long string, short string, heavy weight
- String and tape
- A table edge
- 3 metal washers
- A phone timer
- Tape a ruler-long string to the table edge with 1 washer on the end.
- Pull it back a little and let go. Count full swings in 30 seconds.
- Predict, then test: 3 washers on the same string.
- Predict, then test: a string twice as long with 1 washer.
- Ask: which change mattered, weight or length?
-
01Stretch a line.
Tie a string tight between two chair backs1.
-
02Hang two weights.
Two equal weights on short strings, 20-30 cm apart1.
-
03Start one.
Swing weight A. It slows and stops while B starts swinging, then they switch1.
-
04Explain it.
Each swing of A nudges the shared line, handing energy to B: a coupled pendulum1.
Friction ramp: physical experiments at home
Friction is why a toy car stops on carpet but keeps going on the kitchen floor2. Keep the ramp the same, change only the surface, and you have a fair test. Ramp steepness is its own experiment, covered in our ramps guide.
-
01Build one ramp.
A board or cardboard sheet on 2 books. Mark a start line with tape.
-
02Pick three surfaces.
Bare floor, a towel, a sheet of foil or paper laid at the bottom.
-
03Predict.
Which surface lets the car roll farthest? Which stops it fastest?
-
04Release, don't push.
Let go at the line 3 times per surface and measure with a tape measure or count floor tiles.
- "It stopped because it's tired."
- "Something got in its way. What was it?"3
Energy science you can watch: comeback can and marble coaster
STEPS to STEM has an energy puzzle: a can with a rubber band and a small weight inside. Roll it away and it stops, then rolls back1. The rolling winds up the rubber band, storing energy; the band unwinds and rolls the can home. It never quite reaches the start, because friction turns some energy into heat1.
Marble roller coaster STEM project
A marble run tells the same story with gravity. Objects store energy depending on their position1, so a marble at the top has energy that becomes motion on the way down.
- Cut paper towel tubes in half lengthwise to make open channels (adult does the cutting)
- Tape them down the side of a big cardboard box in a zigzag
- Start high: the first drop powers the whole ride
- Add one hill. Can the marble climb one as tall as the start?
- Finish in a cup
If the marble can't climb the hill, it is out of energy.
Catapult science fair project: a STEM catapult challenge
A catapult combines two ideas. The arm is a lever, one of the simple machines on DK's machines page2, and the rubber band stores energy like the comeback can1. Kids learn simple machines by experimenting, not by memorizing names3.
Craft stick catapult challenge
- 7 craft sticks
- 4 or 5 rubber bands
- A plastic spoon
- Pom-poms
- Tape measure
- Adult supervision for rubber bands and small parts.
- Band 5 stacked sticks at both ends: the pivot block.
- Band 2 sticks at one end only and slide the pivot block between them.
- Tape the spoon to the top stick, press down, let go.
- Fair test: move the pivot, measure distance 3 times each.
Physics science fair projects: questions that work
A good project changes one thing, measures one thing and keeps everything else the same. Each experiment above becomes a project with the right question.
| Question | Change | Measure | Best for |
|---|---|---|---|
| Does a heavier weight swing faster? | Washers on the string | Swings in 30 seconds | Ages 6-10 |
| Which surface stops a car fastest? | Floor surface | Distance rolled | Ages 5-10 |
| How many marbles leave the line? | Marbles rolled in | Marbles rolled out | Ages 5-8 |
| How high can a coaster hill be? | Hill height | Did it make it? (yes/no) | Ages 7-10 |
| Where should the catapult pivot go? | Pivot position | Launch distance | Ages 7-10 |
Heavy things swing faster on a pendulum.
A simple pendulum's timing depends on its length and gravity, not its mass5.
Moving things stop on their own.
They keep moving unless an unbalanced force acts on them4. Friction is usually that force.
What to expect by age
Can: Predict and describe with push, pull, gravity and friction23.
Try: Marble line and friction ramp, with tallies.
Can: Run 3 tries per setup and explain results with energy words1.
Try: Pendulum or catapult as a fair project with a bar graph.
Frequently asked questions
What are easy physics experiments for kids at home?
Roll marbles into a line of marbles, time a washer on a string, or race a toy car onto different surfaces. Each shows one idea: momentum1, pendulum timing5 or friction2.
How do I do a Newton's cradle science fair project?
Use the marble track: 4 marbles in a ruler track, then roll 1, 2 and 3 in and record how many roll out1. The question: does the number out always match the number in?
What are good energy science fair projects for kids?
The comeback can and the marble roller coaster both show energy changing form. The can turns rolling energy into stored rubber band energy and back, and friction makes it stop short1.
What are physics ideas for science fair at elementary level?
Pick one change and one measurement: pendulum length versus swing count5, or pivot position versus catapult distance. Repeat each test 3 times.
What are gravity science fair projects for young kids?
A pendulum and a marble run are both gravity projects: gravity pulls the swinging weight1 and the falling marble. For ages 5-7, rolling a toy car down ramps of different shapes and asking which one they would drive on is a good start3.
Keep exploring
- Ramps, cars and your child's first fair test The full ramp steepness experiment.
- Center of gravity for kids Gravity and balance, with a cereal box.
- Science fair board and the scientific method Present any project above.
If you want a kit for this
Everything above works with household things. If your child wants to keep building ramps, tracks and launchers, our cardboard kit is made for that kind of tinkering.
Build it with / Ages 5-7STEM Cardboard Construction KitKid-safe tools turn any box into a machine.$42.99GoP Toys sells the kit mentioned above. None of the sources cited tested our products.