Hour of Science

Physics

Simple physics demos with string, paper and tape

Physics is the science of pushes, pulls, energy and light. These demos turn big ideas like forces and friction into something kids can see, time and measure.

The big ideas

Each demo shows one idea. Balloon rockets show that a push in one direction gives a push in the other. Ramps show stored energy turning into motion. Pendulums show a surprising rule about timing, and static balloons show an invisible force at work. Kids don't need the vocabulary first. Let them see it happen, then give the idea a name.

The demos

Balloon rocket

Ages 5 and up, 20 min, adult helps

You need

  • A long piece of string
  • A drinking straw
  • A balloon
  • Tape
  • Two chairs

Steps

  1. Thread the string through the straw.
  2. Tie the string tight between two chairs.
  3. An adult blows up the balloon and pinches the end shut.
  4. Tape the balloon to the straw, then let go.

What's happening: Air rushes out of the back and the balloon is pushed forward. Every push comes with an equal push the other way, which is Newton's third law.

Safety: An adult inflates the balloon. Balloons are a choking hazard for children under 8.

Go further: Does a fuller balloon go farther? Mark each finish with tape and measure.

Pendulum test

Ages 7 and up, 20 min, adult nearby

You need

  • String
  • A few metal washers
  • Tape and a table edge
  • A timer
  • A ruler

Steps

  1. Tape the string to the table edge so it hangs free.
  2. Tie on one washer.
  3. Pull it to the side, let go, and count swings in 20 seconds.
  4. Change one thing, either the length or the number of washers, and count again.

What's happening: A pendulum's timing depends mostly on its length. Shorter strings swing faster, while extra weight hardly changes anything.

Safety: Keep washers away from toddlers.

Go further: Test five string lengths and draw a graph of swings against length.

Ramp race

Ages 4 and up, 20 min, adult nearby

You need

  • A stiff board or big hardback book
  • A stack of books
  • A toy car or ball
  • A tape measure

Steps

  1. Rest the board on one book to make a low ramp.
  2. Let the car go from the top without pushing.
  3. Measure how far it rolls past the end.
  4. Add a book and repeat.

What's happening: A higher start gives the car more stored energy. As it rolls down, that energy turns into motion, so it travels farther.

Safety: Keep ramps low and steady, and roll toward open floor, away from stairs.

Go further: Run the same ramp onto carpet and onto a smooth floor to see what friction does.

Static balloon

Ages 4 and up, 10 min, adult helps

You need

  • A balloon an adult has blown up and tied
  • Small bits of torn tissue paper
  • A tap

Steps

  1. Rub the balloon on clean, dry hair or a wool sweater for ten seconds.
  2. Hold it just above the paper bits.
  3. Then hold it near a thin stream of tap water without touching.

What's happening: Rubbing moves tiny charged particles called electrons onto the balloon. The charged balloon pulls on the paper and even bends the water.

Safety: An adult inflates the balloon. Dry days work best.

Go further: Rub for 5, 10 and 20 seconds and count how many paper bits each time lifts.

Paper helicopter

Ages 5 and up, 15 min, adult helps

You need

  • Paper
  • Child-safe scissors
  • A paper clip

Steps

  1. Cut a strip of paper about the size of a hand.
  2. An adult helps cut a slit halfway down from the top.
  3. Fold the two flaps opposite ways to make blades, and clip the bottom.
  4. Drop it from shoulder height.

What's happening: Air pushes up on the angled blades as it falls, which makes it spin. Spinning slows the fall.

Safety: Drop from standing height. No climbing on furniture or leaning out of windows.

Go further: Time drops with short and long blades. Which falls slowest?

Sink or float

Ages 3 and up, 15 min, adult nearby

You need

  • A tub of water and a towel
  • An apple, a metal spoon, a cork, a plastic lid, a dry sponge
  • A lump of modeling clay

Steps

  1. Before each test, guess: sink or float?
  2. Place the object gently on the water.
  3. Sort everything into two piles.
  4. Talk about what the floaters have in common.

What's happening: Floating depends on density compared with water, more than on weight. A big apple floats because it holds air, while a small spoon sinks.

Safety: Stay with young children near water, even a shallow tub.

Go further: Roll the clay into a ball that sinks, then shape the same clay into a boat that floats.

Water drop lens

Ages 5 and up, 10 min, adult nearby

You need

  • Clear plastic wrap
  • A straw or dropper
  • Water
  • A printed page

Steps

  1. Lay the plastic wrap flat over the page.
  2. Place one drop of water on the wrap.
  3. Compare the letters under the drop with the ones around it.

What's happening: The curved drop bends light like a magnifying glass, so the letters underneath look bigger.

Safety: Keep plastic wrap away from babies and toddlers.

Go further: Try a small drop and a big drop. Which magnifies more?

Making it measurable

Older children get more from physics when they measure. A tape measure, a phone timer and a notebook are enough. Run each test three times and take the middle result, because one strange throw or wobble can throw off a single try. Then turn the numbers into a simple bar chart. The scientific method page uses the pendulum as a full worked example.