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Science Launch G3 / Week 01 / Wednesday
3/6
Week 01 · Balanced or Not?

Wednesday

The two-string test
// Pushes, pulls and what they do
⏱ about 15 min

Wednesday: The Two-String Test

Rocket ties two strings to a shoebox. "Let's see what happens!" he cheers. He yanks one string, and the box zooms off the table.

Raven catches it. "What do you notice when only one side pulls?"

Nova shines a soft light on the second string. "Try using both strings," she says. "Change one thing at a time."

Rocket nods. This time he will plan first.

Your investigation

You will test balanced and unbalanced pulls on a box. You need a partner for this one.

  • An empty shoebox or small cardboard box
  • Two pieces of string, each about as long as your arm
  • Tape
  • A smooth table or floor
  • A partner
Safety first
Pull gently. Never yank the string toward a face.
Keep the box low and on the table or floor.
A grown-up cuts the string if scissors are needed.
  1. Tape one string to each end of the box.
  2. Set the box in the middle of the table.
  3. You hold one string. Your partner holds the other.
  4. Both pull gently with the same strength. Watch the box.
  5. Now your partner pulls a little harder. Watch the box again.
  6. Switch, so you pull harder. Watch which way the box goes.
MAKE A PREDICTION
  • Read the question.
  • Tap your answer.
You and your partner pull equally hard. What will the box do?
Your partner pulls harder than you. Which way will the box go?
TestMy pullPartner pullWhat the box did
1gentlegentle
2gentleharder
3hardergentle
In which test number were the pulls balanced?
WHY THIS EXERCISEIn test 1 the pulls were equal and opposite, so they were balanced.

Check your results

Scientists look back at their data to see what it means.

In a fair test, you change only one thing at a time. Here you changed only how hard each person pulled.

ResultTrue or false?
When both pulls were gentle, the box stayed still.?
The box moved toward the weaker pull.?
A bigger pull on one side made the forces unbalanced.?
WHY THIS EXERCISEEqual pulls balanced. The box moved toward the stronger pull.
WHAT WOULD HAPPEN IF...
  • Read the question.
  • Tap your answer.
What if you both pulled very hard, but equally hard?
What if your partner let go of the string while you pulled?

Nice investigating! You saw balanced and unbalanced forces with your own eyes. Tomorrow we learn more about unbalanced forces.

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