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Science Launch G3 / Week 01 / Thursday
4/6
Week 01 · Balanced or Not?

Thursday

Unbalanced forces
// Pushes, pulls and what they do
⏱ about 15 min

Thursday: Unbalanced Forces

Rocket rolls a marble across the kitchen floor. It glides onto the rug and slows to a stop.

"Nobody touched it," Rocket says. "So why did it stop?"

Raven bends low. "What do you notice about the rug?"

Nova scans the fuzzy rug. "Something rubs against the marble here," she says. "Think about what touches it."

Forces that change motion

When forces do not cancel out, they are unbalanced.

Unbalanced forces change motion. An object can start, stop, speed up, slow down or turn.

Two forces act on things all the time. Here they are.

  • Gravity pulls things toward the center of Earth. It makes a dropped cup fall.
  • Friction works against motion when two surfaces touch. The rug rubbed the marble and slowed it.

Without friction, a car could not move. Its rubber tires grip the road.

Sometimes we want less friction. Ice hockey uses smooth ice so the puck slides easily.

PUT THE MARBLE STORY IN ORDER
  • ?The marble stops.
  • ?Rocket pushes the marble.
  • ?The marble starts rolling.
  • ?The marble rolls onto the rug.
  • ?Friction slows the marble.
WHY THIS EXERCISEA push started the marble, and friction from the rug stopped it.
WHICH FORCE IS IT?
  • Read the question.
  • Tap your answer.
An apple drops from a tree to the ground. Which force pulled it down?
A sled slows down on a patch of dry grass. Which force slowed it?
Which force makes a dropped ball fall?
WHY THIS EXERCISEGravity pulls objects toward Earth, so dropped things fall.
Try it
Roll a ball on a hard floor.
Roll it just as hard on a rug or towel.
Which one stops sooner?

Gravity and friction at work

Gravity and friction often act on the same object.

A sled sits at the top of a snowy hill. Gravity pulls it down the slope.

Snow is smooth, so there is little friction. The sled speeds up.

At the bottom, the sled slides onto bumpy dirt. Friction grows, and the sled slows to a stop.

GRAVITY OR FRICTION?
  • Read the question.
  • Tap your answer.
A leaf floats down from a branch to the ground. Which force pulls it down?
Your shoes grip the floor so you do not slip. Which force helps you?
Which surface gives a sliding block the least friction?
StatementTrue or false?
Friction works against motion.?
Gravity pulls things away from Earth.?
A car needs friction to grip the road.?
A rolling ball on a rug stops because of friction.?
WHY THIS EXERCISEGravity pulls down, and friction resists motion when surfaces touch.
A ball rolls far on a ____ floor.
A ball stops fast on a ____ rug.
Which force slows a sled on bumpy dirt?
WHY THIS EXERCISEFriction works against motion, so the sled slows down.
Safety first
Roll the ball gently and only on the floor.
Clear a path so nobody trips.

Super thinking! Tomorrow we hunt for balanced and unbalanced forces in the world around us.

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