Monday
Monday: Pushes and Pulls
Rocket and Raven each grab one end of a soft jump rope at the Field. The knot in the middle hangs over a tape line.
"Pull!" Rocket says. They both lean back. The rope goes tight. The knot does not move.
"What do you notice?" Raven asks through her teeth. "We are both pulling hard, and nothing is happening."
Nova hovers above the knot. "Is nothing happening? Or are two things happening at once?"
Rocket eases off for a second. The knot slides toward Raven. He pulls again and it stops.
"Two pulls," Rocket says. "When they match, the knot stays. When they do not, it moves."
Raven lets go and grins. "Welcome to forces."
A force is a push or a pull
A physics text from OpenStax says it simply: a force pushes or pulls an object.
The push or pull may come from a person, from another object, or from the gravitational pull of Earth.
Forces have different strengths and directions. Some forces are stronger than others, and they can act in different directions.
When several forces act on one object, they combine. Adding together all of the forces gives the total force, or net force.
The rope knot had two forces on it: Rocket's pull one way and Raven's pull the other way.
| Force at the Field | Push or pull? | What it acts on |
|---|---|---|
| A hand rolling a ball | push | the ball |
| A rope pulled tight | pull | the knot |
| Earth's gravity | pull | everything near Earth |
| A foot stopping a rolling ball | push | the ball |
- Read the question.
- Tap your answer.
Forces have strength and direction
A gentle push and a hard push are both pushes, but they have different strengths.
A push to the left and a push to the right have the same strength but opposite directions.
When two equal pulls point in opposite directions, they cancel. The net force is zero. The knot stays put.
When one pull is stronger, they do not cancel. The net force points toward the stronger pull, and the knot moves that way.
| Statement | True or false? |
|---|---|
| A force is a push or a pull. | ? |
| Earth's gravity is a kind of pull. | ? |
| All forces have the same strength. | ? |
| The net force is all the forces added together. | ? |
Have one partner pull a little harder. Watch which way the middle moves.
Write both results in your Field Log with the words push, pull and net force.
Tug of war stays gentle: no sudden letting go, soft grass or carpet underfoot, and nobody wraps the rope around a hand.
The force facts come from an OpenStax physics text and NASA Glenn Research Center, which you can read at nasa.gov.
Great first look at forces. Tomorrow you will learn the rule that tells what balanced forces do to motion.