6.3 · Gravity Is Always Pulling

From Ohio 5th Grade Science Power Workbook · Chapter 6 · Lesson 6.3.

Big idea: Gravity is a pull that acts on everything all the time, not only on things that are falling.

Learning goals: Describe gravity as a force

Explain that gravity acts on resting objects too

Explain why a resting object does not fall through the floor

A pull that never switches off

Gravity is a pull. On Earth it pulls everything toward the ground.

It does not wait until something starts falling. It is pulling on you right now, and on the chair you are sitting on.

Why a book on a desk stays put

Gravity pulls the book down. The desk pushes the book up with an equal force.

Those two forces are balanced, so the book does not move. Gravity did not stop acting — it was canceled out.

Worked examples

Question: A student says gravity is not acting on a book that is sitting still on a table, because the book is not falling. Explain what is really happening.

Steps: Ask whether gravity ever switches off. It does not; it pulls on everything all the time.

Ask what else is touching the book. The table is pushing up on it.

The downward pull and the upward push are equal and opposite, so they are balanced and nothing moves.

Answer: Gravity is still pulling the book down. The table pushes up with an equal force, so the forces are balanced and the book stays still.

Common mistakes

Gravity does not wait for something to fall

We notice gravity when something drops, so it is easy to think that is the only time it works.

Gravity is pulling on every object all the time. A book resting on a table is not falling because the table pushes up on it just as hard. A ball tossed upward is not falling yet either, but gravity is already pulling on it and slowing it down.

Check your thinking: Ask what is holding the object up. If something is, gravity is still pulling — it is simply being balanced.

Ohio connection

Why a bridge over the Cuyahoga has to push up

Every bridge across an Ohio river carries traffic that gravity is pulling straight down, all day, every day.

The bridge does not stop gravity. It pushes up with an equal force, so the forces balance and the cars stay on the road instead of moving downward.

Think: If a bridge could not push up hard enough, what would happen to the balance of forces?

Remember

Resting on something means it is being held up

An object resting on something is not falling because that thing pushes up on it. A table, the ground, a shelf. Gravity is the down force; the support is the up force.

Practice tip

Remember: Gravity is always the down force.

Tip: In any Ohio question about a resting object, gravity is pulling down and something is pushing up. Naming both is usually what earns the second point.

Written practice

Explain why a person standing on the floor does not sink through it, even though gravity is pulling them down.

Sample response: Gravity pulls the person downward all the time. The floor pushes up on them with a force of the same size, so the two forces are balanced and cancel out. Because the forces are balanced, the person's motion does not change and they stay where they are.

Scoring guide: 1 point: says the floor pushes up on the person with a force equal to gravity's pull.

1 point: explains that the two forces are balanced, so the person's motion does not change and they do not sink.

This targets the listed misconception that gravity only acts on falling objects.