A box of books sits on a shelf. The Earth pulls the box straight down, all the time. So why doesn't the box crash through the shelf? Something must hold it up.
The holder is the shelf itself, and holding up is a push.
The shelf pushes up on the box. That push is what stops the Earth's pull from dragging the box through.
A shelf pushing sounds strange, so make the push visible: stand on a trampoline. The surface dips under your feet and pushes back up on them. A shelf does the same as the trampoline. It dents under the box far too little to see, and it pushes back.
The push is not only upward from floors and shelves. Press your hand against a wall, and the wall pushes back on your hand.
The pattern: a surface pushes on whatever rests on it or presses against it. That push from a surface is called the normal force.
A cereal box sits on a pantry shelf. Which force is the normal force on the box?
The word 'normal' here is an old math word for square-on to a surface; it does not mean 'usual'. The direction story comes next lesson.
A souvenir magnet clings to a refrigerator door, pressing against it. Does a normal force act on the magnet?
One boundary: the normal force needs contact with a surface. Weight needs no contact at all. A force from a touching surface is the normal force; the Earth's pull from a distance is weight.
Tobias leans his back against a hallway wall while he waits. Which force is the normal force from the wall?
A laptop rests on a desk. Name the normal force on the laptop in full.
A surface pushes on whatever rests on it.
Here the surface is the desktop, and the laptop rests on it.
The desk pushes up on the laptop: that push is the normal force on the laptop.
Lena presses a poster flat against a wall while the tape sets. Which normal force acts on the poster, and from which object?
A surface pushes on whatever presses against it, sideways surfaces included.
The poster presses against the wall, so the wall pushes back on the poster.
The wall exerts a normal force on the poster, pushing the poster away from the wall.
A flowerpot rests on a windowsill. Which statement names the normal force on the pot?
In which scene does a normal force act on the ball?
Mira stands on a diving board, and the board bends under her. What does the bent board do?