In physics, a force is simply a push or a pull on an object. Forces are all around us, shaping every interaction. When you kick a ball, you're applying a force. When a magnet snaps to your fridge, that's a force at work. Even just standing still, the force of gravity is pulling you toward the center of the Earth.

Because forces have both a strength (magnitude) and a direction, they are what we call vector quantities. It matters not just how hard you push something, but also which way you push it. Pushing a box forward will move it across the room, but pushing down on it won't move it at all.

There are many kinds of forces in the universe, but most of our daily experiences can be explained by just a few common ones. Let's look at the main players you'll encounter.

Next up is gravity, the invisible force that pulls objects toward one another. The Earth's gravity is what keeps your feet on the ground and causes an apple to fall from a tree. The more massive an object is, the stronger its gravitational pull.

Whenever two surfaces are in contact, there's usually friction. This is a force that opposes motion. If you slide a book across a table, friction is the force that slows it down and eventually stops it. Rough surfaces, like carpet, create more friction than smooth surfaces, like ice.

Finally, there's the normal force. This is the support force exerted by a surface on an object resting on it. If you place a book on a table, gravity pulls it down. So why doesn't it fall through the table? Because the table pushes back up with an equal and opposite force. That upward push is the normal force. It's always perpendicular to the surface.

How do we measure how strong a push or pull is? In physics, the standard unit of force is the newton, named after Sir Isaac Newton. It's abbreviated with a capital N.

One newton isn't a very large force. For example, the force of gravity pulling on a small apple is about 1 N. The weight of a typical adult is often several hundred newtons.

To measure force in a lab, scientists often use a spring scale. It's a simple device with a spring inside that stretches when a force is applied. The more the spring stretches, the greater the force. The scale is marked in newtons, allowing for a direct reading of the force's magnitude.

Now that we've covered the basics of what forces are, we can explore how they interact with each other.