In statics, we look at objects that aren't moving. To understand how these objects stay still, we need to see the different types of forces acting on them. Knowing about these forces is really important for building things like bridges and buildings.

Let’s start with external forces. These are the pushes and pulls coming from outside the object. Here are some examples:

• Gravity: This is the force that pulls everything down toward the ground. It represents the weight of the object.
• Applied Forces: This is when someone or something pushes or pulls on the object. For example, if a worker tries to lift a heavy beam, that's an applied force.
• Reaction Forces: These are the forces from supports or connections that react to the outside forces. For instance, when a cable holds something up, it’s pulling on the cable. Or when something sits on the ground, the ground pushes back up with a normal force.

Now, let’s talk about internal forces. These forces happen inside the object itself and help keep it strong. Here are the main types:

• Tensile Forces: These forces try to pull or stretch the material. For example, if a cable is holding up a weight, the forces inside the cable are tensile.
• Compressive Forces: These forces push or squeeze the material. For example, the columns of a building are pushed down by the weight they are holding up.
• Shear Forces: These forces make parts of a material slide past each other. This often happens in beams when they are pushed side to side.

For an object to stay still, both external and internal forces have to balance each other out. This means that if you add up all the forces acting on the object and the turning effects (called moments), they should equal zero. We can say this with a simple rule:

All Forces = 0
All Moments = 0

When engineers understand these basic forces, they can design structures that are strong and safe. This helps buildings and bridges hold up under different weights without breaking.