• Non-contact forces are forces that act on an object without any physical contact. They are caused by the interaction between the objects due to their proximity to each other. Some examples of non-contact forces include:

  • Gravity: Gravity is the force that attracts objects towards the center of the Earth. It is a fundamental force of nature that acts on all objects with mass, regardless of their composition.

  • Magnetic force: Magnetic force is the force exerted by a magnet on a magnetic object. It arises from the alignment of the atoms and molecules of the magnetic object with the magnetic field of the magnet.

  • Electric force: Electric force is the force exerted by an electric field on a charged particle. It arises from the interaction between the electric charges of the charged particle and the electric field.

  • Electrostatic force: Electrostatic force is the force exerted between electrically charged objects. It arises from the interaction between the electric charges of the objects.

  • Nuclear force: Nuclear force is the force that holds the protons and neutrons of an atom together. It arises from the interaction between the subatomic particles of the atoms.

• All these forces are examples of non-contact forces, they act on objects even when they are not in contact with each other and their action depends on the properties and characteristics of the objects involved. Understanding the different types of non-contact forces and how they interact with objects is crucial in many fields, such as physics and many other branches of science.

• It is common to ignore forces like air resistance and gravity in statics calculations because they are typically much smaller than the other forces acting on an object.

  • In statics, the main focus is on the forces that are acting on an object in order to determine whether the object is in equilibrium or not. The forces that are typically considered in statics calculations include tension, compression, shear, and friction.

• Air resistance is a fluid force that acts on an object when it moves through the air.

  • It is generally much smaller than the other forces acting on an object, and it becomes less significant as the speed of the object becomes smaller.

  • Therefore, it is often ignored in statics calculations because it has a minimal effect on the overall equilibrium of the object.

• Gravity is a non-contact force that acts on all objects, pulling them towards the center of the Earth.

  • It can be considered as a constant force that acts in a downward direction and its effect is usually taken into account in the weight of the object.

  • However, in a statics problem when the object is not moving, the effect of gravity is already accounted for by the normal force acting on the object and it is not necessary to include it in the calculations as long as the object is not moving.

• In summary, it is common to ignore forces like air resistance and gravity in statics calculations because they are typically much smaller than the other forces acting on an object and their effects are usually negligible.

  • The main focus of statics is to determine whether an object is in equilibrium or not, and these forces are not critical to that calculation. 

When Not to Ignore

• It is generally safe to ignore commonly-negligible forces like air resistance and gravity in statics calculations because they are typically much smaller than the other forces acting on an object.

  • However, in certain situations, it may be critical not to ignore these forces.

    • High-speed motion: When an object is moving at high speeds, the air resistance force can become significant and can no longer be ignored. For example, when designing a high-speed vehicle, the aerodynamic forces acting on it must be taken into account.

    • Lightweight objects: When an object is lightweight, the gravitational force acting on it can become significant in relation to the other forces acting on it. For example, when designing a lightweight structure such as a bridge, the weight of the structure must be taken into account.

    • Fluid-structure interaction: When an object is submerged in a fluid, the fluid forces acting on it can become significant. For example, when designing a boat or a submarine, the hydrodynamic forces acting on it must be taken into account.

    • High-altitude engineering: When an object is located at high altitudes, the gravitational force acting on it can become significant in relation to the other forces acting on it. For example, when designing a structure such as a building or a tower that is located at high altitudes, the weight of the structure must be taken into account.

• In these and other situations, it may be critical not to ignore commonly-negligible forces like air resistance and gravity in statics calculations, as they can have a significant effect on the overall equilibrium of the object, and thus on the safety and stability of the structure.