# Forces: Contact and Non-Contact Forces

## Contact Forces

• A Contact Force is a type of force that requires physical interaction or contact between two objects.
• There are several types of contact forces, including friction, tension, air resistance, normal force, and applied force.
• Friction opposes motion. It is the force that resists the movement of one object sliding or rolling over another.
• Tension arises in flexible objects that are being stretched such as ropes or cables.
• Air resistance or drag is a contact force that opposes motion through air.
• The normal force is the supporting force on a surface that supports the weight of an object resting on it.
• An applied force is a force that is applied to an object by a person or another object.

## Non-contact Forces

• A Non-contact Force is a type of force that acts on an object without touching it.
• There are three main types of non-contact forces: gravitational force, electric forces and magnetic forces.
• The gravitational force is the force of attraction between all masses. The weight of an object is the force of gravitational attraction between the object and the Earth.
• Electric forces occur between charged particles. They can be both attractive (between oppositely charged particles) or repulsive (between particles with the same charge).
• Magnetic forces occur between magnets, or between magnets and magnetic materials. Like electric forces, they can be either attractive or repulsive depending on the orientation of the magnets.

## Balanced and Unbalanced Forces

• A force is said to be balanced when the total force acting on an object is zero. This means the object will stay still if it’s already stationary or continue to move at the same speed in the same direction if it’s already in motion.
• Unbalanced forces are forces that cause a change in the object’s motion. If the total force acting on an object isn’t zero, then the forces are unbalanced, and the motion of the object will change.
• It’s important to note that forces are vectors, they have both magnitude and direction. We need to take into account the direction of the forces when determining whether they are balanced or unbalanced.

## Resultant Forces

• The resultant force is the single force that has the same effect on an object as all the individual forces acting on it combined.
• Resultant force can be calculated by adding or subtracting the magnitudes of individual forces depending on their direction.
• If the resultant force acting on a stationary object is zero, the object remains stationary. If the resultant force acting on a moving object is zero, it continues to move at the same speed and in the same direction.
• If the resultant force is not zero, then the object will accelerate in the direction of the resultant force. This acceleration can be a change in speed (getting faster or slower), a change in direction, or both.

## Newton’s First Law

• According to Newton’s First Law, if the forces acting on an object are balanced or if no forces act on it, the object will remain at rest or move in a straight line at constant speed.
• This property of an object, to keep doing what it’s doing unless acted upon by a force, is known as inertia.