1. A push or a pull on an object is called a force.
Forces
A push or a pull on an object is called a force.

2. Contact Forces
A contact force is a push or a pull on one object by another that is touching it.
Contact forces can be weak or strong.

3. The Force of Friction
Friction force is the force exerted by a surface as an object moves across it or makes an effort to move across it.
Friction depends upon the nature of the two surfaces and upon the degree to which they are pressed together.
The friction force often opposes the motion of an object.

4. The Force of Tension
The tension force is the force that is transmitted through a string, rope, cable or wire when it is pulled tight by forces acting on opposite ends.
The tension force pulls equally on the objects on the opposite ends of the wire.

5. Normal Force
The normal force is the support force exerted upon an object that is in contact with another stable object. If a book is resting upon a surface, then the surface is exerting an upward force upon the book to support the weight of the book.

6. Air Resistance Force
The air resistance is a special type of frictional force that acts on objects as they travel through the air. This force is most noticeable for objects traveling at high speeds and those with large surface areas.

7. Applied Force
An Applied Force is a force that is applied to an object by a person or another object.

8. Spring Force
Spring force is the force exerted by a compressed or stretched spring upon an attached object.
The magnitude of the force is directly proportional to the amount of stretch or compression of the spring.

9. Non-Contact Forces
A non-contact force is a force that one object can apply to another object without touching it.
These forces also have direction and strength.

10. Gravitational Force
Objects fall to the ground because Earth exerts an attractive force on them. This force is equal to the weight of the object.
Gravity is an attractive force that exists between all objects that have mass. The greater the mass, the greater the attraction.
The closer the objects are, the greater the attraction.

11. Magnetic Force
This is the force that exists between two magnets, caused by the interaction of their magnetic fields.
This force causes the magnets to attract or repel one another.

12. Electrical Force
This is the force created between two charged objects or particles. The objects either attract or repel each other.
As distance increases, the electric force decreases.