Force is defined as that pull or push which produces or tends to produce, destroys or tends to destroy motion in a body, increases or decreases the speed of the body or changes its direction of motion. Therefore, “Force” is an external or internal agent present to “influence” the natural state of motion of an object. Thus, this is an influence (force) needed to change the natural state of body, that is of rest or of uniform motion.
Depending upon the interaction between a force and an object, forces are classified as, contact and non – contact forces.
What is a Contact Force?
A force which can be applied only when it is in contact with an object is called a contact force. All mechanical forces are contact forces. Contact force is a force that is applied by objects in contact with each other. Contact force acts on a point of direct contact between the two objects. This force can either be continuous as a continuous force or can be momentary in the form of an impulse. Contact force is governed by Newton’s Laws.
Types of Contact Forces: There are six kinds of forces which act on objects when they come into contact with one another.
1. Applied Force: Applied force refers to a force that is applied to an object such as when a person moves a piece of furniture across the room or pushes a button on the remote control.
2. Normal Force: A book resting on a table has the force of gravity pulling it toward the earth, but the book is not moving or accelerating. So, there must be opposing forces acting on the book. This force is caused by the table and it is known as the Normal Force.
3. Tension Force: Tension force is the force applied to a cable or wire that is anchored on opposite ends to opposing walls o other objects. This causes a force that pulls equally in both directions.
4. Frictional Force: Frictional force is the force caused by relative motion of two surfaces that comes into contact with each other.
5. Resting Force: The air resistance is a special type of frictional force that acts upon objects as they travel through the air. The force of air resistance is often observed to oppose the motion of an object. This force will frequently be neglected due to its negligible magnitude.
6. Spring Force: The spring force is the force created by a compressed or stretched spring. Depending upon how the spring is attached, it can pull or push in order to create a force.
F α x, in magnitude, but opposite in direction.
So, F = – kx
k = Spring Constant,
x = Elongation or Compression.