Force is defined as the push or pull movement that changes the motion of the body. It is an external agent that is applied on the body. Force is divided into two main types, contact forces and Non- contact forces. Force is a vector quantity and hence has both magnitude and direction. Forces can also long-range force or short-range force. Long range is gravitational force or electrostatic force while short range force is the atomic or nuclear force. The long-range force decreases with increase in distance rapidly as they have an inverse relation. 

Force can perform the following actions of the body -:

• Pull the object
• Push the object 
• Change or alter the shape of the object
• Change the direction of motion of the object, alter speed of the object.
• Stop a moving body or object. 

Units of force 

SI unit of force is Newton, Cgs unit is Dyne while the British unit is Slug.

Measurement of force

• Applying acceleration to a body.
• For measuring force at times, the change that it has caused can be considered like in the case of the body that has changed its shape .So the degree of change can be the measurement of force.

Contact forces

Contact forces are the one as the name suggests there is a contact between the two bodies under consideration. That means one body is exerting force on the other body because of the contact between the two.

So, the force that is found due to or by the means of physical contact between two bodies is known as contact force.

Some of the examples of content forces in day to day life are – Pushing a door, Playing Basketball, Hitting the football, working on laptop, pushing sofa and so on.

Types of contact forces

Contact forces are subdivided into some types these are as follows -:

• Spring force -The Hooke’s law talks about spring force. The spring force is a result of movement or displacement of molecules. The displacement of molecules is in a direction opposite to the displacement of spring. It is a type of Normal force.
• Applied force – Muscular force is the other name for applied force. The force due to action of muscles.
• Air resistance force -It is a type of Normal force. Air resistance force is the one in which the force acts in the opposite direction in presence of gas. Air resistance force is directly proportional to the area under contact, if the area increases the air resistance force increases and also if the velocity through the gas increases.
• Frictional force- Friction is a dissipative force that acts opposite to the direction of motion and offers resistance to the motion of the object. It is a result of contact with the surface or when there is an interaction between the object and the surface and the object tries to Move this force offered by resistance. It is a type of Normal force.
• Normal force – It is a force that is result of contact between surfaces. As this force acts perpendicular to the surface under consideration this is known as Normal force. Some examples of Normal force are – spring force, air resistance force, tension force and so on.
• Tension force – The force that is produced with the Help of rope, cable or string.  This force only pulls the suspended mass attached to it. It doesn’t have the pushing ability.

Non-contact forces

Non-contact forces are those that don’t have contact between the two bodies. This force doesn’t arise due to physical contact between the surfaces but acts through the space between the two bodies.

Some of the examples of Non-contact forces are as follows -:

• Gravitational force
• Nuclear force – Strong
• Weak Nuclear force
• Electromagnetic force

1. Gravitational force- The force that is present due to the attraction between the two objects is defined as the gravitational force.
2. Electromagnetic force- it is due to the electric or magnetic affinity of the molecules that generates this force and results in binding of atoms and solids 
3. Nuclear force – it can divide based on strength as – Weak and strong.Weak nuclear force-The force is present between radioactive decay molecules and is generated during their decay.While, Strong nuclear force is required in Binding of the nucleus.

Conclusion 

Force by definition is the simple pull and push movement of the object. It is an agent that can perform various effects and changes on the object under consideration like altering shape or size and affecting its movement by decreasing speed, stopping the moving object or changing the direction. Further force can be measured with the help of the acceleration or the degree of change that it has brought. The SI unit of Force is Newton and based on the contact between the two bodies or surfaces they are classified into two categories these are – Contact force and Non-contact force. Contact forces are Have a physical contact between the surfaces. There examples being – Tension force, Frictional force etc. While non -contact force doesn’t have contact with the body but acts through the space in between. Examples – Nuclear force and gravitational force.