Force 

In our everyday lives, Force is an effort that is needed to put a stationary object into motion or bring a moving object to rest. In physics, force is a vector quantity, meaning it has both direction and magnitude, which causes a change in the state of motion or shape of an object.

1.0Force: Push and Pull

Force can also be understood by the push (the force that moves an object away from the source of force) and pull (the force that moves an object close to the source of force) applied to an object, which causes the object to change its state of motion or rest. The interaction of forces of different types (Contact force, Non-Contact Force) causes an object to accelerate, deform, or stop. Force can be denoted with the letter F, and the SI unit of the force is the Newton(N). 

2.0Types of Force 

1. Contact Forces: Forces that need physical contact with the object to leave an impact are classified as Contact Forces. The Contact forces are further divided into different types of forces, such as: 

• Frictional Force: Frictional force is an opposite force that resists the tendency of motion or relative motion. For example, walking (an opposite force is applied by the surface), pushing an object, or car tyres on the road. 
• Tension Force: Tension force is a force applied by a string, rope, cable, or any other flexible material when it is stretched. This force acts along the object's length and resists the tension that pulls it apart or is stretched out.
• Normal Force: The Normal force is the perpendicular force acting on an object at rest to support and balance the weight of that object. It always acts perpendicular (Normal) to the surface. 

2. Non-Contact Forces: Non-contact forces are the forces that require no physical contact between force and the object. These are the forces that are responsible for many natural phenomena like the rotation and revolution of heavenly objects (Gravitational force). Non-Contact forces are classified into: 

• Gravitational Forces: It is the force that exists between two objects with mass which attract each other at the centre of the objects from a distance. In physics, the gravitational force(Fg) is directly proportional to the product of the mass(m1 & m2) of both objects and inversely proportional to the square of the distance(r) between them. Mathematically, gravitational force can be expressed as:

$F_g=G\frac{m_1{m}_2}{r^2}$

Here, G is the Gravitational Constant with the value $6.67\times 10^{-11}N{m}^2/k{g}^2$

• Magnetic Force: It is the force exerted by the magnetic field of any moving charge or a magnet on an object within the area of its influence. It can either attract or repel the object based on the nature of the object within the field. 

3.0Force And Motion

As we know, force causes an object to change its state of motion, which further causes it to either accelerate the object or halt it. The direction and the magnitude of the force will decide whether an object will accelerate or decelerate. Observing this relation between force and motion of an object, Newton, the greatest scientist of the century, gave three laws of motion that explain this relation clearly: 

1. First Law or the Law of Inertia: It states that if an object is at rest or in motion, it will continue to remain at rest or in motion unless external forces change its state of motion. The body here resists the change in its state of motion which is known as the inertia of the body. Hence, this law is also known as the Law of Inertia. 
2. Second Law of Motion: This law gives the mathematical expression of the force, according to which force F is directly proportional to the product of the mass (m) of the object and acceleration (a). 

F=ma

3. Third Law (Action & Reaction): This law very famously states that every action has an equal and opposite reaction. This law gives the classic example of the interaction of forces, which also states that forces always come in pairs; for example, the Earth attracts the moon, but the moon also attracts the Earth with equal force.

4.0Solved Questions On Force

Problem 1: A car of mass 1000 kg is accelerating at a rate of 3 m/s. Calculate the force exerted by the engine to accelerate the car.

Solution: Mass of the car, m = 1000kg

Acceleration, a = 3m/s² 

$F=ma$

$F=1000\times 3=3000N$

Problem 2: Two objects, with masses of 10 kg and 20 kg, are placed 2 meters apart. What is the gravitational force between them?

Solution: Let the mass of object 1, m₁ = 10kg 

Let the mass of object 2, m₂ = 20kg

Distance between the objects, r = 2m 

$F_g=G\frac{m_1{m}_2}{r^2}$

$F_g=6.67\times 10^{-11}\times \frac{10\times 20}{2^2}$

$F_g=3.337\times 10^{-8}N$

Problem 3: Why does a bus take longer to stop compared to a small car?

Solution: The bus has a much greater mass than a small car. According to Newton's second law, the force required to stop an object depends on its mass and acceleration (or deceleration in this case). A greater mass requires a greater force to bring it to rest.