Oracle IAS, the best coaching institute for UPSC/IAS/PCS preparation in Dehradun brings to you UKPCS Science (paper #6).

What is Force?

In physics, a force is any interaction that, when unopposed, will change the motion of an object. A force can cause an object with mass to change its velocity (which includes to begin moving from a state of rest), i.e., to accelerate. Force can also be described intuitively as a push or a pull. A force has both magnitude and direction, making it a vector quantity. It is measured in the SI unit of Newton and represented by the symbol F

For an object to move one needs to apply an unbalanced force ie applied force should be greater than the frictional force.


Newton’s first law of motion states that an object at rest remains at rest and an object in motion remains in motion with the same velocity unless acted upon by what we call an unbalanced force.

Newton’s first law of motion is also referred to as the law of inertiaInertia is simply the resistance to change in motion. In short, objects tend to keep doing what they are already doing.

Example:1) a car moving on a road with a constant velocity. If the driver removes is foot from the pedal the velocity starts decreasing. This is due to the friction force (unbalanced force=friction)

2) Have you ever experienced a dizzy feeling after coming to a stop in a descending elevator? Better hold on to the railing! Our body and all its contents move down along with the elevator. Once the elevator comes to a sudden stop, the floor of the elevator applies an external force to our body, causing it to come to a stop as well.

Newton’s second law of motion provides the explanation for the behavior of objects when forces are applied. The law states that external forces cause objects to accelerate, and the amount of acceleration is directly proportional to the net force acting on the objects and inversely proportional to the mass of the objects.

EXAMPLE: The same thing can be applied to any moving object. Say you have a friend who is several pounds smaller than you, but they walk exerting the same amount of force as you. Your friend will go a good deal faster than you because their acceleration would undoubtedly be higher.

One of the main reasons why people constantly try to reduce the mass of objects is to be able to increase its speed and acceleration

Newton’s third law states that for every action, there is an equal and opposite reaction.


1)Let’s consider a man attempting to lift a really heavy weight. If the man is able to pull up with a force of 100 lbs, then the weights in turn will pull down with a force of 100 lbs.

2) rocket propulsion

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Hemant Bhatt

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