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# How can force affect the motion of an object?

Last updated date: 13th Aug 2024
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Hint: We know that, by definition, any force is an external agent that is capable of changing the state of rest or motion of a body. Think about what would signify a change in the state of rest or motion of the body. Would it be necessary for a force to be applied physically in order to bring about such change? Would the motion of the body change if it was subjected to a balanced force? Arrive at a suitable explanation for how a force could bring about changes in a body’s state of rest or motion.

Let us begin by understanding what is the general meaning of a force following which we shall look at how a force can affect the motion of a body.
Force is defined as any interaction that will change the state of rest or motion of a body. It is intuitively described as a push or a pull that is directed towards or away from a body. Physically, it is a vector quantity having both magnitude and direction and is directed along the line of action/application of the force.
A body experiences a force-induced change of state if the force acting on it is unopposed. This means that if two equal forces are acting on a body in opposite directions, the net force acting on the body will be zero, and will not produce any change in the state of rest or motion of the body. Such forces are called balanced forces. The change in the state of a body is thus brought about by unbalanced forces.
Let us now look at how force affects the motion of a body. Motion is defined as the change in position with respect to time. In such a case, notion is brought about by a force by either changing the speed of the body or changing the direction of a moving body. Thus a force can make a resting body move, or make a moving body come to a rest, or change the speed of the moving body or change the direction in which the body is initially moving.
This change in velocity of a body over time is nothing but the acceleration a of the body, due to the force F acting on it. This is given by the equation:
$F = ma$, where m is the mass of the body.
Thus, a force is basically responsible for the change in state of rest or motion of a body that is brought about by changing its velocity at a certain rate with time.

Note:
Note that the whole idea of force that we explored above is the basis of Newton’s Laws of Motion. The first law states that a body continues to remain in its state of rest or motion unless acted upon by a net external force. This means that if the net force on a body is zero, then the velocity of the body remains constant, i.e.,
$\Sigma F =0 \Rightarrow \dfrac{dv}{dt}=0 \Rightarrow a=0$
$\Rightarrow F=ma$
Newton’s second law states that the rate of change of momentum of a body with time is directly proportional to the force applied. This can be derived from the first law:
$F = ma \Rightarrow F = m.\dfrac{dv}{dt} = \dfrac{mdv}{dt} = \dfrac{dp}{dt}$, where p is the momentum of the body.
Newton’s third law states that every action warrants an equal and opposite reaction. If we exert a force F on an object, the object will exert a force on us, equal in magnitude but opposite in direction. Thus, if two forces acting on a body are equal and opposite there will be no net force acting on the body and it retains its state of rest or motion.