Why don’t objects in motion continue moving forever?
Objects in motion do not continue moving forever mainly because of the presence of external forces that act upon them. According to Newton's first law of motion, an object at rest tends to stay at rest, while an object in motion tends to stay in motion with the same speed and direction unless acted upon by an external force.
Some of the common external forces that act upon objects in motion are friction, air resistance, and gravity. Friction, for example, opposes the motion of objects when there is contact between surfaces, gradually slowing them down. Air resistance is another form of friction that acts against the motion of objects in the presence of air or fluid medium, such as when a moving object encounters air particles and experiences drag. Gravity, which is a fundamental force of nature, also affects the motion of objects by pulling them towards the center of the Earth or any other massive object, causing them to accelerate and eventually come to a stop or change their trajectory.
Moreover, if no external forces were acting on an object, it would encounter internal forces such as molecular interactions or energy losses due to factors like heat or sound, which would eventually cause it to lose energy and eventually come to rest.
In practical terms, the absence of an ideal frictionless environment and the presence of various external forces result in the gradual loss of energy or the conversion of energy into different forms, leading to objects in motion eventually coming to a stop.