Newton’s first law
If an object is at rest , it will remain in that state unless applied by an unbalanced force. Similarly if an object is moving , it will remain in uniform motion unless applied by an unbalanced force.
Galileo introduced this theory in late 1500s. He said that objects have a natural tendency to return to their original positions if they are not being applied by a force. If a cycle is to be moved continuously, the person need to apply a force to the paddle. Descartes also said the same thing.
Newton however, disagreed with them. According to Newton;
“An object at rest remains at rest unless applied by an unbalanced force. An object in motion continues to move with the same speed and in the same direction unless acted upon by an unbalanced force”.
Hence, according to Newton an object maintains its state of motion until an unbalanced force is applied to it. It turned out that Newton was right. For instance a cycle keeps on moving unless its brakes are not applied. The brakes apply a force of friction to the tyre that cause it to stop.
Similarly gravitational force and the air resistance also acting on the tyre cause it to stop if one does not keep paddling. If these forces are made zero. then the cycle will keep on moving. there will be no need to paddle it then. In the same manner a book only rests on a table because the net force acting on it is zero.
Law of Inertia
Newton’s first law is also known as “the law of inertia”.
Inertia is the property of a body to resist change in its motion.
Lets say you are traveling in a car. Although with respect to the car you are at rest, but you are considered to be moving with respect to the environment. When the brakes are applied, the car may stop but you will tend to be pushed forward due to inertia since your moving body would resist the change in its motion.