balanced forces
Balanced forces are two forces acting on an object that are equal in size and opposite in direction. When the forces are balanced, the object will remain at rest or continue moving at a constant velocity.

force
A force is a push or pull that can cause an object to move, stop, or change its speed or direction. Forces can be exerted by objects in contact with each other, such as a person pushing a box, or by objects not in contact, such as gravity pulling an apple towards the ground.

unbalanced forces
Unbalanced forces are forces that are not equal in size and opposite in direction. When unbalanced forces act on an object, they cause a change in the object's motion, such as accelerating, decelerating, or changing direction.

inertia
Inertia is the tendency of an object to resist changes in its motion. An object at rest will stay at rest, and an object in motion will stay in motion at a constant velocity unless acted upon by an external force. The greater the mass of an object, the greater its inertia.

Newton's first law of motion
Newton's first law of motion states that an object will remain at rest or in motion at a constant velocity unless acted upon by an external force. This is also known as the law of inertia. The first law explains the behavior of objects when no external forces are acting on them, and it is the foundation of classical mechanics.