"An object at rest remains at rest and an objet in motion remains in motion at constant speed in a straight line unless acted on by an unbalanced force."
Newton's first law of motion describes the major concept of inertia. Inertia is an object's resistance to changes in motion. Isaac Newton found that objects will only change motion when unbalanced forces act upon it. This means that the pushes or pulls on something is unequal to its opposite. Otherwise, everything in the universe will remain still or travel in the same direction at the same speed forever. Objects will stop moving by the resistance of things such as the ground or air.
This diagram shows that balanced forces cause resting objects to stay at rest because they have a constant velocity of 0 m/s, and therefore an acceleration of 0 m/s/s. When an object does not change speed or direction, it will stay at rest forever. However, objects in motion do not have a velocity of 0 m/s. If the forces are still balanced, it will be moving with speed in a straight line but not changing velocity. In other words, the acceleration is 0 m/s/s. The balanced forces acting on an object in motion mean that object will stay in motion forever, unless another unbalanced force is exerted on it.
A real life example of Newton's first law is like a bowling ball hitting the pins. The law states that an object at rest will stay at rest until an unbalanced force acts on it. This is like the pins. The pins stay idle on the lane until the ball hits them. Additionally, the second part of the law also states that moving object will continue moving forever at the same speed until an unbalanced force acts on it. This is like the bowling ball. The rolling ball hits the pins and creates an unbalanced force which will cause the pins to move because the pushing force of the ball was greater than the pins' resting force. Although the ball had been traveling at a consistent rate, its speed was altered when it came in contact with the stationary pins.