State and explain the Newton's first law of motion.
Newton's First Law
Newton's First Law of Motion explains how inertia affects moving and non-moving objects. Newton's first law states that an object will remain at rest or move at a constant speed in a straight line unless it is acted on by an unbalanced force. Inertia comes from mass. Objects with more mass have more inertia.
To understand inertia, imagine moving a bowling ball and a golf ball that are at rest. The golf ball has a mass of 0.05 kilogram, and the bowling ball has a mass of five kilograms. The bowling ball has 100 times more mass than the golf ball, so it has 100 times more inertia, too.
Now ask yourself, which needs more force to start moving? If you push for the same distance, the bowling ball takes much more force to get it moving the same speed as the golf ball. The bowling ball needs more force because a bowling ball has more inertia than a golf ball. The greater an object's inertia, the greater the force needed to change its motion.
According to Newton's first law, an unbalanced force is needed to move the book on your desk. You could supply the force by pushing the book.
An unbalanced force is needed to change the speed or direction of the spacecraft. This force could be supplied by the spacecraft's engines.
Because of inertia, an object at rest will remain at rest until something causes it to move. Likewise, a moving object continues to move at the same speed and in the same direction unless something acts on it to change its speed or direction.