Inertia explained to kids

Inertia is the resistance of any physical object to a change in its state of motion. It is the tendency of an object to keep moving in a straight line at a constant speed. This resistance to change is measured by an object's mass. The more massive an object is, the more inertia it has. Inertia is one of the basic laws of physics. It was first described by Sir Isaac Newton in his book The Principia. Newton's laws of motion are the foundation of classical mechanics. Inertia is the reason why it is difficult to start moving a heavy object or to stop a moving object. Inertia is also the reason why a passenger in a car feels a force when the car starts or stops. The force is equal to the mass of the object times the acceleration. The greater the mass of the object, the greater the force. Inertia is a property of all matter, not just of objects on Earth. It is a universal law of nature. All matter has inertia. Even the smallest particles of matter have inertia. Inertia is what keeps an object moving in a straight line at a constant speed. It is the tendency of an object to resist a change in its state of motion. The more massive an object is, the more inertia it has. Inertia is one of the basic laws of physics. It was first described by Sir Isaac Newton in his book The Principia. Newton's laws of motion are the foundation of classical mechanics. Inertia is also the reason why a passenger in a car feels a force when the car starts or stops. The force is equal to the mass of the object times the acceleration. The greater the mass of the object, the greater the force. Inertia is a property of all matter, not just of objects on Earth. It is a universal law of nature. All matter has inertia. Even the smallest particles of matter have inertia.