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Newton's Second Law of Motion

You've already learned about Newton's First Law. This law is used to predict the motion of objects when no net force (unbalanced force) is acting on the object. You know that objects in motion continue in motion at a constant velocity according to this law and that objects at rest stay at rest.

But, what about objects that do have unbalanced forces acting on them? What can be used to predict their motion? That's where Newton's Second Law comes in.

Newton's Second Law deals with changes in an object's motion based on unbalanced forces acting on the object. It deals specifically with an object's acceleration, which is affect by both the mass and the force acting on the object.

Newton's Second Law states that acceleration is produced on an object when an unbalanced force acts on the object. This acceleration depends on both the object's mass and the force applied to the object. Let's look at how the force and mass affect an object's acceleration.

Force

  • You should realize that the greater the force, the greater the acceleration will be. For example, the harder (more force) I use to throw a baseball, the faster it will travel.
  • Acceleration is directly proportional to force. (That means as force increases so does acceleration)

    baseball player

Mass

  • If I throw a baseball and a bowling ball with the same force, which will have a greater acceleration?

    a bowling ball and a baseball

    Answer: The baseball, of course!
  • As the above question shows, mass also affects acceleration. The greater the mass, the harder it will be to cause an object to accelerate. Therefore, more force will need to be applied.
  • Acceleration is inversely proportional to mass. (That means as mass increases, acceleration decreases)

The next section of the lesson will look at how the concepts in Newton's Second Law are related in a math equation – probably one you are already familiar with. Before moving on, review Newton's Second Law: