Newton’s 2 nd Law Physics October 25/26

Objectives 1.State the relationship between acceleration, mass and net force 2.Evaluate how the relationship between acceleration, mass, and net force affect motion 3.State and explain Newton’s second law of motion 4.Solve using the equation F = ma

What is Newton’s 2 nd Law Topic Newton’s second law Facts The acceleration produced by a net force on an object is directly proportional to the magnitude of the net force, is in the same direction as the net force, and is inversely proportional to the mass of the object (Hewitt 60).

What!? Topic Let’s put Newton’s 2 nd Law in our own words Facts Force and acceleration are proportional and mass and acceleration are inversely proportional The equation is F = ma F = force (N) m = mass (kg) a = acceleration (m/s 2 )..

How about a little more clarification Topic What does F = ma tell us? Facts When mass is constant, Force and acceleration are directly proportional to each other –As force increases so does acceleration –As force decreases so does acceleration

How about a little more clarification Topic What does F = ma tell us? Facts When force is constant, Mass and acceleration are inversely proportional to each other –As mass increases, acceleration decreases –As mass decreases, acceleration increases

A little more clarification Watch the video to hear Newton’s 2 nd law one more time. Newton's Second Law Explained

Class Activity Explained page 59 Topic Why are more massive objects harder to move? Facts More massive objects have more inertia

Class Activity Explained page 59 Topic How is the mass of an object related to acceleration when force is constant? Facts Mass and acceleration are inversely proportional. –More mass means less acceleration –less mass means more acceleration

Class Activity Explained page 59 Topic If you want objects of different masses to have the same acceleration, what must you do? Facts You must apply more force to the more massive object

More Practice with Newton’s 2 nd law Topic How much force, or thrust must a 30,000 kg jet plane develop to achieve an acceleration of 1.5 m/s 2 ? Facts Known m = 30,000 kg a = 1.5 m/s 2 Unknown F Equation F = ma Solve F = (30,000kg)(1.5 m/s 2) 45,000 N

More Practice with Newton’s 2 nd law Topic What acceleration is produced by a force of 2000 N applied to a 1000 kg car? Facts Known F = 2000 N m = 1000 kg Unknown a Equation F = ma Solve F = ma 2000 N = (1000kg) a 1000kg = 1000kg 2 m/s 2 = a

Class work Please complete #3-7 on page 65 in the textbook

Closing Topic Suppose a cart is being moved by a force. If suddenly a load is dumped into the cart so that the cart's mass increases, what happens to the cart's acceleration? WHY? Facts

Homework DUE NEXT CLASS Read chapter 4 for review of the 2 nd law