Evidence for Newton’s Second Law of Motion  Investigate Recap What happened as you kept pushing the different balls? How did the a change in force affect acceleration? How did a change in mass affect acceleration?

Vocabulary (Newton’s) Second Law of Motion – the acceleration of an object is directly proportional to the unbalanced force acting on it and is inversely proportional to the object’s mass; the direction of the acceleration is the same as the direction of the unbalanced force; F=ma Newton – the force required to make one kilogram of mass accelerate at one meter per second squared; 1 N = 1kgm/s 2

Where There’s acceleration, There Must Be an Unbalanced Force  What are some examples of forces?  ALL ACCELERATIONS ARE CAUSED BY SOME FORCE, AND ALL FORCES CAUSE ACCELERATION!!!

Calculations Using Newton’s Second Law of Motion  F = ma F ma

Calculations Using Newton’s Second Law of Motion  F = ma  As the result of a serve, a tennis ball (m t = 58 g) accelerates at 430 m/s 2 for the very brief time it is in contact with the racket What force is responsible for this acceleration? Could an identical force accelerate a 5.0 kg bowling ball at the same rate?

Calculations Using Newton’s Second Law of Motion  F = ma  A tennis racket hits a sand-filled tennis ball with a force of 4.0 N. While the 275 g ball is in contact with the racket, what is its acceleration?

Gravity, Mass, Weight, and Newton’s Second Law  The force that keeps us on the ground is gravity (g = 10 m/s 2 ) The force of gravity (N = 10 kgm/s 2 ) is also known as weight

Vocabulary Weight – the vertical, downward force exerted on a mass as a result of gravity; w = mg (Newton’s) Second Law of Motion – the acceleration of an object is directly proportional to the unbalanced force acting on it and is inversely proportional to the object’s mass; the direction of the acceleration is the same as the direction of the unbalanced force; F=ma Newton – the force required to make one kilogram of mass accelerate at one meter per second squared; 1 N = 1kgm/s 2

Balanced and Unbalanced Forces  In order to determine the motion of an object, all the forces acting on the object must be considered

Vocabulary Free-body Diagram – a diagram showing the forces acting on an object Weight – the vertical, downward force exerted on a mass as a result of gravity; w = mg (Newton’s) Second Law of Motion – the acceleration of an object is directly proportional to the unbalanced force acting on it and is inversely proportional to the object’s mass; the direction of the acceleration is the same as the direction of the unbalanced force; F=ma Newton – the force required to make one kilogram of mass accelerate at one meter per second squared; 1 N = 1kgm/s 2

Free-Body Diagram

Adding Vectors  What is a scalar? Examples?  What is a vector? Examples?

Adding Vectors  30 N40 N

WHAT DO YOU THINK NOW?  What is a force?  How will the same amount of force affect a tennis ball and a bowling ball differently?

Food for Thought  Most people can throw a baseball farther than a bowling ball, and most people would find it less painful to catch a flying baseball than a bowling ball flying at the same speed as the base ball. Explain these two situations in terms of Newton’s First Law of Motion Newton’s Second Law of Motion