Transcript (Newton`s) Second Law of Motion

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 = 1kg•m/s2
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
m a
Calculations Using Newton’s
Second Law of Motion
F = ma
 As the result of a serve, a tennis ball (mt
= 58 g) accelerates at 430 m/s2 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/s2)
 The force of gravity (N = 10 kg•m/s2) 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 = 1kg•m/s2
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 = 1kg•m/s2
Free-Body Diagram
Adding Vectors

What is a scalar? Examples?

What is a vector? Examples?
Adding Vectors

30 N
40 N

30 N
40 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