Transcript Newton`s Laws - Dr. Robert MacKay

Newton's Laws of Motion
Dr. Robert MacKay
Clark College, Physics
Introduction
• Newtons 3 laws of motion
• 1. Law of inertia
• 2. Net Force = mass x acceleration
•
(F=MA)
• 3. Action Reaction
• Newton’s Universal Law of Gravity
Newton came up with these laws in about 1670 to describe the motion of
the planets around the sun. These fairly simple rules explained planetary
motion extremely well. This was a problem scientists had struggled with
for thousands of years with no success. These same laws apply to
anything that moves including the atmosphere and winds.
Isaac Newton 1642-1727
Isaac Newton 1689
Knighted by Queen Anne 1705
Isaac Newton 1702
Isaac Newton 1726
• To understand Newton’s laws of motion
one must first understand velocity.
• The velocity of an object is related to how
fast an object is moving and in what
direction. Your velocity changes any time
that your speed changes or your direction
changes (or both).
• Next we need to understand what we mean by acceleration.
• The acceleration of an object describes how fast its velocity
changes.
• If an object travels in a straight line with constant speed the
acceleration is zero.
• Whenever an object either changes speed of changes direction it
is accelerating.
• In the metric system acceleration is expressed in term of meters
per second (m/s) increase over each second (s). For example is
a car speeds up from 0 to 20 m/s speed in 4.0 s its acceleration is
5.0 m/s each second (5 m/s2)
Law of inertia (Newton’s 1st Law)
• Every object continues in its state of rest, or of
uniform motion in a straight line, unless it is
compelled to change that state by forces impressed
upon it.
• acceleration = 0.0 unless the objected is acted on by
an unbalanced force
• Example: When the Coriolis force exactly balance
the pressure gradient force the wind travels in a
straight path at constant speed.
Newton’s 2nd Law
• Net Force = Mass x Acceleration
•
Net_F = M A
• The metric system unit for Force is a
Newton (N). A force of 1.0 N is required to
accelerate a 1.0 kg object at a rate of 1.0
m/s2.
Newton’s 2nd Law
• Net Force = Mass x Acceleration
• F=MA
M=2.0 kg
A= 6.0 m/s2
F=?
F=M A
= 2.0 kg x 6.0 m/s2
=12.0 Newtons
= 12.0 N
An object experiences a net force and exhibits an acceleration
in response. Which of the following statements is always true?
(a) The object moves in the direction of the force.
(b) The acceleration is in the same direction as the velocity.
(c) The acceleration is in the same direction as the force.
(d) The velocity of the object increases.
An object experiences a net force and exhibits an acceleration
in response. Which of the following statements is always true?
(a) The object moves in the direction of the force.
(b) The acceleration is in the same direction as the velocity.
X(c) The acceleration is in the same direction as the force.
(d) The velocity of the object increases.
Newton’s 2nd Law
• Net Force = Mass x Acceleration
• F=MA
M=2.0 kg
A= ?
F=6.0 N
A=F / M
= ? m/s2
Newton’s 2nd Law
• Net Force = Mass x Acceleration
• F=MA
M=2.0 kg
A= 3.0 m/s2
F=6.0 N
A=F / M
= 3.0 m/s2
Newton’s 2nd Law
• Net Force = Mass x Acceleration
• F=MA
M=?
A= 20.0 m/s2
F= 10.0 N
M= F/A
= ? kg
Newton’s 2nd Law
• Net Force = Mass x Acceleration
• F=MA
M=?
A= 20.0 m/s2
F= 10.0 N
M= F/A
= 0.50 kg
Newton’s 2nd Law
• Net Force = Mass x Acceleration
• F=MA
M= 5.0 kg
F= 150.0 N
D =120.0 N
A= ? m/s2
Net Force = ?
Newton’s 2nd Law
• Net Force = Mass x Acceleration
• F=MA
M= 5.0 kg
F= 150.0 N
D =120.0 N
2. A= 6.0 m/s2
1. Net Force = 30.0 N