Bruce Campbell chapter 3

1. Aristotle on Motion
• Greeks developed ideas of science that
force causes motion.
• Two types of motion: Natural and
Violent
• Violent
• Natural is straight up or straight down
• Violent is the result of a force that is
pushed or pulled.

2. Copernicus and the Moving
Earth
 Determined that the simplest way to interpret
astronomical observations was to assume Earth and
other planets move around the sun.
 Most believed that the Earth was at the center of the
universe not the sun.
 Copernicus was prosecuted for his thoughts.

3. Galileo on Motion
 Italian scientist
 Supported Copernicus ideas.
 Did not believe that force is necessary to keep an object
moving.
 Friction: The name of force where two materials touch as
they move past each other.
 Concluded that two inclined planes facing each other
will roll a ball back and forth.
 Inertia=the property of a body to resist changes to its
state of motion.

4. Newton’s Law of Inertia
 Changed the Aristotelian ideas that had dominated for
2000 years.
 Developed famous laws of motion.
 Law of Inertia=restatement of Galileo’s idea that a force
is not needed to keep an object moving.
 Every object continues in a state of rest, or uniform speed
in a straight line, unless acted on by a nonzero net force.

5. Objects at Rest
 Things that tend to keep on doing what they are
already doing.
 Dishes on a tabletop are in a state of rest.
 Only a force will change their state of rest.
 Dishes moving if a tablecloth is ripped out from under
them.

6. Objects in Motion
 When there is more friction, the object has less of a
chance to move.
 A hockey puck hit on the street will move less than
one hit on ice or an air hockey table.
 An object tossed in space will move forever by
virtue of its own inertia.
 Ancients thought that continual forces were needed
to maintain motion.
 Objects continue to move by themselves.

7. Isaac Newton
 At 24 years old he laid the foundations for physics.
 Established himself as a first rate mathematician.
 Elected to the Royal Society, where he exhibited the world’s
first reflector telescope and made with his own hands.
 Wrote one of the greatest scientific books ever written, the
Principia Mathematica Philosophiae Naturalis.
 Elected into Parliament
 Knighted by Queen Anne and buried at Westminster Abbey.
 His ideas and insights changed the world and elevated the
human condition.

8. Mass-A Measure of Inertia
• The more mass an object has, the greater its inertia
and the more force it takes to change its state of
motion.
• Kick an empty soda can it goes a distance.
• Kick a soda can filled with sand and it won’t go as far.
• The amount of inertia an object has depends on its
mass-the amount of material in the object.

9. Mass is not Volume
 Do not confuse mass and volume
 Volume is a measure of space and is measured in
units.
 Mass is measured in the unit of kilograms.
An equal size bag of cotton balls and nails have equal
volumes but not equal mass.

10. Mass is Not Weight
 Mass is often confused with weight.
 Mass is a measure of the amount of material in an
object and depends only on the number of and kind
of atoms that compose it.
 Weight is a measure of the gravitational force acting
on the object

11. Mass is Inertia
 The amount of material in a stone is the same no
matter on earth, space or the moon.
 The weight of the stone would be very different on
earth, the moon or space.
 Mass is the quantity of matter in an object.
 Weight is the force of gravity on an object.

12. One Kilogram Weighs
10 Newtons
 In the US it is common to describe matter in an
object by its weight.
 In most other parts of the world it is common to
describe matter in units of mass.
 SI is the unit of mass.
 The SI unit of force is the newton.
 Weight and mass are proportional to each other.

13. Objects Move With Earth
 The law of inertia states that objects in motion
remain in motion if no unbalanced forces act on
them.
 All objects move as the earth does too.
 If you are jumping off a step to go straight down to
pick up a ball, all objects are moving at the same
time, so you are able to go straight down and
nothing.

14. Objects Move
With Vehicles
 The vertical force of gravity affects only the vertical
motion of a coin.
 If you flip a coin while in a fast traveling car, train or
plane the coin will keep up with us because of the law of
inertia.
 Aristotle did not recognize the idea of inertia.
 He imagined that there were different laws for motion
on earth and in space.
 Galileo and Newton thought the same rules for all
moving objects requiring no force to keep moving if
friction was not present.