# Motion_ Speed _ Velocity by zhangyun

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```									Intro to Motion
Chapter 2.1-2.4
Standard 1a

Students know how to solve
problems that involve constant speed
and average speed.
Aristotle & Motion
Aristotle (384-322 BC), a Greek
scientist believed in two types of
motion, natural and unnatural
Natural motion: Motion directed up
or down (ex: boulders and smoke)
Unnatural motion: Motion created by
force (ex: push or pull)
With natural motion, heavy things
fall faster than light things
Galileo & Motion
Galileo (1564-1642) disproved
Aristotle by a famous experiment.
At the top of the leaning Tower of
Pisa, Galileo dropped a heavy object
and light object…
Both hit the ground at the same
time.
Galileo & Motion
Galileo also discovered that force is
NOT required to KEEP an object
moving, only to START it.
He rolled a ball on two inclined
planes. (like a skating half-pipe)
Galileo & Motion
Inertia: The tendency of anything to
remain as they are. If moving, they
tend to remain moving. If at rest,
they tend to stay at rest.

Force can change motion or rest.

Quick Think
How did Aristotle explain motion?

What did Galileo’s inclined plane
experiment prove?

A ball rolling on a pool table slowly
comes to a stop. How would Galileo
explain this?
Galileo & Motion
Galileo was first to measure speed.
Speed: distance covered per unit of
time.
Speed = Distance/Time
Ex: A horse covers 20km in a time of
1 hour, what is the speed?
20 km/h
Constant v. Average Speed
Constant Speed: Speed is the same
at a given time
Average Speed: Total distance
traveled over time
Speed v. Velocity
Velocity: Speed with direction
Ex: A car travels at 60mph in a
circle.
Is the speed constant?
Is the velocity constant?
Quick Think
What is the speed of a cheetah that
sprints 100m in 4 seconds? What