Physics 10
Physics 10
Newton’s 1st Law
Aristotle
Galileo
Newton
Exercise 14
Exercise 18
Aristotle (384 – 322 BC)
⇒ Aristotle believed that
there were two kinds of
motion: natural motion and
violent motion.
Natural Motion - motion of objects toward
their natural places.
Violent Motion - motion due to contact with a
mover or agent.
⇒
Any object will move towards its natural
place (natural motion) and remain there at rest
provided it is not prevented from doing so, or
removed from it by a forced movement (violent
motion).
⇒
All terrestrial objects were made up of a
combination of four elements: earth, water, air,
and fire.
⇒
All celestial objects were made up of
quintessence.
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⇒ The “natural motion” of earth and
water was downward towards the earth.
⇒ The “natural motion” of air and fire
was upward towards the sky.
⇒ The “natural motion” of quintessence
was circular.
⇒ Aristotle believed that heavier objects
were made up of more “earth”.
⇒ Aristotle therefore concluded that
heavier objects strive towards their natural
place (the earth) faster than lighter objects.
⇒ This was later (2000 years later!)
proved wrong by Galileo.
Galileo Galilei (1564 – 1642)
⇒
A ball rolling down an
inclined plane picks up speed.
⇒
A ball rolling up an inclined
plane loses speed.
⇒ Galileo used inclined planes to study the
motion of various objects.
⇒
Therefore a ball rolling on a
flat surface should not change its
speed at all.
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⇒ “If I have a long horizontal plane,
⇒
A ball always rolls up the inclined plane to
almost exactly its initial height. (Without
friction, it would roll up the incline to exactly its
initial height.)
Isaac Newton (1642 – 1727)
how far must the ball go to reach the
same height?”
Answer: Forever!
Exercise 14
In terms of Newton’s first law (the law
of inertia), how does a car headrest help
guard against whiplash in a rear-end
collision?
⇒ In a car at rest, your head tends to stay at
rest. When the car is rear ended, the car
lurches forward and if the headrest isn’t
there, tends to leave your head behind. Hence
a neck injury.
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Exercise 18
Each bone in the chain of bones forming your spine is
separated from its neighbors by disks of elastic tissue.
What happens, then, when you jump heavily on to your
feet from an elevated position? Can you think of a
reason why you are little taller in the morning than the
night before?
⇒ An object in motion tends to stay in motion,
hence the disks tend to compress upon each other.
This compression results in people being slightly
shorter at the end of the day than in the morning.
At home activity:
Before going to bed tonight, find a
point that you can almost reach up to.
Then in the morning, try to reach that
point again. You should find that you
can easily reach it in the morning.
Try it and see!
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