Mr Kwan
Inertia and Newton’s 1st Law
15th Nov, 2009
S4, physics
Led Ss to conclude that
“Constant v needs
nothing (no F)”
Tested new hypothesis
using small bearing
released from rest
on a smooth toy track
Asked Ss to provide
a new hypothesis
(constant v needs no F) …
and tested new hypothesis
using air track
Consolidated the idea
with video from NASA
Introduced Aristotle’s
belief/hypothesis
(constant speed requires
constant force)
Tested Aristotle’s belief
using air track
demonstration
Introduced
the concept
of inertia and mass
Ss experience the process of a typical scientific investigation
using well-known historical science stories
Introduced Aristotle’s belief…
“…this old man said…”:
Constant speed motion requires
constant force
Aristotle
(384 BC – 322 BC)
1
Testing Aristotle’s hypothesis
- Air track demonstration 1
Function of air track:
Air coming out from the holes on its surface to reduce friction,
similar to 歡樂天地氣墊球
T: If it is accelerating, that means it moves faster and faster.
However, do you think this is moving faster and faster ?
You didn't ........this one [pointing to the rider on the air
track] do you think it's moving faster and faster?
S: No, not faster ............. it is just forward.
T: It is not accelerating. Just a forward motion, then, it
becomes?... Constant velocity. OK, wait a minute…
Hey, [T drawing Ss’ attention to the s-t graph on the screen]
the displacement against time graph is a straight line.
So, What's the meaning of this straight line ? How is the
velocity changing in this way?
S: Constant ...
T: Constant velocity [T repeating S’s response]…
Displacement against time graph. It's the time ... constant
velocity……..constant velocity forwards, constant velocity
backwards.
2
Concluding that Aristotle’s hypothesis is wrong
T asked Ss to provide a new hypothesis
(constant velocity needs no force)
Kwan- provide new hypothesis
3
Tested the new hypothesis using another set up using a toy air track – similar to
Galileo's ‘thought’ expt
Constant speed motion requires
nothing (no force)
Galileo Galilei
(1564 - 1642)
Implicit vs explicit approach
Ss experience testing of hypotheses
proposed by great scientists (Aristotle
and Galileo)
Kwan sir – implicit or explicit approach?
4
Explicitly help Ss to link their experience to the typical
steps of scientific investigation
Typical steps
Students experience
Observation
Making Hypothesis
Collecting data to test
hypothesis
(experiment/observation)
Analysis
Drawing conclusion
Explicitly help Ss to link their experience to the typical
steps of scientific investigation
Typical steps
Students experience
Observation
Daily life observation, objects naturally slow down
(Aristotle)
Metal bob moves to the same height when released
(Galileo thought inspired by pendulum motion)
Making Hypothesis
Constant motion needs constant force (Aristotle)
Constant motion needs no force (Galileo)
Collecting data to test
hypothesis
(experiment/observation)
Observation of motion of objects on a lab air track
assisted by dataloggers
Observation of a metal ball moving along a toy air track
(such set-ups not available in Aristotle or Galileo’s time)
Analysis
Analysis of s-t graphs
Drawing conclusion
Constant motion needs constant force
Constant motion needs no force
5
Other aspects of NOS that could be
discussed using the historical development
Science is based on empirical evidence.
Scientific knowledge is subject to change. Even wellestablished scientific knowledge can be refuted or modified
upon new evidence. However, the shift of people’s belief
from old concepts to new concepts may take time.
Reasonable skepticism and the courage to challenge
authority often leads to new scientific knowledge
Experiments are not always feasible or necessary, logical
deduction as for Galileo can also contribute to scientific
advances
6