8.3 Scientific Investigation and Reasoning. The
student uses critical thinking, scientific
reasoning, and problem solving to make informed
decisions and knows the contributions of
relevant scientists. The student is expected to:
(D) relate the impact of research on scientific
thought and society, including the history of
science and contributions of scientists as related
to the content.
8.6 Force, motion, and energy. The student knows
that there is a relationship between force,
motion, and energy. The student is expected to:
(C) investigate and describe applications of
Newton’s law of inertia, law of force and
acceleration, and law of action-reaction such as in
vehicle restraints, sports activities, amusement
park rides, Earth’s tectonic activities*, and
*Will be covered in 3rd
• One of the most influential scientists of all
• English physicist, mathematician,
astronomer, natural philosopher,
alchemist, and theologian
• Invented a reflecting telescope, which
brought him much fame and attention
• Wrote Principia Mathematica, one of the
most influential science books in history
(discusses universal gravitation and laws of
An object at rest tends to stay at rest and an
object in motion tends to stay in motion
with the same speed and in the same
direction unless acted upon by an
Also called the law of inertia.
• In other words an object will keep doing
whatever it’s doing (still or moving)
unless an unbalanced force acts on it.
• Example: Your skateboard will stay lying
in the driveway until someone moves it.
And, if your skateboard suddenly hits a
curb and stops short… you will keep
moving until something stops you!
• Newton’s 1st
law is also known as the Law
of Inertia.Inertia. (Inertia is an object’s(Inertia is an object’s
tendency to resist a change intendency to resist a change in
• The greater an object’s mass, the greaterThe greater an object’s mass, the greater
its inertia, and the larger the force neededits inertia, and the larger the force needed
to overcome the inertia.to overcome the inertia.
•Which vehicle would
take longer to stop?
•It will take longer for
the dump truck to stop
than the car, because the
dump truck has more
A property of
of an object to
change in its
The greater the
The greater the
All About Inertia
Examples of Newton’s
• car suddenly stops and you strain against the seat
belt because our bodies want to keep moving
• when riding a horse, the horse suddenly stops and
you fly over its head
• the difficulty of pushing a dead car
• car turns left and you appear to slide to the right
• ketchup stays in the bottom (at rest) until you bang
(outside force) on the end of the bottom
• a headrest in a car prevents whiplash injuries during
a rear-end collision (your head goes forward and then
Law and You
Don’t let this be you. Wear seat belts.Don’t let this be you. Wear seat belts.
Because of inertia, objects (includingBecause of inertia, objects (including
you) resist changes in their motion. Whenyou) resist changes in their motion. When
the car going 80 km/hour is stopped bythe car going 80 km/hour is stopped by
the brick wall, your body keeps moving atthe brick wall, your body keeps moving at
80 m/hour.80 m/hour.
Second law: The
greater the force
applied to an object,
the more the object
will accelerate. It
takes more force to
accelerate an object
with a lot of mass
than to accelerate
something with very
little mass. The player in black had
more acceleration thus he
hit with a greater amount
The greater the force, the greater the
The greater the mass, the greater the
force needed for the same acceleration
Calculated by: F = ma
(F = force, m = mass, a = acceleration)
Newton’s 2nd Law proves that different masses
accelerate to the earth at the same rate, but with
• We know that objects
with different masses
accelerate to the
ground at the same
• However, because of
Law we know
that they don’t hit the
ground with the same
F = maF = ma
98 N = 10 kg x 9.8 m/s/s98 N = 10 kg x 9.8 m/s/s
F = maF = ma
9.8 N = 1 kg x 9.89.8 N = 1 kg x 9.8
Examples of Newton’s 2nd
• hitting a baseball, the harder the hit, the
faster the ball goes
• accelerating or decelerating a car
•The positioning of football players –
massive players on the line with lighter
(faster to accelerate) players in the
• a loaded truck versus an unloaded truck
• For every action force, there is an
equal and opposite reaction force.
(Forces are always found in pairs.)
• Athlete pushes bar upwards.
• Bar pushes the athlete downwards.
• Bowling ball pushes pin to the right.
• Pin pushes bowling ball to the left.
Reaction of a rocket. FuelsReaction of a rocket. Fuels
are burned in the engine,are burned in the engine,
producing hot gases.producing hot gases.
The hot gases push againstThe hot gases push against
the inside tube of the rocketthe inside tube of the rocket
and escape out the bottom ofand escape out the bottom of
the tube. As the gases movethe tube. As the gases move
downward, the rocketdownward, the rocket
moves in the oppositemoves in the opposite
•Momentum of the car moving forward and the
car comes to a sudden stop, our body pushes
against the seat (action) belt and the seat belt
pushes back (reaction).
•When you lean on the wall to rest, the weight
on the wall provides the reaction force and the
wall pushes back on you (reaction force) with
the same force.
• Roller coaster ride- The train to the tracks.
•Birds wings to the air.