Transcript forces and the laws of motion - PAMS-Doyle

Newton’s Laws
• 1665 – 1666 Isaac Newton
developed 3 laws of motion.
• Inertia – the tendency of
objects to remain in motion
or stay at rest. Related to
mass: bigger object =
harder to move or stop.
• You MUST memorize all
three laws of motion and the
examples that go with them!
Law # 1
• 1st law – an object at rest
will remain at rest; an
object in motion will remain
in motion; at constant
velocity unless acted upon
by an unbalanced force.
• Example: you’re in a car
moving 45 mph and you
have to slam on the brakes;
the car stops but you keep
moving forward.
Inertia and Gravity: Why the
planets revolve around the sun
Law # 2
• Force (1 N) = Mass (kg) x Acceleration
• Acceleration = Force/Mass
• Measured in 1 N = 1 kg * 1 m/s2
• A greater force is needed to
accelerate an object with greater
inertia.
• Example: How much force is
needed to accelerate a 1400 kg car
2m/sec/sec?
1400 x 2 = 2800 N
Force = mass * acceleration
Law #3
• 3rd law – For every
action, there is an equal
and opposite reaction.
All forces come in pairs.
• Examples: walking (you
push down and back but
you move up and
forward); a rocket (it
moves up with the same
force that is released out
the bottom of it in the
opposite direction).
Action-Reaction
Momentum
• Momentum Mass * Velocity
• Measured in kg•m/s
• Law of conservation of momentum the total
momentum of any group of objects remains the
same unless outside forces act on the objects.
• Friction is an example of an outside force
Time to continue…….
Which law?
Which of Newton’s Laws apply?
Gravity
• Galileo –He dropped two cannon balls, one was
10 x the mass of the other, he wanted to prove
that they would both hit the ground at the same
time. He was right.
• When the only force acting on a falling object is
gravity, they are in free fall.
• Acceleration of a falling object is due to the force
of gravity is 9.8 m/sec/sec.
• 1 meter = 9.8 m/sec/sec
• 2 meters = 19.6 m/sec/sec
• 3 meters = 29.4 m/sec/sec
Then why doesn’t everything fall
at the same rate?
• Air resistance – terminal
velocity, force of air/gravity
becomes balanced.
• In simple terms: there is a
balance between gravity pulling
you and the air holding you
up…
Do you feel like movin??