Transcript newton*s laws

NEWTON’S
LAWS
NEWTON’S FIRST LAW
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AN
OBJECT IN
MOTION
STAYS IN
MOTION
Unless another force acts
upon it
This rider hasn’t had a
stopping force act on
him…. YET
NEWTON’S 1ST IN DIFFERENT WORDS
SO IF YOU THROW A BALL, WHY
DOESN’T IT JUST GO ON AND ON INTO
OUTER SPACE FOREVER?
• Friction forces occur as it passes through the air, causing it
to slow down
• Simultaneously, gravity forces are pulling it down to Earth
• Once it hits land, friction with the ground eventually causes
it to stop.
• If you threw it while in space where there is no friction or
strong gravity source nearby, it WOULD keep going on
forever
NEWTON’S SECOND LAW
Force = mass x acceleration
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BECAUSE THIS PLANE HAS SUCH A
HUGE MASS, THIS MAN’S FORCE
WON’T BE ABLE TO ACCELERATE IT
MUCH
THE GREATER THE FORCE, THE MORE
THE OBJECT CAN ACCELERATE
More mass= less acceleration
Less mass= more acceleration
PRACTICE PROBLEMS
• Force= Newtons
• Mass= kilograms
• Acceleration= m/sec2 (meters per second
squared which means meters per second
every second)
PRACTICE PROBLEM
• What net force is required to accelerate
a car at a rate of 2 m/s2 if the car has a
mass of 3,000 kg?
• ?= 3000 X 2
• FORCE = 6000 Newtons
NOW HALF THE MASS—HOW DOES
IT AFFECT THE FORCE?
• What net force is required to accelerate
a car at a rate of 2 m/s2 if the car has a
mass of 1500 kg?
• ?= 1500 X 2
• FORCE = 3000 Newtons
PRACTICE PROBLEMS
• An automobile with a mass of 1000 kilograms
accelerates when the traffic light turns green. If the
net force on the car is 4000 Newtons, what is the
car’s acceleration?
• 4000 = 1000 x ?
• 4 meters per second squared
NOW DOUBLE THE CAR MASS
• An automobile with a mass of 2000 kilograms accelerates
when the traffic light turns green. If the net force on the car
is 4000 Newtons, what is the car’s acceleration?
• 4000= 2000 x ?
• 2 meters per second squared
• DID YOU SEE HOW THE ACCELERATION WAS CUT IN HALF?
• Ronda Rousey’s (an MMA fighter) arm is 4.6 kg. If
she punches a guy in the face with an
acceleration of 40 meters/second2, how much
force will he feel?
• What if she doubles her acceleration to 80? m/s2 ?
• What if a much bigger man with an arm size of 8
kg throws the exact same punch?
• Why are there weight classes in boxing and MMA?
NEWTON’S 3RD LAW
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FORCES COME IN PAIRS AND
ARE OFTEN CALLED “ACTION”
AND “REACTION”
THEY ALWAYS EQUAL EACH OTHER
• Now, lightly push against the side of your table with your
pinky finger only.
• Now, push hard enough with your pinky to try to move the
table.
• Did you notice that the table pushed you back harder the
second time?
• What would happen if you pushed against a concrete wall
with just one pinky… I mean push with ALL YOUR WEIGHT
AND STRENGTH. How hard would the wall push back?
• It is likely that the force would be so great that you could
break your pinky finger
THESE FORCE PAIRS ARE ALWAYS
OPPOSITE IN DIRECTION
Though they are equal, they can
create movement
This is because the forces are
each acting on different objects