Transcript Newton`s Laws of Motion

Newton’s Laws of Motion
Force, gravity, projectiles,
friction, & momentum
Sir Isaac Newton
• Determined many physical laws based
on mathematics.
• His book, Principia, revolutionized the
fields of both science and mathematics.
• He did a great job of explaining effects
that seemed to have no causes.
Four Basic Types of Forces
• Gravity
• Electromagnetic
• Strong nuclear
• Weak nuclear
Newton’s First Law of Motion
• Inertia - An object at rest will remain at
rest, and an object in motion will
remain in motion unless acted upon by
an outside force.
How does mass
effect inertia?
Which has more inertia?
An empty dump truck
2. A full dump truck
1.
A quarter
2. A dime
1.
A freight train
2. A full dump truck
1.
Which has more inertia?
1. A freight train
2. A cargo plane
3. An empty dump truck going 170 km/h
4. A cargo plane sitting on the runway
Newton’s Second Law of Motion
• Force equals mass multiplied by
acceleration
• F = m•a
– Force is any push or pull that can affect
motion
– Mass in kg, acceleration in m/s2
– Newtons: 1N = 1kg•m/s2
What is the force applied by a
mass of 2 kg with an acceleration
of 6 m/s2?
a. 6 N
F
b. 3 kg●m/s
c. 12 kg●m/s2
m
a
What is the acceleration of a
mass of 6 kg applying a force of
24 N?
a. 4 m/s2
b. 144 m/s2
c. 0.25
m/s2
F
m
a
What is the force applied by the
acceleration of a 3.5 kg mass to
7 m/s2?
F
a. 2 N
b. 24.5 kg●m/s2
c. 0.5 kg ●m/s2
m
a
What acceleration would cause a
12 kg mass to produce a force of
90 kg●m/s2?
1. 7.5 N
F
2. 7.5 m/s
3. 7.5 m/s2
m
a
Balanced v. Unbalanced Forces
• Balanced forces are equal and opposite
on the same object
– Balanced forces result in NO acceleration
• Equilibrium
– Unbalanced forces are added geometrically
• The Resulting or Net Force (Fn) always results
in an acceleration
Showing “Equal and Opposite”
• The observer determines the direction
of motion
• Directions opposite that motion can be
considered NEGATIVE
• Because the direction is considered
negative, the forces can be considered
negative
What would the net force be if
you pushed against the wall with
122,616N?
a. 122,616 N
b. -122,616 N
c. 0 N
What would the net force be if two
players kick a soccer ball from opposite
directions according to the diagram?
60 N, to the left
b. 60 N, to the right
c. 0 N
d. 180 N, upwards
a.
What would the net force be if
you pushed a hockey puck with
200 N?
a. 0 N
b. 200 N against the push
c. 200 N in the direction of the push
Newton’s Third Law of Motion
• For every action, there is an equal and
opposite reaction
(These forces act on two different
objects, so they are not balanced forces.)
Which Law???
Which Law???
Which Law???
Which Law???
Which Law???
Gravity
• Any two masses exert an attractive
force on each other.
• Depends on:
– the distance between the masses
– the size of the masses
Gravity
With the upward force of the floor
equilibrium is attained and there is
no motion.
Without the upward force of the
hand there is not equilibrium of
forces and motion occurs.
Gravity on Earth
• A gravitational force exists between all
matter in the universe. This is a huge
range.
• The force of gravity on Earth pulls
down.
Projectiles
• Because of Earth’s
gravitational pull and their own
inertia, projectiles follow a
curved path due to horizontal
and vertical velocities. When
you release a ball, the ball
moves downward because of
gravity, but the horizontal
speed remains the same.
http://phet.colorado.edu/en/s
imulation/projectile-motion
• A thrown ball will land at the
same time as a dropped ball
because the velocity
components are independent.
Weight
• Weight is the force of attraction caused
by gravity acting on a mass.
Fweight = m X g
• The g means local gravity
Fw
• On Earth, gravity = 9.8m/s2
m
g
Weight v. Mass
• We use weight and mass
interchangeably because the only
comparison we have is the Earth’s
gravity.
• Weight will change based on local
gravity; NASA has to take this into
effect
How much does a 25 kg object
weigh in Newtons?
a. 245 N
Fw
b. 2.6 N
c. 0.392 N
Remember: gravity = 9.8m/s2
m
g
If an object weighs 397 N, what
is its mass?
a. 0.02 kg
Fw
b. 3890.6 kg
c. 40.5 kg
m
g
If an object weighs 1100 N but
has a mass of 125 kg, which
planet is it on?
Fw
a. Venus, g = 8.8 m/s2
b. Mars, g = 3.7 m/s2
c. Jupiter, g = 24.8 m/s2
m
g
Friction
• Friction is the force that opposes all
motion.
• A moving object will always lose energy
to friction.
3 Types of Friction
more
1. Sliding when solid objects
grind over each other
• puck and ice
2. Rolling wheels spinning on an
axle
• skateboards eventually roll to a
stop
less
3. Fluid liquids or gases slow the
motion of a solid
• wind resistance
• oil a squeaky hinge
• pushes a surfer
Friction of Unmoving Objects
Static friction results when the surfaces of two
objects are at rest relative to one another and a
force exists on one of the objects to set it into
motion relative to the other object.
https://www.youtube.com/watch?v=AX_lCOjLCTo
Under a microscope we see that materials that
feel smooth are rough. Areas where the bumps
of materials stick together are called microwelds
and are the source of friction.
Air Resistance
• The amount of air
resistance on an
object depends on
the speed, size,
and shape of the
object.
• There is no air
resistance in a
vacuum.
What type of friction is
exhibited by your shoes on
the ground?
a. Sliding
b. Rolling
c. Fluid
d. Air Resistance
e. None of the above
What type of friction is
exhibited by a lubricant?
a. Sliding
b. Rolling
c. Fluid
d. Air Resistance
e. None of the above
What type of friction is
exhibited by the wheels on a
cart?
a. Sliding
b. Rolling
c. Fluid
d. Air Resistance
e. None of the above
What type of friction is
exhibited by your fingerprints?
a. Sliding
b. Rolling
c. Fluid
d. Air Resistance
e. None of the above
The Big “Mo”
• Momentum is the product of an
object’s mass multiplied by its
velocity.
•p=m•v
• Momentum = mass X velocity
What is the momentum of a 210
kg hog running at 12 m/s?
Fpw
a. 17.5 kg●m/s
b. 2520 kg●m/s
c. 0.057 kg●m/s
m
g
v
Law of Conservation of
Momentum
• Momentum can not be created or
destroyed under normal circumstances
• Momentum can be changed from one
form to another
– Total momentum before a change must
equal total momentum after a change
• Ex. truck of gravel coming to a stop,
pieces of a dropped light bulb
Law of Conservation of
Momentum
• Formula
m1v1+m2v1 = m1v2+m2v2
Momentum Demonstrations
• https://www.youtube.com/watch?v=W9
EqU1_DXUw OR
https://www.youtube.com/watch?v=W9
EqU1_DXUw
• What if Earth stopped rotating?
https://www.youtube.com/watch?v=K0GxoJ_Pcg
Conservation of Momentum and
Newton’s Laws
• An untethered astronaut is stranded
away from his spaceship while working
on a satellite in space. The only
equipment he has is all the tools he was
using to repair the satellite.
• Write a short narrative of how you think
he can get back to his spaceship.