Transcript Newton`s Laws of Motion

Newton’s Laws of Motion
Dynamic dynamics and
unexpected returns
Chapter 3
Sir Isaac Newton
• Determined many
physical laws based
on mathematics.
• His book, Principia,
revolutionized the
fields of both
science and
mathematics
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
– Dependent on mass
Newton’s 1st Law of Motion
Which has more inertia?
1. An empty dump truck
2. A full dump truck
Which has more inertia?
1. A quarter
2. A dime
Which has more inertia?
1. A freight train
2. A full dump truck
Which has more inertia?
1. A freight train
2. A cargo plane
Which has more inertia?
1. An empty dump truck going 170 km/h
2. 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
Newton’s 2nd Law of Motion
What is the force applied by a
mass of 2 kg with an acceleration
of 6 m/s2?
1. 6 N
2. 3 kg●m/s
3. 12 kg●m/s2
What is the acceleration of a
mass of 6 kg applying a force of
24 N?
1. 4 m/s2
2. 144 m/s2
3. 0.25 m/s2
What is the force applied by the
acceleration of a 3.5 kg mass to
7 m/s2?
1. 2 N
2. 24.5 kg●m/s2
3. 0.5 kg ●m/s2
What mass is required to apply a
force of 28 N after an
acceleration of 7 m/s2?
1. 196 kg
2. 4 kg
3. 0.25 kg
What acceleration would cause a
12 kg mass to produce a force of
90 kg●m/s2?
1. 7.5 N
2. 7.5 m/s
3. 7.5 m/s2
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 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?
1. 122,616 N
2. -122,616 N
3. 0 N
What would the net force be if two
players kick a soccer ball from opposite
directions according to the diagram?
1. 60 N, to the left
2. 60 N, to the right
3. 0 N
4. 180 N, upwards
What would the net force be if
you pushed a hockey puck with
200 N?
1. 0 N
2. 200 N against the push
3. 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
Newton’s 3rd Law of Motion
Good Examples
• Rocket engines
• Firing a gun
• Jumping off of a johnboat
Forces and Vectors
Gravity
• Gravity is a force of attraction between
all objects of mass.
• Depends on:
– the distance between the masses
• “inverse square” law
– the size of the masses
• Often as a percentage of the whole
Weight
• Weight is the force of attraction caused
by gravity acting on a mass.
Fw = m•g
• The g means local gravity
– on Earth, g = 9.8m/s2
Gravity
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?
1. 245 N
2. 2.6 N
3. 0.392 N
If an object weighs 397 N, what
is its mass?
1. 0.02 kg
2. 3890.6 kg
3. 40.5 kg
If an object weighs 1100 N but
has a mass of 125 kg, which
planet is it on?
1. Venus, g = 8.8 m/s2
2. Mars, g = 3.7 m/s2
3. Jupiter, g = 24.8 m/s2
Friction
• Friction is the force that opposes all
motion.
• A moving object will always lose energy
to friction
Types of Friction
• Sliding Friction
– When two surfaces slide along each other
– Most resistive friction
– Can lead to buildup of heat
Types of Friction
• Rolling Friction
– When an object or surface rolls along
another
– Less resistive than sliding, more resistive
than fluid
Types of Friction
• Fluid Friction
– When a surface slides along a fluid (gas or
liquid)
– Least resistive friction
• Lubrication
– Air resistance
What type of friction is
exhibited by your shoes on
the ground?
1. Sliding
2. Rolling
3. Fluid
4. Air Resistance
5. None of the above
What type of friction is
exhibited by a lubricant?
1. Sliding
2. Rolling
3. Fluid
4. Air Resistance
5. None of the above
What type of friction is
exhibited by the wheels on a
cart?
1. Sliding
2. Rolling
3. Fluid
4. Air Resistance
5. None of the above
What type of friction is
exhibited by your fingerprints?
1. Sliding
2. Rolling
3. Fluid
4. Air Resistance
5. None of the above
The Big “Mo”
• Momentum is the product of an object’s
mass multiplied by its velocity.
• p=m•v
• kg•m/s = kg • m/s
What is the momentum of a 210
kg hog running at 12 m/s?
1. 17.5 kg●m/s
2. 2520 kg●m/s
3. 0.057 kg●m/s
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
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.