Source Material for this week

1
Source Material for this week

• Monday (Lec 17) Energy Motion
• CP 4.1-4.3 (Motion, Conservation Laws)
• Wednesday Friday (Lecs 18 19)
• Keplers Laws from CP 3.3 (pp. 73-74 you skipped
  them before)
• CP 4.4 4.5 (Gravity Orbits)
• SKIP the section on Tides (Begin again at Why do
  all objects fall at the same rate?)

2
4. Energy and Motion

• What is energy?
• Terminology/types of energy
• Law of Conservation of Energy
• Energy is neither lost nor gained
• Motion
• speed, velocity, and acceleration.
• Forces
• Newtons three laws of motion

The eternal mystery of the world is its
comprehensibility. The fact that it is
comprehensible is a miracle.
Albert Einstein (1879 1955) Physicist
3
What are Matter and Energy?

• matter material such as rocks, water, air.
• energy what makes matter move!

• Three basic types of energy
• Kinetic energy of motion
• Potential stored energy
• Radiative energy transported by light
• Energy can change from one form to another.

4
Pre-lecture Question

• When energy is converted from one form to
  another, a tiny amount is inevitably lost
• A) True
• B) False

5
Pre-Lecture Question

• Which of the following statements correctly
  describes the law of conservation of energy?
• A) The total quantity of energy in the universe
  never changes
• B) An object always has the same amount of energy
• C) The total kinetic energy of the particles in
  any substance must always stay the same
• D) When an object appears to lose energy, that
  energy has not really disappeared, but instead
  has been transformed into heat

6
Kinetic Energy Macroscopic and Microscopic

• Kinetic energy of moving object
• Faster or more mass ? more KE (KE ½ mv2 )
• Heat / Thermal Energy
• Total KE of all particles within a substance
• Larger for more particles or more KE per particle
• Temperature
• Average KE per particle

7
Temperature Scales
8
Energy Question

• Bruce Moose (large) and Zeus Moose (small) are
  thrown with equal speed.
• A Bruces kinetic energy is smaller than Zeus
• B Bruces kinetic energy is larger than Zeus
• C Their kinetic energies are equal
• D Zeus knows you cant tell from the information
  given

9
Energy Question

• Minerva the Pig (large) and Violet the Skunk
  (small) are thrown with equal speed.
• A Minervas kinetic energy is smaller than
  Violets
• B Minervas kinetic energy is larger than
  Violets
• C Their kinetic energies are equal
• D Violet knows you cant tell from the
  information given

10
Potential Energy

• Stored Energy
• Batteries
• Springs
• Chemicals
• Objects in Gravity
• Building blocks of matter

11
Chemical Potential Energy

• chemical PE energy stored can be released
  through chemical reactions
• Chemical reaction in batteries
• Wood-burning
• Coal energy plants
• Rocket / Space Shuttle fuel

12
Gravitational Potential Energy

• gravitational PE energy stored because an object
  can fall
• Depends on
• objects mass (m)
• distance which it falls (d)
• strength of gravity (g)

g
m
d
13
Potential Energy Mass-energy

• energy stored in matter itself
• mass-energy

E mc2
c 3 x 105 km/s is the speed of light
14
More about Energy

• Radiative Energy carried by light
• Amount of Energy is always constant
• When a candle burns
• When a piece of toast falls
• When a bomb goes off
• When a train crashes

15
Conservation of Energy

• Energy cant be created or destroyed.
• This law is fundamental to science
• The total energy content of the Universe was
  determined in the Big Bang and remains the same
  today
• Experiments match predictions of this Law

16
Animation assumes no atmosphere
17
Post energy lecture Question

• When energy is converted from one form to
  another, a tiny amount is inevitably lost
• A) True
• B) False

18
Post-Energy Lecture Question

• Which of the following statements correctly
  describes the law of conservation of energy?
• A) The total quantity of energy in the universe
  never changes
• B) An object always has the same amount of energy
• C) The total kinetic energy of the particles in
  any substance must always stay the same
• D) When an object appears to lose energy, that
  energy has not really disappeared, but instead
  has been transformed into heat

19
Objects in Motion

• speed rate of motion
• distance traveled per unit time m/s mi/hr
• velocity speed in a certain direction
• e.g. 10 mi/h moving east
• acceleration a change in velocity
• i.e. change in either speed or direction m/s2

• mass the amount of matter in an object

20
Objects in Motion Question

• Which of the following does NOT describe an
  acceleration?

A) a car traveling with constant speed on a
straight road B) a car traveling with constant
speed around a bend C) a planet traveling in its
orbit around the Sun D) a car decreasing speed on
a straight road
21
Forces

• Forces change the motion of objects.
• momentum the (mass velocity) of an object
• force anything that changes an objects
  momentum
• Force changes velocity (if mass unchanged)
• i.e. changes direction or speed of motion!

acceleration
22
Conservation Laws

• Fundamental Laws of Nature
• Recall energy is conserved (doesnt change)
• Momentum conserved
• If no net (total) force
• Speed direction of motion unchanged
• Angular momentum
• momentum of spinning /circling
• Conserved if no net twisting force
• Spinning Figure Skaters are excellent examples of
  this

23
Newtons Laws of Motion 1
Newtons Laws aspects of Conservation of
Momentum

• 1) If no net (overall) force acts upon it, an
  object moves with constant velocity
• Velocity 0 if at rest

• If an object is left alone, its momentum doesnt
  change
• (Momentummass x velocity)

24
Newtons Laws of Motion 2

• 2) A net force accelerates an object in the
  direction of the force
• Same force accelerates massive object less
• More force ? more acceleration

F m a

• A force can change an objects momentum

25
Newtons Laws of Motion 3

• For any force, there is always an equal and
  opposite reaction force

• Total momentum is unchanged

26
Newtons Laws of Motion 3

• For any force, there is always an equal and
  opposite reaction force

• total momentum is unchanged
• If one objects momentum changes due to a force,
  then another equal and opposite force
  simultaneously changes some other objects
  momentum by a precisely opposite amount

27
Rocket Launches
Rocket launch
Pegasus rocket launch
28
ConcepTest
You are an astronaut taking a spacewalk to fix
your spacecraft with a hammer. Your lifeline
breaks and the jets on your back pack are out of
fuel. To return safely to your spacecraft
(without the help of someone else), you
should A) throw the hammer at the space ship to
get someone's attention. B) throw the hammer away
from the space ship. C) use a swimming motion
with your arms. D) kiss your ship good bye.
29
Gravity A special Force

• Falling objects accelerate due to Earths gravity
• Velocity at impact depends on height of drop

• Galileo acceleration g is the same for all
  objects

30
The Acceleration of Gravity (g)

• Galileo g is the same for all objects,
  regardless of their mass!

• Confirmed by Apollo astronauts on the Moon, where
  there is no air resistance.

31
Gravity Bridging physics on Earth to physics in
Space

• Falling objects accelerate due to Earths
  gravity.
• Velocity at impact depends on height of drop

• Objects in orbit are also accelerating due to
  gravity
• Example Moon orbits Earth

Newton
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Gravity Energy

• Falling objects convert GPE into KE
• If theres an impact, KE has to go somewhere!
• Sound
• Vibration
• Smashing objects into pieces
• Excavating craters
• Heating up