Transcript Friday PS 11-2 - elyceum-beta

Friday PS 11-2
Answers to homework
Hand in homework
• Mousetrap game chart
• Halloween questions
• (Simple machine pictures)
Mousetrap questions?
Answers to Page 390 HW
1) lever, pulley, wheel and axle, inclined plane,
wedge, and screw
2) a. screw b. inclined plane
c. 1st class lever
3) Bigger output force exerted over a smaller
distance
4) Middle of pulley is fulcrum, outside edge of
wheel is like a lever extended into fulcrum.
They are different because you can change
the position of the fulcrum of a lever
HW p390
5) A long, thin wedge has a greater
mechanical advantage than a short, wide
wedge because of ratio of its length to its
height is greater
6) No
7) Greater distance input uses less input
force
8) Answer will varying
Energy
• Is the capacity to do work
• Work is the quantity of energy transferred
by force to an object that results in
movement of object in direction of force
• Energy is the currency of physics
Energy units
• Since the amount of work done = the
amount of energy transferred…
• Wherever work is done, energy is
transferred or transformed to another
system
• The units for work and energy are the
same
Energy is like money
• Different types of money- different forms of
energy
• Supplies the ability to produce a certain
type of force or means to store the energy
for later use
– Action
– Storage
Mechanical energy
• The amount of energy available for use or
storage by macroscopic physical means
• Energy related to what you can do with or
to an object
Mechanical -vs- nonmechanical
energy
• Non-mechanical Energy
• Energy that lies at the level of atoms and
that does not affect the motion on a large
scale
– Thermal energy
– Chemical energy
– Nuclear Energy
– Electrical Energy
Potential energy
• Stored energy
• 2 forms of mechanical potential energy
– Elastic Potential Energy (EPE)
• Store by changing shape
– Gravitational Potential Energy (GPE)
• Store by changing location
• Can calculate GPE as
– GPE = mgh
• g = acceleration due to gravity (9.8 on Earth)
• h = distance above the reference line
Elastic potential energy
Kinetic Energy
•
•
•
•
Energy of motion
KE = ½mv2
m = mass
v = velocity
Problems on energy
• Class Examples:
In Class Assignment
• Energy Problem Handout
• Watch for units