Download Reveiw PPT 4_Energy_Power_Electrostatics_Circuits

Energy and Power
COMBINE
Energy – Conservation – Power
Into 1 summary sheet!
Energy is the ability to CHANGE an object.
These types of energy are a result of a
CHANGE in…….
Work:
Kinetic Energy:
Potential Energy:
Elastic Energy:
FORCE
VELOCITY
HEIGHT
SHAPE
Conservation of Energy
• In a system, the TOTAL
MECHANICAL ENERGY never changes
• Energy can switch forms, but it
cannot be created or destroyed.
WORK
KINETIC
POTENTIAL
ELASTIC
Examples
No matter type of energy transfer, the set up is the
same. Even if there is more than one type of energy
present
TME Initial
KE + PE + EE + W
=
=
TME Final
KE + PE + EE + W
Energy: Joules (J)
Work:
Kinetic Energy:
Potential Energy:
Elastic Energy:
W = Fd
2
KE = ½mv
PE = mgh
2
EE = ½kx
Examples
• A ball is dropped from a height of 12m, what is
the velocity of the ball when it hits the ground?
Potential Energy  Kinetic Energy
Since all of the energy is transferred, we can set them
equal to each other
PE = KE
m(9.8)(12) = ½(m)v2
15.33 m/s = v
 mass cancels
Examples
• A force of 50N pushes horizontally on a 5kg object
for a distance of 2m. What is the final velocity of
the object?
Work  Kinetic Energy
Since all of the energy is transferred, we can set them
equal to each other
Work = KE
(50)(2) = ½(5)v2
6.32 m/s = v
Sample Problem
• A 5kg cart moving at 2 m/s collides with a spring
that has a spring constant of k=5N/m. If all of the
cars kinetic energy is transferred into elastic
energy, what distance will the spring be
compressed?
Answer: 2m
POWER
Power = Energy/ time
P = E/t
On your equation sheet it lists “Energy” as Work
for the top of the fraction. But you can put
any type of energy on the top part of this
equation.
Sample Problem
• A 50kg man runs up a 5 meter tall stair case in
10 seconds. How much power does her exert in
climbing the stairs?
Answer: 245 Watts
Charge Basics and
Electrostatic Force
COMBINE
Charge Basics – Electrostatic Force
Into 1 summary sheet!
Electrostatics:
• Atoms have protons, neutron, and
electrons.
• Only electrons can move!
Charge of 1 electron = 1.6E-19 Coulomb (C)
Electrostatics:
• An object becomes charged when its
electrons are shifted or transferred
• Extra electrons = (-)
• Fewer electrons = (+)
Sample Problem 1:
• An object has a charge of -1.76E-18 C
charge. How did the object become
charged (gain or lose e-) and how many
unbalanced electrons does it have?
Answer: Gained 11 electrons
(Show work and explain why)
Electrostatics:
• Two charged objects will feel an
Electric Force
• Opposite charges attract (+/-)
• Same charges repel (+/+) (-/-)
Electrostatics:
• Calculating the Electric Force
q1q2
Fe  k 2
r
• k = 9E9
• q=charge
• r= distance between the charges
Sample Problem - 2
• Calculating the Electric Force
• k = 9E9

q1q2
Fe  k 2
r
What is the magnitude of the electrostatic
force between two electrons separated
by a distance of 1.00 × 10–8 meter?
Answer: 2.304 x 10-12 N
Circuits
Circuits:
• A circuit provides a COMPLETE path for
electrons to move.
• The flow of electrons is called the current (I).
• Electrons flow because a voltage (V) provides
an energy difference
• In order to get energy out of a circuit, there
has to be resistors (R).
V  IR
Circuits:
V  IR
Circuits:
Analyze Circuits using an RIVP Table
R
I
Units Ohms
R
V
P
Amps Volts Watts
I Very Powerful”
“ espect s
Circuits:
Series Circuits
• A circuit in which there is only one current
path
Circuits:
Series Circuit
• Current is the same in all resistors
I = I1 = I2 = I3 = I4
• Voltage is distributed among the resistors
V = V1 + V2 + V3
• Total Resistance is the sum of all resistors.
RT= R1 + R2 + R3
Sample Problem - 1 - Series
RIVP TABLE!
• What is the voltage in the 10 ohm resistor?
Circuits:
Parallel Circuits
 A circuit in which there are several
current paths
Circuits:
Parallel Circuit
• Current is the added in all resistors
IT = I1 + I2 + I3
• Voltage is equal among the resistors
VT = V1 = V2 = V3
• Total Resistance is the reciprocal of all resistors.3
1/RT = 1/R1 + 1/R2 + 1/R3
Sample Problem - 2 - Parallel
RIVP TABLE!