Download CH 4 Energy

CH 4 Energy
I. Energy and Types
A. Energy – ability to do work or cause change
B. 5 general types of energy
1. mechanical – any movement
2. electromagnetic – light, radio waves, etc. (CH 13)
3. chemical – potential energy stored in chem.. bonds ex) food,
gasoline
4. thermal – heat
5. nuclear – stars + nuclear reactions
C. Types of mechanical energy
1. Kinetic Energy (KE) – energy of moving objects
a. formula: KE = ½ m x v2 ( m = mass, v = speed)
b. units – Joules (J)
ex) Find the KE of a 100 kg person running at 4 m/s.
KE = ½ x 100 x 42
KE = ½ x 100 x 16 = 800 J
2. Gravitational Potential Energy (GPE) – energy stored due to
position
a. formula: GPE = m x g x h ( h = height)
b. units: joules
ex) Find the gravitational potential energy of a 10 kg rock that
is 5 meters above the ground on a cliff.
GPE = 10 x 9.8 x 5 = 490 J
c. higher object more PE
3. Elastic Potential Energy (EPE) – energy stored in a stretchy object
ex) spring and rubber band
a. formula: EPE = ½ kx2
1) k – spring constant tells how much force is made for
each unit of distance of stretch or compression
2) x – how far spring is stretched or compressed from
normal length
II. Conservation of Energy
A. Law of conservation of energy - energy can neither be created nor
destroyed, but can change forms
ex) digested food turns chemical energy into body heat and movement
1. if bouncing ball did not convert KE to sound and heat, it would
bounce forever at same height
B. Falling Objects – GPE turns to KE as falling object moves faster
1. projectile - thrown object loses KE when rising, then regains as
falls
a. if lands at same height as thrown, will have same KE upon
landing as when first thrown
b. diagram
1) position A and E, KE max, GPE = zero
2) position B: KE decreasing, GPE increasing
3) position C: KE min., GPE max
4) position D: KE increasing, GPE decreasing
C. Pendulum – pg 110 – swinging objects (diagram side)
1. position A, E: max GPE, zero KE
2. position B: inc. KE, dec. GPE
3. Position C: Max KE, zero GPE
4. position D: inc. GPE, dec. KE
D. Mass/Energy Conversions – Einstein – mass traveling at speed of light
changes into energy
1. Formula E = m x c2 (E = energy, c = speed of light)
2. Conversion methods:
a. Fission – splitting atoms – nuclear power plants and bombs
1) starting atom split into 2 nearly equal sized atoms,
but some mass turns into energy
b. Fusion – small atoms combining to make bigger ones – sun
and bombs
1) in sun, 2 hydrogens form one helium and some mass
turns to energy
2) biggest atoms most stars can make is oxygen
3) bigger atoms formed in supernovas or big bang