Energy

 Work is done when a force acts on an object and the object moves in the direction of the force  W = Fd (measured in joules)  Two types of force  Work against another force (friction)  Work done to change the speed of an object

 Power equals the amount of work done divided by the time interval during which the work is done  P = W/ t  Power is measured in watts (W)

 Like work, energy is measured in Joules  The two forms of mechanical energy are kinetic and potential energy

 Three examples of potential energy:  1) Elastic Potential Energy- A stretched of compressed spring  2) Chemical Energy- Chemical energy in fuels  3) Gravitational Potential Energy- potential energy due to elevated positions ▪ PE = mgh (mass X gravitational constant X height)

 KE = ½ mv^2 (½ mass x speed^2)  The kinetic energy of a moving object is equal to the work required to bring it to its speed from rest, or the work the object can do while being brought to rest  Fd = 1/2 mv^2

 States that whenever work is done, energy changes  Work = delta (“change in”)KE  If there is no change in an objects KE, then we know no net work was done on it.  The more KE something has, the more work is required to stop it.  Figure 9.5 page 152

 States that energy cannot be created or destroyed. It can be transformed from one form into another, but the total amount of energy never changes.  Figure 9.9 page 154

 A machine transfers energy from one place to another or transforms it from one form to another  Lever- made of a bar that turns about a fixed point. We do work on one end and the other does work on the load.  Work input (F x d) = Work output (F x d)  Mechanical advantage = Output/ Input  Figure 9.12 page 156

 Pulleys are a kind of lever that can be used to change the direction of a force.  Mechanical advantage for a pulley is the same as the number of strands of rope that actually support the load.  1 strand = MA of 1  2 strands= MA of 2 Figure 9.13 page 157

 In any machine, some energy is transformed into atomic or molecular kinetic energy- making the machine warmer.  Efficiency = useful work output/ total work input  Inclined Planes- a machine (pushing farther means lifting with less force)  Efficiency = actual MA/ theoretical MA

 There is more energy stored in the molecules of food than there is in the reaction products after the food is metabolized. This energy difference sustains life.

 The sun is the source of practically all our energy on Earth  Solar Power- Sunlight directly transformed into electricity by photovoltaic cells  Fuel Cells- hydrogen and oxygen combine to produce water and electricity  Nuclear Energy is stored in uranium and plutonium  Geothermal Energy is stored in underground reservoirs