Download Energy - the ability to cause change. Divided into 2 categories: 1

Energy - the ability to cause change. Divided into 2 categories:
1) potential energy - energy that is stored
2) kinetic energy - energy that is transferred and/or transformed
work  transfer of mechanical energy
heat  transfer of energy from colliding molecules (the faster they collide the higher the heat)
= energy transformations occur when energy changes from one form to another
chemical energy  your body converts or transforms the food you eat from potential energy (when
it was a pizza) to chemical energy (a type of kinetic energy) used by the body to move, grow, etc.
Law of Conservation of Mass and Energy = energy is never lost or gained – it only changes form – energy
is never created or destroyed only changed.
-- potential energy in wood is transformed into chemical energy => fire
different amounts of kinetic energy:
-- amount of kinetic energy an object has depends on the mass of the object and the speed of the object
=> more mass = more kinetic energy  think of the lab with the 4 different masses of balls. Ex. bowling
ball or baseball striking pins
=> more speed = more kinetic energy  think of the lab with the 4 different speeds of the marbles
Forms of Energy
5 main forms:
1) Mechanical energy – matter that is in motion. Ex. water in a waterfall or blood flowing through
the body
2) Heat energy – all matter is made of tiny particles – atoms – that are in constant movement. The
internal motion of atoms => heat energy. The faster particles move <-> the more heat energy is
produced.
 usually results from friction. Ex friction from rubbing hands together – mechanical energy is
converted into heat energy
 causes changes in temperature and phase of any form of matter. Ex. ice  liquid  gas
3) Chemical energy – the energy required to bond atoms together
-- when bonds are broken – chemical energy is released  an exothermic reaction
Ex: when you digest food – bonds are broken to release energy for the body to store and use
4) Electromagnetic energy – moving electric charges. Ex. power lines carry electromagnetic energy.
light – each color (red, orange, yellow, green, blue and violet) represents a different amount of
electromagnetic energy. x-rays, microwaves, radio waves carry EM energy
5) Nuclear energy – the nucleus of the atom is the source of nuclear energy
-- when the nucleus splits, nuclear energy is released in the form of heat and light energies
(nuclear fission  atomic bomb)
-- when the nucleus fuses together at high speeds with other nuclei (nuclear fusion  Sun).
Nuclear fusion of 4 hydrogen atoms fuse to form Helium
Energy Calculations: KE = (mass x velocity) / 2
GPE = weight x height
Work – when a force causes an object to move over a distance
-- amount of work done depends on the amount of force applied and the distance the object is moved
Work = force x distance
W = f*d
-- If the force doesn't produce motion, no work is done
Machines & Work
machine – a device that transfers mechanical energy from one object to another object
-- they make work easier to perform
-- they multiply force and change the direction or the distance over which a force is applied
Ex: wrench – multiplies force
pulley – changes direction of a force
loading ramp – increases the distance but reduces the force
The force a machine has to overcome – resistance
The force applied – effort
(Using a machine reduces the amount of effort needed to overcome a given amount of resistance)
Ex: lever
Simple machines
6 simple machines: lever, pulley, wheel & axle, inclined plane, wedge and screw
Efficiency of Machines
* Machines are never 100% efficient *
-- the amount of work done by a machine is always less than the amount of work put into it
-- some work is wasted. some is converted to heat energy produced by friction
% efficiency machine = (work output / work input) x 100
Power – rate of doing work
-- Doing work at a faster rate requires more power. To increase power, you can increase the amount of
work done in a given time.
Power = (Force x distance) / time
or
Power = Work / time P = w/t
Unit of power – watt
P = (f*d) / t