Physics Notes
Physics is the study of the interactions between energy, force and motion
Energy is the ability to move things

Our lives depend on moving things around. Think of all the things you move every day that help you meet
your needs. Our hearts pump blood, our muscles move our bodies, engines move cars, your heater moves
warm air through your house. Everything that uses electricity depends on moving electrons (including
phones, lights, computers, iPads, iPods, radio speakers, etc.)
 We classify energy in order to better understand it. This table summarizes the six forms of energy.
Form of Energy
Examples
Mechanical energy – Energy of moving things.
Moving water, moving air (wind), sound, any
movement of any object.
Heat energy – Energy of the movement of particles that
Every object has heat energy. Hot objects have
make up matter. The faster the particles are moving the
faster moving particles than cold objects, but
more heat energy they have.
cold objects still have heat energy.
Chemical energy – Energy stored in the chemical bonds
Food, batteries, anything you can burn such as
between atoms. We can use this energy when we break
fire, gas, coal, candles, alcohol
these bonds like when we burn something.
Electromagnetic energy (light) – Energy of moving light
Visible light, radio waves, infrared light, gamma
waves.
rays, ultraviolet light (UV light), and X-rays.
Nuclear energy – Energy stored in the nucleus of atoms.
We can use this energy when split a large nucleus (fission)
or when we combine two smaller nuclei (fusion).
Electrical energy – Energy of moving electrons. We make
electrons move through the use of moving magnets.

Fusion in the Sun, nuclear reactors, nuclear
bombs.
Phones, lights, computers, electric motors,
etc.
Energy can also be classified in a different way: as potential energy or kinetic energy.
o Potential energy is energy that is stored. It is not moving anything now but it has the potential to
move something.
 Chemical energy is potential energy because it is stored in chemical bonds. It doesn’t do
anything until the bonds are broken and the energy is released.
 Nuclear energy is potential energy because it is stored in the nucleus and isn’t released
until you fuse or split atoms.
 Mechanical potential energy comes from the shape of an object. For example, when a
rubber band is stretched is has mechanical potential energy because it has the potential to
move. Springs are another common object that has mechanical potential energy.
 Gravitation potential energy (GPE) comes from the position of an object. When an object
can move because of gravity it has GPE. Water in a dam is a good example of this. The
higher an object is, the more gravitational potential energy it has.
o Kinetic energy is energy that is actually moving something. Moving light waves, moving electricity,
and moving objects have kinetic energy. The faster the object is moving, the more kinetic energy it
has. The more mass the object has, the more kinetic energy it has.
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Physics Notes
One of the basic laws of physics is that energy cannot be created from nothing or be destroyed. It can change
forms though.
 Energy is constantly changing from one form to another.
o Potential energy – kinetic energy conversions are best understood by looking at a pendulum.
Remember that kinetic energy is highest where the object is moving fastest, and potential energy is
highest where the object is highest.
 At position #1 it is not moving so it is 100% potential energy. As it moves down to position
#3, it gains speed (and therefore kinetic energy). The potential energy converted into
kinetic energy. At position #3 it has its maximum speed so it is 100% kinetic energy. As it
moves back up to position #5, it converts back into potential energy.
 Potential – kinetic energy conversions are also important on rollercoaster. At the top of
hills, the rollercoaster has higher potential energy, and lower kinetic energy. As it goes
down the hill, potential energy decreases and kinetic energy increases until it reaches it
maximum speed.
o
Energy never disappears but it is not always in a usable form. Important energy conversions
happen to change energy into forms we can use for many of the tools we use in modern society.
 Watching a T.V. (energy comes from a coal burning power plant) – Coal (chemical energy) is
burned and converted into electricity. This electricity travels to the TV and is converted to
light and sound energy. Sunlight energy is converted to chemical energy in coal (coal is
made up of dead plants) through photosynthesis. Nuclear energy in the sun is converted to
light energy through nuclear fusion.
 Listening to a radio (energy comes from a dam) – Nuclear (sun)  Light (electromagnetic)
 GPE (water evaporating then falling as rain)  Mechanical (water flowing through the
dam) Electricity  sound (mechanical)
 A person exercising – Nuclear (sun)  Sunlight  Chemical (food)  Mechanical and heat
energy
Living organisms are constantly sensing the energy around them in order to help them survive.



Humans sense light energy with their eyes. Your eye takes light energy and converts it into electrical
impulses that travel to your brain through nerves and are interpreted. We use glasses or contacts to
change the light so we can focus it better. Telescopes, microscopes, and magnifying glasses change light to
make images appear bigger or smaller to our eyes.
We sense sound energy with our ears. Our ears collect sound energy (vibrating air molecules) and convert
it into electrical impulses that our brain interprets as sound. Hearing aids and cochlear implants are
examples of technologies that help us hear better.
Seismographs are a technology that we use to detect the vibrations (mechanical energy) in earthquakes.
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Physics Notes
Energy often moves as waves

Waves can be described by their wavelength, amplitude and frequency.
o
o
o
o

Wavelength is the distance from one crest to the next crest.
Amplitude is the height of the wave.
Frequency is the number of waves that pass a certain point per second.
Most waves need a medium to pass through (Light waves are the exception). A medium is the
substance it is passing through. When waves pass from one medium to another they change speed
depending on the density of the medium.
Light energy moves as a wave. The wavelength of the light determines the different types of light (gamma
rays, UV light, visible, infrared, radio waves) and the different colors of light (red, orange, yellow, green,
blue, indigo, violet). The shorter the wavelength, the higher the energy of the wave. Gamma rays are very
energetic and can damage living things. Radio waves have a low energy and don’t damage living things.
o
Light waves can pass through solids, liquids, gasses, and empty space. When light waves pass from
one substance to another they will change speed and bend. Waves of different wavelengths will
bend at different angles. This is why white light separates into a rainbow when it passes through a
prism (A raindrop acts as a prism in rainbows).
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Physics Notes

Sound waves travel as waves. Sound is always produced by something vibrating. These vibrations are then
transferred to air molecules. The air molecules will compress and then decompress. These compressions
are passed through the air. Sound can also travel through solids, liquids and gasses but cannot travel
through empty space.


Earthquake energy also travels as seismic waves through the Earth’s crust.
As energy spreads out from its source, it travels in all directions. Think of it as the layers of an onion
spreading out in all directions. As it spreads out, the energy gets less intense. This is why light is less
bright, sound is softer and Earthquakes are less damaging further away from their source.
Heat energy can travel in three different ways

Conduction – This happens when two objects touch. Heat energy will always travel from the hot object to
the colder object. Examples: Cooking something on a pan.

Convection – This happens when warm molecules are moved from one place to another. Examples: Warm
air or warm water rises because it is less dense, blowing warm air through your house, hot magma rises up
from the mantle to the Earth’s surface, forming volcanoes.

Radiation – This happens when heat travels as light waves. Examples: Humans give off infrared light (that’s
how night vision goggles work), the suns heat is radiated to Earth, light bulbs, fire.
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Physics Notes
In order for something to move there has to be a force pushing or pulling it

There are four fundamental forces in the Universe
o The strong force helps hold the nucleus of an atom together
o The weak force is involved in radioactive decay
o The electromagnetic force is a force that causes similar charges to repel
each other and opposite charges to attract each other. This force holds
atoms and molecules together. It also produces force every time two
objects touch each other. The electrons in the atoms repel each other
whenever two objects touch.

o
Friction is an important force we deal with daily. Sometimes we want to increase friction
and other times we want to decrease friction. Friction can be described in three ways:
 Sliding friction – friction between two solid objects. Examples: Tires and the
ground, brakes on your car or bike, shoes and the ground.
 Rolling friction – when one of the objects can roll. This reduces friction. Examples:
Wheels, ball bearings, gravel on a road.
 Fluid friction – when one of the objects is a solid or a liquid. This reduces friction.
Examples: oil in your car, air friction, friction with water.
 When do we engineer things to increase friction?
 Tire tread, shoe tread, brakes, bath tub, grip on gloves and handlebars
 When do we engineer things to decrease friction?
 Aerodynamics (planes, boats, fish), oil on moving parts, wheels
Gravity is the force of attraction between any two objects with mass.
 The force of gravity increases as the mass of the objects increase. The force of gravity
between two pencils is super small because their masses are so small. The force of gravity
between a pencil and Earth is big because the Earth’s mass is huge.
 The force of gravity on a car is bigger than on a bike because the car has a bigger
mass than the bike.
 The gravity on Jupiter is bigger than Earth because Jupiter has a large mass. On the
moon, the gravity is smaller because the moon has a small mass.


The force of gravity decreases as the two objects get further away from each other.
 The force of gravity is smaller on the top of Mount Everest than it is at sea level
(although the difference is really, really small).
Engineers have to plan for all of the forces on objects in order to get them to move the way they want
them to
o Buildings, bridges, chairs, tables, and cabinets are all engineered to support an object’s weight.
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Physics Notes
Mass and weight are different properties of matter

Mass is a measure of the amount of matter in an object.
o The mass of an object doesn’t change no matter where it is in the Universe.
o To measure mass, you compare the object to other objects of known mass. A balance scale is used
to do this.

Weight is a measure of the pull of gravity on an object.
o Weight changes depending on the mass of the planet it’s on and the distance from the planet.
o To measure weight, you use a compression scale or a spring scale. It measures how hard it is
pushing or pulling on the scale.
Simple machines are used to change how force is applied on an object

When using a simple machine, you apply a force on the machine called the effort force. The machine then
applies a force (the resistance force) on the object you are moving.
o
Simple machines make work easier by making the effort smaller. The trade off is you have to apply
the effort force for a longer distance. This produces a larger resistance force that is applied over a
shorter distance.
big distance = big resistance force

Small effort force x
x small distance
Mechanical advantage is a number that tells you how many times easier it is to move something using a
simple machine. For example, if you have a mechanical advantage of 5, then it is 5 times easier to lift the
object by using a simple machine. Your effort force would be 5 times smaller than the resistance force.
This also means that you would have to apply the effort force 5 times further.
o Example problem: You apply an effort force of 100 lbs. to a hammer. The hammer then applies a
resistance force of 1000 lbs. to a nail. The mechanical advantage would be 1000/100 = 10.
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Physics Notes

There are six simple machines.
o Lever – a rod that pivots around a fulcrum.
 To increase the mechanical advantage of a lever, you would move the effort force further
away from the fulcrum or move the resistance force closer to the fulcrum.
 Examples: hammer, catapult, pliers, scissors, door handles, wheel barrow
Lower mechanical advantage because the fulcrum is
Higher mechanical advantage because the fulcrum is
closer to the effort and further from the resistance
further from the effort and closer to the resistance
o
Inclined plane – a surface that slopes up.
 To increase the mechanical advantage of an inclined plane, you would make it less steep,
which would make it longer. Ramp A below has a higher mechanical advantage.
 Examples: Hiking path, roads, ramp, stairs
o
Wedge – an inclined plane that moves
 To increase the mechanical advantage of a wedge, you would make it sharper. Wedge b
below has the highest mechanical advantage.
 Examples: Knife, axe, hatchet, nails, staples (anything that is sharp)
o
Screw – an inclined plane wrapped around a cylinder
 To increase the mechanical advantage of a screw, you would make it less steep. This
means the threads would be closer together.
 Examples: Nuts, bolts, wood screws, drills, spiral staircase, car jack, clamps
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Physics Notes
o
Wheel and Axle – to cylinders attached to each other with one of them being smaller. The smaller
one would be the axle and the bigger one would be the wheel.
 To increase the mechanical advantage of a wheel and axle, you can make the axle smaller
or the wheel bigger.
 Examples: Screwdriver, door knob, steering wheel, gears, car and bike wheels
o
Pulley – A rope wrapped around a wheel
 To increase the mechanical advantage of a pulley, you add more pulleys
 Examples: block and tackle (sailboat), cranes, elevators, bike chain
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Physics Notes