NCFE Review Std 3 Energy

Energy

• The ability to do work or cause change

• Mechanical energy (something’s moving) – the sum of the energy within a system.

Made up of Kinetic, plus Potential, plus Dissipated, etc.

Momentum

• A property of all moving objects. • Calculated this way:

•

Momentum = mass x velocity

•

mass in kg, velocity in m/s

•

momentum unit is kg(m/s)

Also - momentum is conserved.

• Law of Conservation of Momentum: The total amount of momentum in a closed system is conserved.

Kinetic Energy

• The energy of motion

• KE = ½(mass)(velocity)2 _{remember – solve this thing from right to left.}

Potential Energy

• The energy of POSITION

Law of Conservation of Energy

• In a closed system, the total amount of energy is neither created nor destroyed, but rather, changed from one form to another.

Work

• Work is how energy is transferred

• Work = Force x distance (in meters) Unit = Joule

• Must have a distance, and the force and distance must be in the same direction

Power

• Power = work/time

• Do more work in a period of time, you’re increasing the power. Less work over the same time, you’ve got less power.

Simple Machines.

• They help with work…they don’t do it for you. (Those are robots)

• Simple machines change the size of an “input force” (the force you exert) or the direction of that force, or both.

• The point of simple machines is to be able to use less

Simple Machines – 6 Types:

• Levers

•

Class 1

•

Class 2

•

Class 3

• Pulleys

• Wheel and Axel

• Inclined Plane

• Wedge

Why is the work easier?

Simple machines give you a

mechanical advantage. It’s the

Inclined Plane Mechanical Advantage?

•

IDEAL Mechanical Advantage

= length

of incline/height of incline

•

Example: a 6 meter long plane that lifts

something 3 meters.

IMA = 6/3 = 2.

But…

• No machine is 100% efficient. The Actual Mechanical Advantage is LESS than the Ideal.

• Efficiency = [Work (out)/Work(in)] x 100%

Mechanical Advantage

•

Levers, pulleys and ramps:

•

Lever – IDEAL MECHANICAL ADVANTAGE –

length of effort divided by length of

resistance arm

•

Pulley – M.A. – the number of ropes

suporting the pulleys.

Heat & Temperature.

Temperature – a measurement of how hot or cold an object is. Measured with a thermometer

Heat something up – what happens?

Particles move faster.

Movement – what kind of energy is that?

The higher the heat, the faster the particles in

the substance are moving.

Heat is measured…

Heat

Changes

Things.

• What happens when you heat things?

Ice

Water

Heat transfer

• Conduction – direct contact

• Convection – in liquids and gasses, convection currents

• Radiation – how the sun heats the earth. Waves of energy

Heat Transfer

• Conductors – allow heat to move through them

• Insulators – slow or stop heat from moving.

energy

temp

era

ture

MATTER

SOLID

LIQUID

GAS

BOILING throughout

Exothermic – take away heat

FREEZING

Particles move slightly bumping against each other

Particles move by sliding past each other

Particles move quickly past each other

Density is:

•

The ratio between the mass of an object and its

volume (another way of saying how much “stuff”

there is in a given volume)

Density

2 Different Types of Mechanical Waves:

1. Transverse Wave

• Disturbance runs perpendicular to the wave’s direction

• Looks like a wave at the beach. • Can travel through vacuums

Transverse Wave Anatomy

Resting Point Nodes

Trough

Crest

Wavelength λ

2 Different Types of Waves:

2. Longitudinal Waves

• A.K.A. Compressional Waves

• Different names, same wave

• Disturbance runs parallel to the wave’s direction • Looks more like a Slinky

Sound Wave - Longitudinal

Compression

Rarefaction Amplitude

To repeat - longitudinal waves

• MUST have a medium in which to travel.

Transverse waves – DO NOT

need a medium in which to

Sound

Cool sound stuff…

• Supersonic (faster than the speed of sound)

• Subsonic (slower than the speed of sound)

• Sonic boom (what happens when you pass the speed of sound)

SURFACE WAVES

• Combine the properties of longitudinal and transverse waves.

• They happen at the surface between two mediums (surface of the water, the ground, etc)

• Particles in a surface wave travel in a circular path.

Frequency vs. Period

• Frequency is the number of waves that pass a point in a given amount of time.

• Measured in Hertz (Hz)

time

Speed of Waves

Wave speed is equal to the frequency of the wave times the wavelength.

• V

=

f



λ (units: meters/second, or equivalent)

When Waves Hit Things

Reflection:

Refraction

Refraction:

The wave enters a new medium and changes speed

• Examples – seen in a

prism or rainbow or the “magnification” of

Diffraction

The bigger the wavelength,

the smaller the frequency.

UNIVERSAL

SPEED

LIMIT

3.0 x 10

8

meters/second

•_{Colors line up: Red, Orange, Yellow, Green, Blue, Indigo (*),}

Violet, or: ROY G BIV

• * - some charts skip Indigo

•Remember – all colors are present in white light.

We see the color(s) that is/are reflected. All other colors are absorbed.

• _{Color depends on the WAVELENGTH and FREQUENCY}

Waves Behaving Badly

• Reflection

• SONAR, RADAR, mirror, echo, reflectors

• Refraction

• Prism, rainbows, diamonds, magnification, prisms

• Diffraction

SONAR

RADAR

Interference

Interference

• Constructive: the waves’ crests overlap, creating a wave with a bigger crest than the components.

• Destructive: The crest of one wave meets the

trough of another, and the resulting wave is less than its parts.

Interference

Colors from Interference

Oil or

soap

Interference examples:

•

Quiet spots in the auditorium where the sound is

“bad.”

•

An echo sounding louder than your original

voice.

•

Noise cancelling headphones.

Standing Wave

Two types of electricity

• Static – build up of charge

Schematics

Schematics

Electrical Circuits:

• Three things needed for a circuit:

• Source of electrons

• Path for the electrons to travel on

• Something to use the electrons

Open Circuit – the path is interrupted or “open”

Two Types of Circuits

• Series – only one path for the electrons to travel on (battery to a lightbulb – one light goes out, they all go out)

Three ways to put a charge on an object:

• Friction – charges rubbed off of one thing onto another

• Induction – balloon near the wall. Change in charge is induced

Ohm’s Law:

• V = IR where V=volts, I=current, and R=resistance

V

I

R

V = Voltage (volts)

I = Current (amps)

Resistance

•

The thinner the wire = higher resistance,

thicker the wire = lower resistance.

•

The longer the wire = higher resistance,

the shorter the wire = lower resistance.

Power!

• The rate at which electrical energy is supplied

• P=VI

• P – measured in Watts

• V – voltage

P

V

I

V = Voltage (volts)

I = Current (amps)

MAGNETS!

• All magnets always have two poles (north and south)

• Opposite poles attract

• Attract nickel, cobalt and iron

• Electromagnet – more turns of wire = stronger, more current = stronger.

•

Motor

– turns electrical into

mechanical energy

•

Generator

– turns mechanical into