kernersville middle school

KAREN STOREY

Kernersville Middle School

7TH GRADE SCIENCE

March 9,2016

ENERGY: CONSERVATION & TRANSFER

COMMON CORE ESSENTIAL STANDARD: 7.P.2.2

• Objects that have potential energy do not use their energy until they move.

•Potential energy means that the energy is stored. For example: Oil in the ground is potential energy.

• Potential means that something is capable of becoming active.


• Energy of motion is called kinetic energy.

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Kinetic energy appears as light, heat, sound, or electricity.

• Energy is always recycling itself, from potential to

kinetic. For example: Burning fossil fuels heats our home, keeps us warm, and allows us to cook our food.


• Energy is one of the fundamental building blocks of our universe.

• Energy can change from one form to another, although in the process some energy is always converted to heat (thermal energy).

• Some systems transform energy with less loss of heat than others.

ESSENTIAL STANDARDS GOAL 7.P.2.3

Energy can be transferred from one system to another (or from a system to its environment) in different ways such as:

1. Thermally, when a warmer object comes in contact with a cooler object.

2. Mechanically, when 2 objects push or pull each other over a distance.

ESSENTIAL STANDARDS GOAL 7.P.2.3

3. Electrically, when an electrical source, such as

a battery or generator is connected in a complete

circuit or electrical device.

4. Electromagnetic waves a radio wave, a wave

of visible light, or an X-ray) that consists of an

associated electric and magnetic effect and

travels at the speed of light. (3.00 x 10 ‾⁸ m/s²)


Anytime energy transfers, or changes form, some of the

energy is always converted to heat energy. AKA: Thermal

energy

Energy sources are either nonrenewable (such as fossil

fuels), or renewable (such as solar (sunlight), wind, or

water (hydro))

• Renewable energy – AKA: Green energy: DOES NOT

POLLUTE THE ENVIRONMENT.

ELECTRICAL ENERGY

•The electrical energy generated by windmills, waterfalls and power plants is actually a secondary source of energy.

• To produce electricity, a heat source is needed to create the conditions in which electrical currents form.

•The primary source of electrical energy is the heat generated by burning fossil fuels, water power and/or wind power.

A natural form of electrical energy can be seen in the lightning that appears during storms.

ELECTRICAL ENERGY

• Electrical energy can be produced from a variety of energy sources and can be transformed into almost any other form of energy.

•Electricity is important because we can use it to make so many things work. Electrical circuits require a complete loop through which an electrical current can pass.

•For example: a bulb converts electrical energy into light energy, thermal energy and a speaker converts it into sound energy. Remember: Electrical circuits require a complete loop to pass electrical currents.

•


Mechanical energy: the energy possessed by an object due to its motion or its stored energy of position.

Mechanical energy can be either kinetic (energy of motion) or potential (energy of position).

MECHANICAL ENERGY

• An object that possesses mechanical

energy is able to do work.

• Mechanical energy is the form

involved in the operation of simple

machines.


• A machine is a device that makes work easier by changing the size or direction of a force.

• When you use a machine, you do the work on the machine, and the machine does the work on something else.

• Remember: A simple machine only has 1 movement.


• Mechanical advantage is the number of times the machine multiplies force.

•Ideal Mechanical Advantage (IMA) is what is desired of a machine, where Actual Mechanical Advantage (AMA) is what the machine actually does.

MECHANICAL ADVANTAGE

• Actual Mechanical Advantage = Ratio

of load to effort. AMA = Load or

Output/Effort or Input

• To calculate the AMA Ratio for gears:

# of output teeth/ # of input teeth

MECHANICAL EFFICIENCY

To calculate a machines efficiency is almost the same as

calculating a machine’s advantage. You use the same formula

and then multiply your answer by 100 to show %.

Output/Input = Answer x 100 = Efficiency

Solve this problem:

If a machine takes in 65 J (Joules) and puts out 52 J of

energy what is its efficency?

THE 6 TYPES OF SIMPLES MACHINES 1. Inclined plane - A simple machine that is a straight, slanted surface, and facilitates the raising of loads .

2. Wedge – thick at one end and tapers to a thin edge at the other end.

3. Screw – an inclined plan wrapped around a central cylinder to form a spiral.

THE 6 TYPES OF SIMPLES MACHINES

4. Lever - a simple machine that has a bar that pivots at a

fixed point called a fulcrum

5. Wheels & Axle - A simple machine that consists of two

circular objects of different sizes

NOTE: The mechanical advantage of a wheel and

axle is the radius of the wheel divided by the radius of

the axle.

6. Pulley - a simple machine that consists of

a wheel over which a rope, chain, or wire

passes.

INCLINED PLANE

•Simplest of ALL simple machines because to make it work, nothing moves. You move!

•Another name for an inclined plane is a ramp. A ramp works by helping you lift things more easily up to a higher level.

•The Mechanical Advantage (MA) of inclined plane is found by dividing its length by height.

INCLINED PLANE

•Remember, there's always a trade-off.

The way an inclined plane works is that to save effort, you must move things a greater distance.

•The ancient Egyptians figured this out over 3,000 years ago when they built their pyramids. They used long, shallow ramps to help them move the heavy stones to the top!

WEDGE

• A wedge is really an inclined plane turned on its side.

•A wedge helps you push things apart. The blades of a knife or a shovel are both wedges. A wedge can also be round, like the tip of a nail, or the tines on your fork. Basically, the wedge works just like a ramp: The narrower the wedge (or the sharper the point of a wedge), the easier it is drive it in and push things apart.

•Here's the trade-off: To split something apart really wide, you have to push the wedge a long distance.

SCREW

• The screw is really an inclined plane in the round with a wedge at the tip.

•Think of a typical screw. The wedge is the pointed end. The inclined plane is the thread that wraps around the screw.

•Screws are used in many different places to hold things together.

SCREW

Basically, a screw is like the ramp — and the width

of the thread is like the angle of an inclined plane.

The wider the thread of a screw, the harder it is to

turn it.

Here's the trade-off: If you've ever had to put in a

screw with really narrow threads, you've probably

found that you have to turn it a really long time to get

it to go anywhere. Just like in a ramp, the easier the

effort, the longer the distance you have to move

something! .

LEVER

A stick that is free to pivot or move back and forth at a certain point. Levers are probably the most common simple machine because just about anything that has a handle on it has a lever attached.

The point on which the lever moves is called the fulcrum. By changing the position of the fulcrum, you can gain extra power with less effort.

LEVER

A good example of a lever is a see-saw. Let's say

that you're really light, and you want to lift a really

heavy person on the opposite side. If you put the

fulcrum in the middle, you won't have a chance. But if

you slide the fulcrum closer to the heavy person, it will

be easier to lift.

Where's the trade-off? Well, to get this helping hand,

your side of the see-saw is much longer (and higher

off the ground), so you have to move it a much greater

distance to get the lift.

WHEEL AND AXLE •A wheel and axle is really two machines in one because you can use each part in different ways.

•Wheels help you move an object across the ground . They reduce the amount of friction between what you're trying to move and the surface you're pulling it against.

•The axle is the object that attaches the wheel to the object it's moving. Since only the very bottom of the wheel touches the ground, there is less surface area to rub — and less friction.

WHEEL AND AXLE

NOTE: The mechanical advantage of a wheel

and axle is the radius of the wheel divided by

the radius of the axle.

•The trade-off: The larger the diameter of the

wheel, the less effort you need to turn it, but you

have to move the wheel a greater distance to

get the same work done. Generally speaking,

the bigger the wheel, the easier it is to make

something roll.

THE PULLEY

• The pulley is really a wheel and axle with a rope or

chain attached.

• A pulley makes work seem easier because it

changes the direction of motion to work with

gravity.

THE PULLEY

A pulley really saves effort when you have more than

one pulley working together. By looping a rope

around two, three, or even four pulleys, you can

really cut down on the effort needed to lift

something.

The trade-off: As you increase the number of

pulleys, you also increase the distance you have to

pull the rope. In other words, if you use two pulleys, it

takes half the effort to lift something, but you have to

pull the rope twice as far.

COMPOUND MACHINE

• A compound machine consists of two

or more simple machines put together.

• In fact, most machines are compound

machines.

• Examples of compound machines:

a pair of scissors or a bicycle.

IMPORTANT SCIENCE LAW

LAW OF CONSERVATION OF ENERGY:

ENERGY CANNOT BE CREATED NOR DESTROYED,

BUT IT CAN CHANGE FORM.

FACT: Everything we think we have thrown away is

still here with us in one form or another.

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