Chapter 7: Understanding Energy Transfer Technologies

What is Energy? Definition: Energy is the ability to do work.

There are a lot of different types of energy; potential energy, kinetic energy, thermal energy, electrical energy, light energy, sound energy, chemical energy and nuclear energy.

Examples: A baseball has kinetic energy because of it’s motion. An outlet is a source of electrical energy A light bulb gives off light energy

7.1 All Kinds of Energy

The energy possessed by a body by virtue of its position relative to others, stresses within itself, electric charge, and other factors.

Potential Energy

The energy which it possesses due to its motion. It is defined as the work needed to accelerate a body of a given mass from rest to its stated velocity.

Kinetic Energy

Energy stored in fuel which is released when chemicals react.

Chemical Energy

Energy stored in an object that is being stretched , squashed, twisted, etc.

Elastic Potential Energy

Energy stored in an atom’s nucleus.

Nuclear Energy

Energy transferred by an electric current.

Electrical Energy

Energy transferred through waves and light particles.

Light Energy

Energy transferred through sound waves

Sound Energy

Energy of an object due to its temperature. This is partly because of the random kinetic energy of the particles of the object.

Thermal Energy

The meaning of words can be changed depending on where you use them. For example, “work” is the place someone may go to make money. Similarly, you do house “work” or home “work” when you help around the house or study school subjects at home. These are the everyday meanings of “work”.

In physics, work is used in a difference sense.

Work is done only when an object is moved by applying a force to it. when you throw a baseball, you do work on the ball When you pull a toboggan, you do work on the sled

Work is done when a force moves an object.

What is work?

For example, it takes work to lift a heavy barbell, but it does not take work to hold the barbell over your head.

In either case, you would say you were working hard. But, for work to be done, the object must move.

Effort does not always equal work

Finding the amount of work

It takes about 100N of force to push a lawn mover forward. How much work would it take if you walked 1000m?

Steps in Solving in the Problem:

Step 1: Write out the formula. W = F x dStep 2: Substitute the numbers. W=100N x 1000mStep 3: Do the calculation. W = 100 000 Nm

or 100 000 JStep 4: Summarize the answer.

100 000 joules of work would be done.

Sample Problem

Step 4

Practice Problems

Practice Problems

Practice Problems

Definition: A machine that has only one movement

The oldest simple machine is a ramp (inclined plane)

What is a simple machine?

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Practice Questions

Levers: bars that pivot on a fulcrum

Lever Parts◦ Fulcrum: the supporting point◦ Load: the object being moved by the lever◦ Effort: the force required to move an object◦ Load distance: distance from the fulcrum to the load◦ Effort distance: distance from the fulcrum to the effort

7.2 Just Prying Into Things

In first class levers, the fulcrum is between the load and the effort.

First class levers are used for lifting, prying, and cutting. ◦ Example: a pair of scissors, the fulcrum is the

screw that holds the scissor blades together◦ Example: a pair of plyers

First Class Levers

In second class levers, the fulcrum is at one end and the effort at the other end with the load in the middle.

◦ Example: wheelbarrows and nutcrackers

Second Class Levers

In third class levers, the fulcrum is at one end and the effort is between the load and the fulcrum.

◦ Examples include: axes, rackets, and hockey sticks.

Third Class Levers

Your body has levers too!

First class: the triceps are the muscles that reach from the back of your upper arm and around your elbow.

Third class: the biceps the large muscle at the front of your upper arm, provides effort.

Levers in the Body

A distance multiplier moves a load through a large distance but requires a short effort distance.

A fishing rod is an example of a distance multiplier. In this machine a small movement by the effort (when you make a cast) produces a much larger movement of the load (fishing line moves meters away).

Distance Multipliers

A force multiplier is a simple machine that easily moves a large load.

A small force on the effort end of the lever puts a large force on the load.

Force Multipliers

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Practice Questions

A pulley is a simple machine consisting of a grooved wheel on which a rope or cable turns.

7.3 Wheels, Pulleys, and Blocks

Fixed Pulley A pulley that does not move and does not

change the effort required.

Movable Pulleys A pulley that moves with the load and

reduces the effort required.

Wheels and Axels A simple machine that consists of a wheel

turning a smaller rod Every time you turn a doorknob, you

operate a wheel and axel machine.

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Practice Questions

When your car is stuck in a snow drift, usually it does not help to spin your tires.

It wastes energy (not efficient), and often gets you stuck even worse.

When a machine is used, the machine will lose energy through:◦ Friction between moving parts◦ Heat given off by the cooling system or exhaust◦ Poor combustion of fuel

7.4 Spinning Our Wheels: Energy and Efficiency

A machine’s efficiency is a comparison of the work the machine does with the energy it uses to do that work.

No machine is 100% efficient. Meaning, the work output does not equal the work input.

Most of the energy used in Canada comes from burning fossil fuels, which lead to environmental concerns:◦ Burning fossil fuels contributes to global climate

change and air pollution◦ Fossil fuels are non-renewable

Efficiency

One way to deal with concerns related to burning fossil fuels is to reduce the amount of energy you use, either by using machines less or by changing to more efficient machinery.◦ Use energy efficient appliances

Dealing with Environmental Concerns

Use energy from renewable sources. o Windmills and solar panels provide

energy from renewable sources

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Practice Questions

Complete/Hand-in Assignment #7

Complete/Hand-in Simple Machines Research Project

Study for Unit B Test