# Science Concepts Found in this Book

Few explanations of science concepts are given in the text as you will probably go through the book in a different order than it is presented here. When you read words in the text, it is assumed that you know the concept. If you don’t, or if you need a refresher, come to this section and review the science concept.

The purpose of this book is not to replace existing physics and chemistry books. For more detailed explanations, any simple high school text will make things clearer and give good examples.

## Newton’s Three Laws

Isaac Newton identified three physical laws that have been influencing man, the earth, and the universe from the beginning of time. They are simple.

### Inertia

The law of inertia says that an object continues in its state of rest or continues in uniform motion in a straight line until it is acted upon by an outside force. Something at rest will tend to stay at rest. Something in motion will tend to stay in motion.

Put a 3 x 5 card over the top of a glass or cup. Put a penny in the center of the card. Snap the card with your finger. What happens to the penny? This demonstrates inertia of an object at rest.

Travel in a boat, four wheeler, or snowmachine at a constant speed. Throttle down or put on the brakes. Why does your body go forward when the machine slows down? This demonstrates that a object in motion (your body) will stay in motion until acted upon by an outside force.

Centrifugal force

You notice that the law of inertia says that an object continues in uniform motion in a straight line. When an object is spun around, like a model airplane on a string, it has a tendency to go in a straight line, pulling against the string. The force of an object to fly away from the center when spun in a circle is called centrifugal force. Centrifugal means “fly away from center.”

### F = MA

The second law that Newton described was F = MA.

Force = Mass x Acceleration.

If an object is accelerated or decelerated, the force causing that change can be measured by multiplying the mass times the rate of acceleration or deceleration.

We deal with forces all day, every day. You travel thirty miles per hour on a four wheeler. You stop. Are you hurt? That depends on the rate of deceleration. If you stop in ten seconds you are not hurt. If you stop instantly when the four wheeler hits a tree, you very well might be.

For a planing boat, there is a critical point where the rate water is pushed away is high enough that the water seems to become “solid” and the boat gets “on step”, that is, on top of the water rather than plowing through it.

Mass vs Weight

The mass of something and the weight are different. The mass of something refers to how much matter is in the object. It has just as much mass in outer space as it does on earth. The weight refers to how much gravity is pulling on something. An object could weigh ten pounds here on earth, weigh nothing in outer space, yet the mass would be the same in both places.

As simple scientists here on earth, we often inaccurately refer to them as the same.

Acceleration

Acceleration is defined as distance (feet) per second squared.

ft/seconds2

Herein is one of the most important concepts in all science. With many forces, as one variable is increased, the result increases in the same proportion. With equations that involve acceleration, the result is squared. When a variable is increased, the result is squared or reduced by the square.

Let’s look at an example. An object with a mass of ten is at rest. It is accelerated to ten feet per second.

In one case, it is accelerated to that speed in four seconds.

In another case it is accelerated in twice that time, eight seconds.

Is the force cut by one-half because the time of acceleration is doubled? NO! The force required is reduced by one-quarter.

This explains why there is a very critical speed at which an airplane will either fly or stall. The rate at which the air is pushed out of the way is squared. The difference in lift at fifty-six mph and sixty mph can be great.

### A = R

The third law that Newton described was A = R. Every action has an equal and opposite reaction. As a bullet hits an animal, the force against the animal by the bullet is acknowledged. But the animal also exerts an equal force on the bullet. It is slowed down from very high velocity to zero velocity.

A woodsman swings an axe at a tree. The axe exerts a force against the tree. The tree exerts a force against the axe.

Each action has and equal and opposite reaction. In the above examples the reaction is damaged flesh and severed wood.

## Friction

Friction is the resistance to motion between two surfaces that are in contact. We spend much of our lives trying to increase or decrease friction. Without friction it is impossible to light a match. If we don’t avoid friction, a chainsaw might not last an afternoon. I have always regarded the understanding of friction as most important in the North. Since the wheel is very impractical without roads and hard surfaces, sleds and boats have been pushed and pulled in their respective seasons for thousands of years. Friction has made fires, hindered motion, and inserted itself into traditional life in a multitude of ways.

Friction has two causes:

1. Molecular attraction between two surfaces. The molecules actually form a slight electromagnetic bond with each other.
2. Rough surfaces interlock with each other. The rough spots on one surface mesh with the rough spots on the other. Material is ripped from each surface, and there is a constant chattering between the two materials.

There are two types of friction:

1. Static friction. Two surfaces are in contact, but are not moving against each other.
2. Sliding (kinetic) friction. Two surfaces are in contact and are moving against each other.

Static friction is greater than kinetic friction. When you get a sled going on the snow, there are two things you are overcoming:

• Inertia
• Static friction

As the sled is moving, inertia is overcome. There is kinetic friction, but kinetic friction is much less than static friction. It is easier to keep a sled moving than it is to get it in motion.

### Pressure and weight influence friction

While the friction of two surfaces can be measured, the friction can be increased or decreased by increasing or decreasing the weight or pressure between the two. If you drag a file cabinet across the floor, the friction will be reduced if the drawers are removed to reduce the pressure between the two sliding surfaces.

### Different surfaces

Different surfaces have different amounts of friction. An unpeeled log is very hard to drag through the woods. The same log peeled will drag easily. High and low friction.

There are times when we want to increase friction. We put sand or sawdust in paint on stairs to roughen the surface so we won’t slip. Brakes on snowmachines are designed to induce friction to slow down the machine. The kinetic energy of the machine is changed to heat energy in the brake.

There are times when we try to avoid friction like in bearings and on sled runners.

### Byproducts of friction

Friction is a force acting against motion. There is no movement without friction on the earth. Some movements might minimize friction, but all movements involve some amount. The byproducts of friction are mostly heat but occasionally sound. Rub your hands together when they are cold. Do they get warm? This is a product of friction. Listen to a fishwheel that isn’t lubricated. Can you hear it groan? This sound is the product of friction.

## Surface Area

Surface area is simply the area of an object that is exposed. A hand that is closed and one that is open are not different in any way except that the surface area is different. The mass, chemical composition, density, etc. are the same in both hands. Mittens and gloves cover the same hand, but their surface area is different.

Understanding surface area is important to us for three main reasons.

1. Heat transfer and loss are greatly influenced by the surface area exposed to the heat differences. A chainsaw head has fins to increase surface area to get rid of heat. A winter traveler curls his hand in his mittens to reduce the surface area that can lose heat.

2. The pressure exerted on a surface is described in terms of pounds per square inch. How many square inches is the force being exerted upon? Snowshoes increase the surface area a person’s weight is distributed upon. A knife decreases the surface area a worker’s efforts are distributed upon.

3. The surface area that is exposed where a chemical reaction can take place often determines how rapidly the reaction can occur. When we make shavings to start a fire in the morning, we are simply increasing the surface area upon which combustion can occur.

## Forms of Energy

There are six forms of energy available to the common person:

• Heat
• Light
• Chemical
• Kinetic (motion)
• Electrical
• Sound

Nuclear energy is not part of our daily lives in Alaska.

The six forms of energy can be converted, one to another. Some of the conversions are quite simple and common. Others are very difficult. Electricity converts easily to all of the other forms of energy. It would be quite difficult to convert sound to other forms of energy. This subject is addressed mostly in the section on generators.