Summary

Grade 7 - 9 Topics in Physical Science - Physics of Motion

Solving Word Problems Word problems depict a realistic situation. Word problems are used to express situations that we actually face in everyday life. It is very important to learn how to approach and solve such problems.• Steps to Use When Solving Word Problems• • 1. Define the problem: Write out in your own words the question that is being asked. • • 2. Write down all the information given: Make sure you clearly write out ALL the information that is given in the problem.• • 3. Select relevant information: Select the relevant information needed to solve the problem from all the information.• • 4. Draw a diagram: Draw a simple diagram that represents the problem. Make sure you label all the relevant values, such as distance,

time, elevation, strength of a force, etc. • • 5. Write down the relevant relationships: Write down clearly all the relevant information you know regarding theories, relationships and

equations that might be useful in solving the problem. • • 6. Makes a logical estimate of your answer: Using scientific reasoning and basic mathematical relationships, make a logical estimate of

what you think the answer should be. You can't estimate the exact answer, but you can get a rough estimate in terms of how large or small the number should be.

• • 7. Solve the problem: Solve the problem using the information and relationships available to you.• • 8. Check your answer to see if it makes sense: For example, if your estimate in step 5 indicates the answer must be greater than 1, but

your answer is less than 1, you know you did something wrong. If your answer doesn't make sense, go back to step 1 and review what you did to see if you made a mistake.

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Concept of Dimensions and Units• Dimension is a measurable characteristic. Dimensions are used to describe the state or conditions of the physical

world around us. Sometimes dimensions are referred to as a physical quality. Some examples of dimensions are length, mass, time, electric charge, area, speed, force, and weight.

• • Two types of dimensions. • Fundamental dimensions describe the basic characteristics of the universe. • • Mass, Space (length) Time• • Derived dimensions describe more complex characteristics of the universe that are made up of various

combinations of fundamental dimensions. • • Velocity, Acceleration, Force• • Unit is an agreed upon standard for measuring a dimension. It allows us to give a numerical value to a dimension.

Sometimes dimensions are referred to as a physical quantity. Some examples of units are kilograms, feet, meters, seconds, minutes, square feet, square meters, miles per hours, meters per second and pounds.

• • For example, mass (m) is a dimension and kilogram (kg) is a unit. Mass is the "measurable characteristic" being

described by the "standard" or "unit" kilogram. To describe a quality of mass properly you need to have the number value and units such as 6 grams.

• • PLEASE, ALWAYS REMEMBER that an answer is WRONG if the units are incorrect.

System of Units• In science the standard of units is called the

International System of Units or SI system. • This system is often called the metric system because

many of the SI units were derived from the metric system.

• Some examples of SI units are kilograms, meters and seconds. – The SI units are very logical in that they use prefixes based

upon powers of 10 to describe large and small quantities. One tenth (1/10) of a meter is a decimeter and 1/100 of a meter is a centimeter. For example, a decameter is 10 meters; a hectometer is 100 meters.

• The other system of measurement we commonly use in the United States is called the English system. It uses units such as pounds, feet, and seconds. Since we use both systems in this country, we will use both in this course.

Table of Metric or SI Prefixes.Prefix: Symbol: Magnitude: Meaning (multiply by):

Yotta- Y 1024 1 000 000 000 000 000 000 000 000

Zetta- Z 1021 1 000 000 000 000 000 000 000

Exa- E 1018 1 000 000 000 000 000 000

Peta- P 1015 1 000 000 000 000 000

Tera- T 1012 1 000 000 000 000

Giga- G 109 1 000 000 000

Mega- M 106 1 000 000

myria- my 104 10 000 (this is now obsolete)

kilo- k 103 1000

hecto- h 102 100

deka- da 101 10

None None 100 1

deci- d 10-1 0.1

centi- c 10-2 0.01

milli- m 10-3 0.001

micro- u (mu) 10-6 0.000 001

nano- n 10-9 0.000 000 001

pico- p 10-12 0.000 000 000 001

femto- f 10-15 0.000 000 000 000 001

atto- a 10-18 0.000 000 000 000 000 001

zepto- z 10-21 0.000 000 000 000 000 000 001

yocto- y 10-24 0.000 000 000 000 000 000 000 001

• A fundamental unit is the agreed upon standard for measuring a fundamental dimension.

• Below is a table of SI and English fundamental units.

Dimension SI English

Mass kilogram (kg) slug, pound

Space meter (m) foot (ft)

Time second (s) second (s)

Derived and Composite Dimensions and Units

• Composite dimensions are combinations of the same dimension and

• Derived dimensions are combinations of different dimensions.

• ALL composite and derived variables have their associated units.

Table of some SI and English composite and derived units.

Dimension SI English

Area square meters (m2) square feet (ft2)

Volume cubic meters (m3) cubic feet (ft3)

Speed and Velocity

meters per second(m/s)

miles per hour(mph)

Acceleration meters per second per second (m/s2)

miles per hour/ second (mph/s)

Force and Weight Newton (N) pound (lbs)

Concept of Scalars and Vectors• Scalars are quantities that can be fully described by

magnitude, size, or amount alone. Scalars don't have a direction associated with them. – For example, we only need a number and a unit, such as 0

C, 32 F or 273 K to fully describe temperature

• Vectors, on the other hand, are quantities that need a magnitude, size, or amount and a direction to fully describe them. – For example, to fully describe a velocity we must have a

magnitude and a direction such as 40 mph south or 3 m/s up. It is important to note that every vector can be broken into a scalar part (component) and a direction.

Physics of Motion • 3.1 Distance and Displacement• • Distance and displacement are two quantities that may

seem to mean the same thing, yet they have distinctly different meanings and definitions in science.

• • Distance is a scalar quantity that refers to "how much space

an object has moved through" during its motion. • • Displacement is a vector quantity that refers to "how far an

object has moved from its original position. So, it describes the object's change in position.

Speed, Velocity, and Acceleration

• Speed is a scalar quantity that refers to how fast an object is moving (rate at which an object changes its position) without respect to direction. Example 30 miles/hour

• • Velocity is a vector quantity that refers to how fast an object is moving

plus its direction. Example 30 miles/hour east. Note that speed is the magnitude of velocity.

• • Acceleration is a vector quantity that is defined as "the rate at which an

object changes its velocity." Any object is accelerating if it is changing its velocity. Keep in mind – Direction is part of velocity, so just changing direction is also an acceleration.

• In science, slowing down is a form of acceleration, where the value of acceleration is negative. – So, de-acceleration is just an acceleration that is negative. Energy

Relationships

• Physics of Forces • 4.1. Basic Definitions of Force• • A force is a push or pull upon an object resulting from the object's interaction with another object. Whenever

there is an interaction between two objects, there is a force upon each of the objects. When the interaction ceases, the two objects no longer experience the force. Forces only exist as a result of an interaction. It take a force to change the motion of an object, which is another way of saying it take a force to accelerate an object. The very famous and useful relationship Newton discovered was a that the amount of Force = Mass times Acceleration or F = ma which is now called Newton's second law of motion.

• • For simplicity sake, all forces (interactions) between objects can be placed into two broad categories:• • Contact forces • Action-at-a-distance forces• • Contact forces are types of forces in which the two interacting objects are physically contacting each other.

Examples of contact forces include frictional forces, tensional forces, normal forces, air resistance forces, and applied forces.

• • Action-at-a-distance forces are types of forces in which the two interacting objects are not in physical contact with

each other, yet are able to exert a push or pull despite a physical separation. Examples of action-at-a-distance forces include gravitational forces, magnetic forces and electric forces.

• Physics of Forces • 4.1. Basic Definitions of Force• • A force is a push or pull upon an object resulting from the object's interaction with another object. Whenever

there is an interaction between two objects, there is a force upon each of the objects. When the interaction ceases, the two objects no longer experience the force. Forces only exist as a result of an interaction. It take a force to change the motion of an object, which is another way of saying it take a force to accelerate an object. The very famous and useful relationship Newton discovered was a that the amount of Force = Mass times Acceleration or F = ma which is now called Newton's second law of motion.

• • For simplicity sake, all forces (interactions) between objects can be placed into two broad categories:• • Contact forces • Action-at-a-distance forces• • Contact forces are types of forces in which the two interacting objects are physically contacting each other.

Examples of contact forces include frictional forces, tensional forces, normal forces, air resistance forces, and applied forces.

• • Action-at-a-distance forces are types of forces in which the two interacting objects are not in physical contact with

each other, yet are able to exert a push or pull despite a physical separation. Examples of action-at-a-distance forces include gravitational forces, magnetic forces and electric forces.

• 4.2.2. Derived Forces and Energy• • Derived forces and energy are forces and energy that result from some combination or interaction of the

fundamental forces. • • Mechanical forces and energy are those forces and energy that are the result of the motion or kinetic energy of an

object. • • Thermal forces and energy are those forces and energy that result because of heating or cooling.• • Electrical and magnetic forces and energy are those forces and energy that result because of an electric current we

call electricity. Forces, Motion, Pressure, Work and Energy• • 4.2. Pressure• • Pressure is the force per unit area, and it is typically measured in pounds per square inch. Or, • PRESSURE = FORCE/AREA • P = F/A• • Force is created by pressure exerted on an area. Or, • FORCE = PRESSURE x AREA • F = P x A