What is science?

An introduction to physical science

PSC1515

CHAPTER 1

What is Science?

The nature of science

Ancient Greeks:

Over 2,000 years ago were philosophers. They came up with ideas (thinking only) but had no experimental evidence. For example, the idea that there were atoms and elements.

Beginning of Modern Science: ~300 years ago

• Associated with Galileo and Newton

• Additional component here - understanding based upon experimental evidence

The Scientific Method

1. Observe some aspect of nature (Observations)

2. Propose an explanation for something observed (Hypothesis)

3. Test the explanation with preliminary experiments.

4. Use the explanation to make predictions (Theory)

5. Test the predictions with more experiments or more observations

6. Modify explanation as needed

7. Return to 3.

Hypothesis

• A tentative explanation of some regularity of nature.

• e.g. water evaporates from a puddle because of the energy absorbed from the atmosphere.

• A useful hypothesis will suggest new experiments to test the hypothesis. Determine the length of time needed for the same amount of water to evaporate at different temperatures.

Experiment:• Testing natural phenomena in a controlled manner

so that the results can be duplicated and rational conclusions obtained.

• e.g. Determine the effects of temperature on the amount of carbon dioxide that dissolves in a given volume of water.

• Control temperature and observe the fizzing produced when opening a bottle of soda water at different temperatures.

Theory

• A tested explanation of basic natural phenomena.• Established after a hypothesis passes many tests.• e.g. Molecular theory of gases: All gases are composed of

very small particles called molecules.• A theory cannot be proven absolutely. It is always possible

that further experiments will show the theory to be limited or that someone will develop a better theory.

• For example, Newton’s equations about motion were found 200 years later not to apply to very small objects or objects moving near the speed of light. This led to the theory of relativity and quantum mechanics.

Example of Scientific Method

• Observations: Water boils faster than cream of mushrooms soup.

• Experiment: Place pans with equal amounts of water and different soups to heat at the same temperature and measure the time required for each to boil.

• Hypothesis: If another substance is added to water to create a mixture then it will take longer for the mixture to boil.

• Theory: The higher the density of a water based mixture the longer it will take to boil.

The Scientific MethodObservations

Hypothesis

Experiments

Negative Results Positive Results

Theory

Further Experiments

Negative Results Positive Results

Scientific Law

• A concise statement or mathematical equation about a fundamental relationship or regularity of nature

• e.g. The law of conservation of mass and energy: Mass (quantity of matter) remains constant during

any chemical change. • A law is established after a series of experiments,

when a researcher sees some relationship or regularity in the results.

Measurements

Compared to a reference called a Unit.

How much and of what.

(Number (Name of

Quantity) Unit)

e.g. 15.7 inches

Two major systems for measurements:

• English System-Used mostly in U.S.. Problems associated with international trade. There is pressure to convert to the metric system.

• Metric System-Used worldwide. Both systems are in use in the U.S..

• For scientific purposes the metric system is used almost exclusively.

The Metric System

• Established by the French Academy of Sciences in 1791.

• Based in invariable referents in nature.

• Redefined over time to make the standard units more reproducible.

• The International System of Units (SI) is a modernized metric system.

Seven Standard Units:

All other units are derived units; e.g. area, volume, speed

Standard metric units for the 4 fundamental properties

Length (m)• Distance light travels in seconds

Mass (kg)• Referenced to standard metal cylinder

Time (s)• Referred to oscillation of cesium atom

Charge

All other properties (e.g. area, volume, etc.) derived from these

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Length

• The meter is the standard unit of length.

• It is abbreviated “m”.

• It is slightly longer than a yard.

• 1 yard=36 inches, 1 meter=39.3 inches

• Many doorknobs are approximately 1 meter from the floor.

Mass• Kilogram is the standard unit.• It is abbreviated kg.• It is the only standard unit still defined in terms of

an object, a metal cylinder kept by the Intl. Bureau of Weights and Measurements in France.

• Mass and Weight are proportional but are not the same thing.

• Mass is a measure of the inertia on an object, the tendency to maintain a state of rest or straight line motion.

• Weight is a measure of the force of gravity on an object.

• The numerical values for mass an weight on earth are usually the same, but the units are different.

Metric prefixes are used to represent larger or smaller amounts by factors of 10.

Need to know:k, d, c, m, μ

Metric prefixes

• Simplify the conversion process

• Help avoid writing large or small numbers

Length (l): The distance between two points

• 10 decimeters (dm) = 1 meter (m)

• 10 centimeters (cm)=1 decimeter (dm)

• 10 millimeters (mm)=1 centimeter (cm)

• 1000 micrometers (μm)=1 millimeter (mm)

(pronounced “micro”)

• 1000 meters (m)= 1 kilometer (km)

Area(A): The extent of surface. (Two dimensional)

• Length (l) times width (w). A= l x w

• Resulting area is in square length units.

• e.g. 10 cm long and 30 cm wide gives:

A=l x w

A=10 cm x 30 cm = 300 cm2

Volume (V): The capacity of an object.

• Length (l) times width (w) times height (h)

V=l x w x h

• Units are cubic length units.

• e. g. a prism is 20 cm long, 45 cm wide, and 15 cm high.

V=20 cm x 45 cm x 15 cm

V= 13500 cm3

Volume-Cube

Volume of a Cube

• 1 cubic decimeter (dm3) is 1 dm or 10 cm on each side.

• The volume of a cube 10 cm on each side is: V= 10 cm x 10 cm x 10 cm

V= 1000 cm3 V= 1 dm x 1 dm x 1 dm V= 1 dm3

• 1 dm3= 1 liter (L)• 1 cm3 = 1 milliliter (mL)

Density Ratio

• Density (ρ )(pronounced “rho”) is a ratio of the mass of an object to its volume.

• It is the mass of an object per unit of volume.• 1 dm3 of water has a mass of 1 kg.• Since 1 dm3=1000 cm3, 1000 cm3 of water have a mass of 1 kg.• Consequently, 1 cm3 of water has a mass of 1 g.• The density of water is: ρ = m/V ρ=1 g/ 1 cm3 or 1 kg / 1 dm3

ρ=1 g/cm3 or 1 kg / dm3

ρ=1 g/mL or 1 kg / L

The density ratio

• Ratio of mass and volume

• Intrinsic property (independent of quantity)

• Characteristic of a given material

Calculating Density

• ρ = m/V• Object with a mass of 10 g and a volume of

5 cm3: ρ = 10 g / 5 cm3

ρ =2 g/cm3

• Any unit of mass and any unit of volume can be used. For example, it could be pounds per gallon (lbs./gal)

Calculating Density

• Density (ρ) for a liquid is usually expressed in grams/milliliter (g/mL)

• Density for a solid is usually expressed in grams/cubic centimeter (g/cm3).

• Block 1 has a mass of 47.5 g and a volume of 4.17 cm3.• Block 2 has a mass of 63.2 g and a volume of 7.05 cm3.• Density for Block 1: ρ =47.5 g/4.17 cm3

ρ = 11.4 g/ cm3

Density for Block 2: ρ =63.2 g/7.05 cm3

ρ = 8.96 g/ cm3

Calculating Density

• If these are in table 1.4, what are they?

Block 1 is lead, block 2 is copper.

Symbols and equations

Symbols• Represent quantities, measured properties

Equations • Mathematical relationships between properties

• Describe properties; define concepts; specify relationships

Some common symbols

• ρ = density

• m= mass

• V=volume

• A = area

• l=length

• w=width

• h=height

• T=temperature

• T1=initial temperature

• T2=final temperature

• Δ =change (delta)

T2-T1= ΔT

• =therefore

• = proportional to

Equations

• Equations are used for:

1. Defining a property. e.g. ρ = m/V 2. Defining a concept: e.g. v=d/t 3. Defining how quantities change with

respect to one another (their relationship): e.g. The Ideal Gas Law: PV=nRT, where P is pressure, n is moles (quantity of gas), and R is a constant.

Equations:

• Relationships between variables.

• A variable is a specific quantity of an object or event that can have different values; e.g. your weight, heartbeats, breaths per minute, blood pressure.

Movie representing orders of magnitude

http://www.micro.magnet.fsu.edu/primer/java/scienceopticsu/powersof10/

Relationships Between Variables:• Direct Proportion: One variable increases and the other

variable also increases; e.g. Weight changes in response to the food you eat. If all other factors are equal, the more food you eat the larger your weight gain.

Also, F = m x a where F is force and a is acceleration. If m is constant, then F a• Inverse Proportion: One variable increases while the

other variable decreases; e.g. Pressure (P) increases when volume decreases

P 1/V

Proportionality Statement• The larger the volume of the gas tank, the longer it takes to

fill. V t.

V = k t where k is a proportionality constant. k must have units of L/min here.

L=L/min x min L=L

• It is also possible to have numerical constants which contain no units.

= 3.14

A== r2 where A=Area and r = radius.

Units: m2 = m2

Problem Solving

• Read problem and make a list of the variables with their symbols on the left side of the page.

• Inspect the list of variables and the unknowns and identify the equation that expresses a relationship between the variables.

• If needed solve the equation for the variable in question.• If needed convert unlike units so they are all the same,

such as if time is in seconds distance is desired in m, and speed is in km/hr then it should be converted to m/s.

• Substitute the number value and unit for each symbol in the equation (except the unknown)

• Perform math operations on the numbers and the units.• Get answer.

Example 2 of Problem Solving

• A metal has a density of 11.8 g/cm3. What is the volume of a piece of this metal with a mass of 587 g?

=11.8 g /cm3 = m/V

m=587 g m= x V

V=? cm3 V = m/

V = 587 g/11.8 g/cm3

V = 49.7 cm3

Precision and Accuracy in Measurement

• Precision is a measure of how reproducible a measurement is. The closer different measurements are of the same thing the more precise they are. 4.76 g, 4.86 g, 4.81 g are more precise than 4.76 g, 4.98 g, 5.15 g.

• Accuracy is a measure of how close a measurement is to the accepted value for that measurement. A calculation of the density of water which gives you .98 g/mL is more accurate than 1.11 g/mL, since the accepted value for the density of water is 1.00 g/mL.

• % Error is a measure of the accuracy of a measurement. • %error = [(measured value-accepted value)/accepted value]x100• For 1.11 g/mL % error= [(1.11 g/mL-1.00 g/mL)/1.00 g/mL] x 100 %error=11% For .98 g/mL % error= [(.98 g/mL-1.00 g/mL)/1.00 g/mL] x 100 %error=2% (Make the number positive)

Review for Ch. 1

• The Scientific Method: Observations Hypothesis Experiments Theories Scientific Law• Measurements English System Metric System Metric Units Metric Prefixes Area and Volume 1 L and 1 mL volumes (cubes)

• Density Calculating Density Density of Water• Symbols and Equations Solving for an unknown quantity Common symbols for units• Accuracy and Precision

Do problems p.1-21 and 1-22 #1, 4, 5, 7, 9, 11, 12, 13, 14, 15, 16, 17, 18.

#1-10 Group A p. 23• New Book: p. 23 # 3, 4, 5, 6, 7, 8, 9, 10, 11, 12,

13, 15, 16, 19, 20, 21, 22, 23, 25, 26, 27, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 44, 46

p. 27 # 2, 3, 4, 5, 6, 7, 8