Introduction to Scientific Method

Steps in scientific method 1. Determine the problem. 2. State the hypothesis. 3. Design & perform experiment to test your hypothesis and collect data. 4. Analyze data. 5. Draw conclusions. Steps in scientific method

a prediction about a problem that can be tested. IF…THEN statement. Hypothesis: a prediction about a problem that can be tested. IF…THEN statement. For example: when you investigate erosion of soil, a possible hypothesis could be: “if grass is planted on soil, then the soil erodes more. slowly.” Hypothesis

Observations Qualitative - done through senses – (color, smell). Example: red, large, smells like peppermint, cold. Observations

Quantitative - collected using measurements Quantitative - collected using measurements. Example - mass, volume, density, temperature, composition. 10.3 g, 100C. Observations

When scientists design an experiment, they need to follow certain guidelines to reduce chances of getting wrong conclusions. They need something to compare their results with, or a standard for comparison. It is called control. Control

When the experiment is conducted, scientists study only one factor at a time. All other conditions should remain the same between all batches of samples. All factors kept the same are called constants. Constants

Variables Variable - something that changes in the experiment. independent variable (iv) = controlled by the experimenter (you) dependent variable (dv) = changes because of the id (independent variable). It depends on something else. Variables

Cause-effect relationship presence of grass Cause Effect Effect: amount of erosion Independent Variable Dependent Variable

Common measurements and their SI units Mass - kilogram (kg), gram (g) Volume - liter (L), milliliter (mL) Density - g/mL Temperature - degree Celsius (C), Kelvin (K)

Add to Table of Contents Scientific Method Notes

When graphing: to compare values use bar graph to show trends use line or x-y graph

Independent variable - plotted on the horizontal (x) axis dependent variable - plotted on the vertical (y) axis

Experimental design An experiment was designed to investigate the effect of caffeine on the heartbeat of Daphnia. Two populations of Daphnia were cultured. Both populations had water with the same mineral content, were supplied with identical amounts of bacteria as food, received the same amount of light, and had their temperature maintained at 20°C. Every two hours Daphnia from both populations were selected and their heartbeats were monitored. The Daphnia of population one had caffeine administered five minutes before the heartbeat was checked. The Daphnia of population two were given nothing.

control An experiment was designed to investigate the effect of caffeine on the heartbeat of Daphnia. Two populations of Daphnia were cultured. Both populations had water with the same mineral content, were supplied with identical amounts of bacteria as food, received the same amount of light, and had their temperature maintained at 20°C. Every two hours Daphnia from both populations were selected and their heartbeats were monitored. The Daphnia of population one had caffeine administered five minutes before the heartbeat was checked. The Daphnia of population two were given nothing.

constants An experiment was designed to investigate the effect of caffeine on the heartbeat of Daphnia. Two populations of Daphnia were cultured. Both populations had water with the same mineral content, were supplied with identical amounts of bacteria as food, received the same amount of light, and had their temperature maintained at 20°C. Every two hours Daphnia from both populations were selected and their heartbeats were monitored. The Daphnia of population one had caffeine administered five minutes before the heartbeat was checked. The Daphnia of population two were given nothing.

Independent variable An experiment was designed to investigate the effect of caffeine on the heartbeat of Daphnia. Two populations of Daphnia were cultured. Both populations had water with the same mineral content, were supplied with identical amounts of bacteria as food, received the same amount of light, and had their temperature maintained at 20°C. Every two hours Daphnia from both populations were selected and their heartbeats were monitored. The Daphnia of population one had caffeine administered five minutes before the heartbeat was checked. The Daphnia of population two were given nothing.

Dependent variable An experiment was designed to investigate the effect of caffeine on the heartbeat of Daphnia. Two populations of Daphnia were cultured. Both populations had water with the same mineral content, were supplied with identical amounts of bacteria as food, received the same amount of light, and had their temperature maintained at 20°C. Every two hours Daphnia from both populations were selected and their heartbeats were monitored. The Daphnia of population one had caffeine administered five minutes before the heartbeat was checked. The Daphnia of population two were given nothing.

Independent variable Dependent variable DATA TABLE

Experimental design Students investigated how temperature of soil affects germination. They measured number of seeds that germinated over ten days. The control group was kept at 18C and the experimental group at 25C. Examine the graph and answer: What is the independent variable? What is the dependent variable? Which group is a control? What are the constants?

Type of observations Scientific observations are either qualitative or quantitative.

Qualitative observations Qualitative observations are done through our senses. We give a description of what is happening by noting a change in shape, color, smell, objects becoming warmer/colder, larger/smaller, etc.

Quantitative observations Quantitative observations are measurable quantities, always collected using instruments. For example mass, temperature, volume, density, chemical composition, etc. These observations (measurements) always specify the unit of measurement. For example 10.5 grams, 0.33 mL, 100C.

Some measurable properties and their units Mass - quantity of matter within a sample Volume – amount of space occupied by matter Length – the distance between two points energy of particles in the object SI unit is kilogram (kg) SI unit is liter (L), milliliter (mL)= cm3 SI unit is meter (m)

Some measurable properties and their units Temperature – the measure of how hot or cold object is; the measure of the average kinetic energy of particles in the object SI unit is Kelvin (K), also degree Celsius (C)

Some measurable properties and their units Density – describes how the molecules of the substance are packed; the mass of object divided by volume SI unit is g/mL or g/cm3

Theory and Scientific Law Theory is explanation based on the results of repeated tests, experiments and observations Examples: theory of plate tectonics, theory of evolution, kinetic theory of matter Theories serve as explanations of scientific laws. They can be changed or discarded when new observations show them to be incorrect

Theory and Scientific Law Law is a scientific rule of nature that describes the behavior of something in nature, but doesn’t explain the relationship. Examples: law of conservation of mass, law of gravitation, Boyle’s gas law, etc. Laws are used to predict what will happen in a given situation.

Measurements in science Scientific notation In scientific notation a number is expressed as the product of two numbers: a coefficient and 10 raised to a power 1.67  10-24 6.022 x 1023

Units of Measurement SI Units There are two types of units: fundamental (or base) units; derived units. There are 7 base units in the SI system.

Powers of ten are used for convenience with smaller or larger units in the SI system.

SI Units

There are three temperature scales: Kelvin Scale SI Units Note the SI unit for length is the meter (m) whereas the SI unit for mass is the kilogram (kg). 1 kg weighs 2.2046 lb. Temperature There are three temperature scales: Kelvin Scale Used in science. Same temperature increment as Celsius scale. Lowest temperature possible (absolute zero) is zero Kelvin. Absolute zero: 0 K = -273.15 oC.

Temperature Celsius Scale Fahrenheit Scale Also used in science. Water freezes at 0 oC and boils at 100 oC. To convert: K = oC + 273.15. Fahrenheit Scale Not generally used in science. Water freezes at 32 oF and boils at 212 oF. To convert:

Temperature

Derived Units Derived units are obtained from the 7 base SI units. Example:

Density Used to characterize substances. Defined as mass divided by volume: Units: g/cm3 (same as g/mL) Expresses packing of molecules In most cases density increases with the decrease in temperature (water is an exception)

Dimensional Analysis Method of calculation utilizing a knowledge of units. Given units can be multiplied or divided to give the desired units. Conversion factors are used to manipulate units: Desired unit = given unit  (conversion factor) The conversion factors are simple ratios:

Dimensional Analysis Using Two or More Conversion Factors Example to convert length in meters to length in inches:

Dimensional Analysis Using Two or More Conversion Factors In dimensional analysis always ask three questions: What data are we given? What quantity do we need? What conversion factors are available to take us from what we are given to what we need?