UNIT 1 Forces and Motion
WHY DO THE PLANETS MOVE THE WAY THEY DO? Watch the following video clip and generate a list of possible answers to the question or observations. https://www.youtube.com/watch?v=g53A5aG 6oyQ
THINKING ABOUT OUR DISCUSSION, ANSWER THE FOLLOWING QUESTIONS What causes the planets/Earth to move the way they do? What factors affect the motion of an object? How can you change the motion of an object? What do you need to know in order to understand the motion? (think about how we could test it)
INTRODUCTION TO SCIENCE AND THE SCIENTIFIC METHOD Day 1
WRITING A LAB PROCEDURE ACTIVITY
WHAT IS SCIENCE? The goal of science is to investigate and understand the natural world, to explain events in the natural world, and to use those explanations to make useful predictions.
SCIENCE: Science deals only with the natural world. Scientists collect and organize information in a careful, orderly way, looking for patterns and connections between events. Scientists propose explanations that can be tested by examining evidence. Science is an organized way of using evidence to learn about the natural world.
HOW IS SCIENCE DONE? Science begins with an observation. This is the process of gathering information about events or processes in a careful, orderly way. Data is the information gathered from making observations. There are two types of data: Quantitative data are numbers and are obtained by counting or measuring. Qualitative data are descriptions and involve characteristics that cannot be counted. Hypothesis A hypothesis is a scientific explanation for a set of observations. A hypothesis must be stated in a way that makes it “testable”. The hypothesis is just a possible answer to a question, and it must be thoroughly tested.
SCIENTIFIC METHODS The scientific method is a series of steps used by scientists to solve a problem or answer a question. The Steps to the Scientific Method
OBSERVATION / ASKING A QUESTION A problem or a question must first be identified. Examples: How much water can a root hair absorb? Why does a plant stem bend toward the light? What effect does temperature have on heart rate?
FORM A HYPOTHESIS Hypothesis: A possible explanation to the question or problem. It is simply a prediction and has not yet been proven or disproven. It must be stated in a way that is testable. A statement is considered “testable” if evidence can be collected that either does or does not support it.
DESIGNING A CONTROLLED EXPERIMENT The factors in an experiment that can be changed are called variables. Some example of variables would be: changing the temperature, the amount of light present, time, concentration of solutions used. A controlled experiment works with one variable at a time. If several variables were changed at the same time, the scientist would not know which variable was responsible for the observed results. In a “controlled experiment” only one variable is changed at a time. All other variables should be unchanged or “controlled”.
An experiment is based on the comparison between a “control group” with an “experimental group”. These two groups are identical except for one factor. The control group serves as the comparison. It is the same as the experiment group, except that the one variable that is being tested is removed. The experimental group shows the effect of the variable that is being tested.
Example: In order to test the effectiveness of a new vaccine, 50 volunteers are selected and divided into two groups. One group will be the control group and the other will be the experimental group. Both groups are given a pill to take that is identical in size, shape, color and texture. Describe the control group: Even though they are given identical looking pills, the control group will not actually receive the vaccine. Describe the experimental group: This group is receiving the vaccine. What variables are kept constant? The size, shape, color, and texture of the pill. What variable is being changed? Whether or not the pill contains any vaccine.
There are two variables in an experiment: The independent variable is the variable that is deliberately changed by the scientist. The dependent variable is the one observed during the experiment. The dependent variable is the data we collect during the experiment. This data is collected as a result of changing the independent variable. In the above example, what is the independent variable? The addition of the vaccine to the pills that were given to the volunteers. In the above example, what is the dependent variable? The observed health of the people receiving the pills.
Step 4: Recording and Analyzing Results The data that has been collected must be organized and analyzed to determine whether the data are reliable. Does the data support or not support the hypothesis? Step 5: Drawing Conclusions The evidence from the experiment is used to determine if the hypothesis is proven or disproven. Experiments must be repeated over and over. When repeated, the results should always be the same before a valid conclusion can be reached.
FORMING A THEORY A theory may be formed after the hypothesis has been tested many times and is supported by much evidence. Theory: A broad and comprehensive statement of what is thought to be true. A theory is supported by considerable evidence.
PRACTICE PROBLEM You want to determine the effects of a certain fertilizer on the growth of orchids grown in a greenhouse. Materials that are available to you include: greenhouse, 100 orchid plants, water, fertilizer, and soil. You want to know if the orchids will grow best with a weak concentration of fertilizer, a medium concentration of fertilizer, or a high concentration of fertilizer. How will you design an experiment to test different concentrations of this fertilizer?
STATE YOUR HYPOTHESIS: I predict that the orchids will grow best with a medium concentration of fertilizer.)
HOW WILL YOU SET UP A CONTROLLED EXPERIMENT? The 100 plants will be divided into 4 groups as follows: Group 1: 25 plants will receive plain water Group 2: 25 plants will receive a weak concentration of fertilizer Group 3: 25 plants will receive a medium concentration of fertilizer Group 4: 25 plants will receive a high concentration of fertilizer The plants will be watered daily. Over a period of a month, the plants will be measured to see which ones grew the tallest.
WHAT IS THE CONTROL GROUP IN THIS EXPERIMENT? The control group consists of the 25 plants that are receiving plain water.
WHAT IS THE EXPERIMENTAL GROUP IN THIS EXPERIMENT? The experimental group consists of the 75 plants that are receiving various concentrations of fertilizer.
WHAT VARIABLES MUST BE KEPT CONSTANT IN THIS EXPERIMENT? All plants receive the same amount of fluid each day. All plants are grown in pots of equal size. All plants are grown at the same temperature. All plants receive the same amount of sunlight.
WHAT VARIABLE IS BEING CHANGED IN THIS EXPERIMENT? The variable being changed is the amount of fertilizer.
AFTER ONE MONTH OF MEASURING THE ORCHIDS, THE FOLLOWING DATA IS OBTAINED: Group 1 (Control Group): Grew to an average height of 15 cm. Group 2 (Weak concentration): Grew to an average height of 35 cm. Group 3 (Medium concentration): Grew to an average height of 28 cm. Group 4 (High concentration): Grew to an average height of 10 cm.
IS YOUR HYPOTHESIS SUPPORTED OR DISPROVED BY THESE RESULTS? We hypothesized that the orchids would grow best with a medium concentration of fertilizer. The results do not support this. The results disprove our hypothesis.
WHAT IS YOUR CONCLUSION BASED ON THESE RESULTS? Orchids grow best with a weak concentration of fertilizer. At medium to high concentrations, plant growth is inhibited.
ANALYSIS QUESTIONS: Answer the questions with the person you share a table with.
WHY IS IT IMPORTANT TO HAVE A LARGE SAMPLE SIZE IN ANY EXPERIMENT? It is important to test a large sample in order to get a true picture of the results of the experiment. If the sample size is too small, an inaccurate conclusion may be reached. Results obtained by testing a large number of individuals would be much more accurate than if only a few individuals had been tested.
WHY IS IT IMPORTANT TO REPEAT THE EXPERIMENT MANY TIMES? Experiments should be repeated to see if the same results are obtained each time. This gives validity to the test results.
WHAT IS THE IMPORTANCE OF THE CONTROL? The control shows what will happen when the experimental factor is omitted. Without the control, there would be no basis for comparison and you would not know how the experimental factor affected the results.
HOW IS A THEORY DIFFERENT THAN A HYPOTHESIS? A hypothesis is an “educated guess” that is testable through observations and experimentation. A theory is a broad statement of what is believed to be true based on many experiments and considerable amounts of data.
WHY IS IT SO IMPORTANT THAT A SCIENTIST ACCURATELY DESCRIBES THE PROCEDURE USED IN THE EXPERIMENT? It allows other scientists to repeat the experiment and verify the results.
WHAT IS THE DIFFERENCE BETWEEN THE INDEPENDENT AND THE DEPENDENT VARIABLES IN AN EXPERIMENT? The independent variable is the variable that is deliberately changed by the scientist. The dependent variable is the one observed during the experiment. The dependent variable is the data we collect during the experiment.
IN A “CONTROLLED EXPERIMENT”, WHY MUST ALL OF THE VARIABLES, EXCEPT ONE, BE KEPT CONSTANT THROUGHOUT THE EXPERIMENT? If several variables were changed at the same time, the scientist would not know which variable was responsible for the observed results. Notes from Amy Brown from TPT
DATA TABLES In most cases, the independent variable (that which you purposefully change) is in the left column. the dependent variable (that which you measure) with the different trials is in the next columns, and the derived or calculated column (often average) is on the far right. Reaffirm that rows are a series of horizontal cells and that columns are a series of vertical cells.
ANALYZING A GRAPH When analyzing data, a graph gives a pictorial of the data to make understanding the relationship between the dependent variable.
GRAPHING NOTES
Graphing in Science
How to make a graph The first thing you need to do before making any graph in science is collect data. A graph is a visual representation of the data you collect in the lab.
Graphing Whenever making a graph you need to decide the type of graph that you will use. The two main graphs we will use in science are a bar graph and a line graph.
Bar Graphs Bar graphs are used to compare things between different groups or to track changes over time. For example: if you are comparing scores on a test between different classes and want to show how each class performed.
Line Graphs Line graphs are used to track changes over short and long periods of time. When smaller changes exist, line graphs are better to use than bar graphs. For example: You would use a line graph when wanting to show how the temperature of a mixture changes during a chemical reaction
Scatter Plots To determine a correlation, look for a relationship between the data sets! If there is a correlation, draw a trend line that is: 1. … as close to each data point as possible. 2. … has about the same number of points on each side of it. 3. …goes directly through at least two points.
Rules for Making a Graph Whenever making a graph, the independent variable goes on the x-axis and the dependent variable goes on the y-axis. Graphs must always have a title. Typically, we write the title of a graph as whatever is on the y-axis vs. whatever is on the x-axis. The title of the graph needs to clearly tell the reader what the data on the graph is representing.
Significant Figures (digits) = reliable figures obtained by measurement = all digits known with certainty plus one estimated digit
Taking the measurement Is always some uncertainty Because of the limits of the instrument you are using
EXAMPLE: mm ruler Is the length of the line between 4 and 5 cm? Yes, definitely. Is the length between 4.0 and 4.5 cm? Yes, it looks that way. But is the length 4.3 cm? Is it 4.4 cm? Let’s say we are certain that it is 4.3 cm or 43mm, but not at long as 4.4cm. So – we need to add one more digit to ensure the measurement is more accurate. Since we’ve decided that it’s closer to 4.3 than 4.4 it may be recorded at 4.33 cm.
It is important to be honest when reporting a measurement, so that it does not appear to be more accurate than the equipment used to make the measurement allows. We can achieve this by controlling the number of digits, or significant figures, used to report the measurement.
As we improve the sensitivity of the equipment used to make a measurement, the number of significant figures increases. Postage Scale 3 g 1 g 1 significant figure Two-pan balance 2.53 g 0.01 g 3 significant figures Analytical balance 2.531 g 0.001g 4 significant figures
Which numbers are Significant? 5,551,213 55.00 mm Which numbers are Significant? How to count them! 9000 L 0.003g
Non-Zero integers Always count as significant figures 1235 has 4 significant digits
Zeros – there are 3 types Leading zeros (place holders) The first significant figure in a measurement is the first digit other than zero counting from left to right 0.0045g (4 is the 1st sig. fig.) “0.00” are place holders. The zeros are not significant
Captive zeros Zeros within a number at always significant – 30 Captive zeros Zeros within a number at always significant – 30.0809 g All digits are significant
Trailing zeros – at the end of numbers but to the right of the decimal point 2.00 g - has 3 sig. digits (what this means is that the measuring instrument can measure exactly to two decimal places. 100 m has 1 sig. digit Zeros are significant if a number contains decimals
Exact Numbers Are numbers that are not obtained by measuring Referred to as counting numbers EX : 12 apples, 100 people
Exact Numbers Also arise by definition 1” = 2.54 cm or 12 in. = 1 foot Are referred to as conversion factors that allow for the expression of a value using two different units
Significant Figures Rules for sig figs.: Count the number of digits in a measurement from left to right: Start with the first nonzero digit Do not count place-holder zeros. The rules for significant digits apply only to measurements and not to exact numbers Sig figs is short for significant figures.
Determining Significant Figures State the number of significant figures in the following measurements: 2005 cm 4 0.050 cm 2 25,000 g 2 0.0280 g 3 25.0 ml 3 50.00 ml 4 0.25 s 2 1000 s 1 0.00250 mol 3 1000. mol 4
Rounding Numbers To express answer in correctly Only use the first number to the right of the last significant digit
Rounding Always carry the extra digits through to the final result Then round EX: Answer is 1.331 rounds to 1.3 OR 1.356 rounds to 1.4
Rounding off sig figs (significant figures): Rule 1: If the first non-sig fig is less than 5, drop all non-sig fig. Rule 2: If the first sig fig is 5, or greater that 5, increase the last sig fig by 1 and drop all non-sig figs. Round off each of the following to 3 significant figures: 12.514748 12.5 0.6015261 0.602 14652.832 14,700 192.49032 192
Math Problems w/Sig Figs When combining measurements with different degrees of accuracy and precision, the accuracy of the final answer can be no greater than the least accurate measurement.
Adding and Subtracting Sig. Figures This principle can be translated into a simple rule for addition and subtraction: When measurements are added or subtracted, the answer can contain no more decimal places than the least accurate measurement.
Significant Figures Adding and subtracting sig figs - your answer must be limited to the value with the greatest uncertainty.
Line up decimals and Add 150.0 g H2O (using significant figures) 0.507 g salt 150.5 g solution 150.5 g solution 150.0 is the least precise so the answer will have no more than one place to the right of the decimal.
Example Answer will have the same number of decimal places as the least precise measurement used. 12.11 cm 18.0 cm 1.013 cm 31.132 cm 9.62 cm 71.875 cm Correct answer would be 71.9 cm – the last sig fig is “8”, so you will round using only the first number to the right of the last significant digit which is “7”.
Significant Figures Multiplication and division of sig figs - your answer must be limited to the measurement with the least number of sig figs. 5.15 X 2.3 11.845 3 sig figs 2 sig figs only allowed 2 sig figs so 11.845 is rounded to 12 5 sig fig 2 sig figs
Multiplication and Division Answer will be rounded to the same number of significant figures as the component with the fewest number of significant figures. 4.56 cm x 1.4 cm = 6.38 cm2 = 6.4 cm2
28. 0 inches 2. 54 cm 1 inch Computed measurement is 71 28.0 inches 2.54 cm 1 inch Computed measurement is 71.12 cm Answer is 71.1 cm x = 71.12 cm
When both addition/subtraction and multiplication/division appear in the same problem In addition/subtraction the number of significant digits is limited by the value of greatest uncertainty. In multiplication/division, the number of significant digits is limited by the value with the fewest significant digits. Since the rules are different for each type of operation, when they both occur in the same problem, complete the first operation and establish the correct number of significant digits. Then proceed with the second and set the final answer according to the correct number of significant digits based on that operation
(1.245 + 6.34 + 8.179)/7.5 Add 1.245 + 6.34 + 8.179 = Then divide by 7.5 =
LET’S START WITH THE FIRST TOPIC SPEED
DESIGN YOUR OWN SPEED EXPERIMENT The owner of “Fast Buggy” toy car company has received numerous complaints that the motion of its “Super Speed Buggy” has been inconsistent and some cars are faster than others. As the quality control specialist, you are tasked with testing the cars to determine if the inconsistency claim is true or not. First you will need to set up a proposal as to how the cars will be tested.
ON YOUR OWN ON A SHEET OF LINED PAPER Define the problem: What are the variables you plan on testing? What are some controls that must be in place? What are some constraints/limitations you will have to work within to solve this problem? Plan the investigation: How will you set up the investigation? What kind of data should be collected? What tools will you need? How will these tools be used?
WRITING AND CONDUCTING THE EXPERIMENT With your groups use your brainstorming, write a procedure for testing and then conduct the experiment. Be sure to collect data to test your hypothesis. When analyzing your data how will you represent the data? Make sure you use your notes to help guide you.