Practical use of the coefficient of friction:
For 13 years I worked for a company that manufactured brake linings for cars and trucks. The friction between a brake pad and a brake rotor is what stops a vehicle. There were many engineers, mechanical, materials and chemical engineers, that worked in our lab developing different friction compounds for various vehicles. We also had a testing facility where mechanics would put a set of experimental pads on a vehicle, then accelerate to 60 mph and slam on the brakes. They would do this repeatedly while measuring stopping distances and the temperatures of the brake.
Thursday, December 6, 2018
Tuesday, December 4, 2018
Apologia Physics: Module 7 Sum of Vectors Lab
Sum of Vectors Lab
Module 7 covers various applications of Newton's Second Law. Force = mass x acceleration.
Calculations are straight forward when the forces are acting in a straight line. When forces are acting at angles, we have to separate the forces into the x and y directions (x and y axis on a graph). The above lab is a great demonstration.
I drew on the board a picture hanging from a nail. With one piece of wire attaching the picture to the nail, the tension on the wire has to be equal to the weight of the picture. If the picture is too heavy for the wire, the wire will break. One of the students asked if the picture could be hung with two nails and two pieces of wire. This would distribute the weight evenly and you could therefore use wire with less capacity as the weight on each nail is half the total weight of the picture.
It is when you use one nail and two attachments to the picture that the calculations get complicated. On an x and y axis graph, the wire now has tension in both directions. Therefore the forces on the wire is greater in total than just the weight of the picture because there is now horizontal force as well as vertical to take into account.
We will also do a lab to demonstrate the coefficient of friction of various materials.
Materials: one by four board a meter long, tape, aluminum foil, wax paper, sandpaper, box with weights.
Hypothesis: which material has the highest and lowest coefficient of friction?
Procedure: weigh the box with some weights inside. Weights can be coins, washers, etc. Use enough weight that the box slides when you raise the board. Apply one of the above (aluminum foil, wax paper, sandpaper) to the board, place the weighted box on the material being tested, raise the board and measure the height of the board when the box moves. Repeat three times. Then repeat with another surface. Using the height of the board, draw a picture of the board leaning at the height observed when the box moved, measure and calculate the angle of the board to the flat surface, then calculate the coefficient of friction. Note: you can measure the angle of the board with a protractor or by measuring the length of the board and the height at which the weight moved. The angle is the inverse sine of the height/length.
We also took the same board, placed a box weighted with a few quarters, and measured the coefficient of friction as above. Then we added weight to the box by adding another twenty quarters.
What do you think will happen? The resulting coefficient of friction was the same. Although the additional weight made the box more difficult to move in a horizontal direction, when the board was raised, there was more potential energy owing to the height of the board. Therefore, the box started to slide down the board at the same angle despite the additional weight in the box. The additional weight pushing down, the y coordinate, was offset by the additional force on the x coordinate.
To confirm this we put two boxes weighted as above, one lighter and one heavier, and ran them side by side on the same board. A good old American drag race! It was difficult to demonstrate that the boxes would move at the same time as we discovered various imperfections in the board. The box in the right lane of the board always moved last despite the different weights as there were some ridges in the wood. We then covered the wood in aluminum foil and got more consistent results.
Module 7 covers various applications of Newton's Second Law. Force = mass x acceleration.
Calculations are straight forward when the forces are acting in a straight line. When forces are acting at angles, we have to separate the forces into the x and y directions (x and y axis on a graph). The above lab is a great demonstration.
I drew on the board a picture hanging from a nail. With one piece of wire attaching the picture to the nail, the tension on the wire has to be equal to the weight of the picture. If the picture is too heavy for the wire, the wire will break. One of the students asked if the picture could be hung with two nails and two pieces of wire. This would distribute the weight evenly and you could therefore use wire with less capacity as the weight on each nail is half the total weight of the picture.
It is when you use one nail and two attachments to the picture that the calculations get complicated. On an x and y axis graph, the wire now has tension in both directions. Therefore the forces on the wire is greater in total than just the weight of the picture because there is now horizontal force as well as vertical to take into account.
We will also do a lab to demonstrate the coefficient of friction of various materials.
Materials: one by four board a meter long, tape, aluminum foil, wax paper, sandpaper, box with weights.
Hypothesis: which material has the highest and lowest coefficient of friction?
Procedure: weigh the box with some weights inside. Weights can be coins, washers, etc. Use enough weight that the box slides when you raise the board. Apply one of the above (aluminum foil, wax paper, sandpaper) to the board, place the weighted box on the material being tested, raise the board and measure the height of the board when the box moves. Repeat three times. Then repeat with another surface. Using the height of the board, draw a picture of the board leaning at the height observed when the box moved, measure and calculate the angle of the board to the flat surface, then calculate the coefficient of friction. Note: you can measure the angle of the board with a protractor or by measuring the length of the board and the height at which the weight moved. The angle is the inverse sine of the height/length.
We also took the same board, placed a box weighted with a few quarters, and measured the coefficient of friction as above. Then we added weight to the box by adding another twenty quarters.
What do you think will happen? The resulting coefficient of friction was the same. Although the additional weight made the box more difficult to move in a horizontal direction, when the board was raised, there was more potential energy owing to the height of the board. Therefore, the box started to slide down the board at the same angle despite the additional weight in the box. The additional weight pushing down, the y coordinate, was offset by the additional force on the x coordinate.
To confirm this we put two boxes weighted as above, one lighter and one heavier, and ran them side by side on the same board. A good old American drag race! It was difficult to demonstrate that the boxes would move at the same time as we discovered various imperfections in the board. The box in the right lane of the board always moved last despite the different weights as there were some ridges in the wood. We then covered the wood in aluminum foil and got more consistent results.
Tuesday, November 13, 2018
Apologia Physics: Newton's Laws
Even more Newtons
Discussed Newton's laws of motion. Did four easy demonstrations today to as examples. These are easy and fun to do.
1) Blow up a balloon then let go and measure how far the balloon flies. It is difficult to get the balloon to fly straight so do several iterations.
Then blow the balloon up to the same size, add some weight, then let if fly and measure how far it goes. For weight, attach some coins or popsicle sticks. Putting the weight inside the balloon seemed to work better.
2) Put and empty baby food jar or similar container upside down over another identical container. Put an index card between the two. Pull the card out fast enough that the top jar remains on the bottom jar.
3) Put an index card on top of a baby food jar and put a large washer or a quarter in the center of the card. Pull the card out quickly. If you do it fast enough the quarter drops to the bottom of the jar.
4) Stack up at least six or seven quarters or large washers. Sharply hit the bottom quarter with a plastic ruler. The bottom one or two quarters will go flying off but the remainder of the stack should just drop down with out scattering.
Which laws are being demonstrated here?
Each student is required to write a lab report on one of the above demos. Each report should include:
Student's name
Date
Title of lab
Purpose of lab
Hypothesis
List of materials
Outcome of the lab
Discussion of results-what went right, what went wrong, what could be done to improve results
What you learned
Sections of the report should be written in paragraphs with proper punctuation, grammar, spelling, etc. The English Comp lesson comes free with the Physics class!
Write in the third person, present tense, and active voice.
Here are a few photos.
Discussed Newton's laws of motion. Did four easy demonstrations today to as examples. These are easy and fun to do.
1) Blow up a balloon then let go and measure how far the balloon flies. It is difficult to get the balloon to fly straight so do several iterations.
Then blow the balloon up to the same size, add some weight, then let if fly and measure how far it goes. For weight, attach some coins or popsicle sticks. Putting the weight inside the balloon seemed to work better.
2) Put and empty baby food jar or similar container upside down over another identical container. Put an index card between the two. Pull the card out fast enough that the top jar remains on the bottom jar.
3) Put an index card on top of a baby food jar and put a large washer or a quarter in the center of the card. Pull the card out quickly. If you do it fast enough the quarter drops to the bottom of the jar.
4) Stack up at least six or seven quarters or large washers. Sharply hit the bottom quarter with a plastic ruler. The bottom one or two quarters will go flying off but the remainder of the stack should just drop down with out scattering.
Which laws are being demonstrated here?
Each student is required to write a lab report on one of the above demos. Each report should include:
Student's name
Date
Title of lab
Purpose of lab
Hypothesis
List of materials
Outcome of the lab
Discussion of results-what went right, what went wrong, what could be done to improve results
What you learned
Sections of the report should be written in paragraphs with proper punctuation, grammar, spelling, etc. The English Comp lesson comes free with the Physics class!
Write in the third person, present tense, and active voice.
Here are a few photos.
Thursday, November 8, 2018
Steps to Write a Lab Report (Mrs. Stevens' guide)
Last week, we did another lab, Elephant’s Toothpaste. Now, the class should learn how to write a report and draw conclusions. Lab design, creating hypotheses, and drawing conclusions are tedious to teach. Here is the lab rubric I use for Chemistry. Last week Elephant’s Toothpaste uses hydrogen peroxide, yeast, and dish soap. The kids varied the number of grams of yeast and timed the soapy solution as it reached the top of the test tube. Here goes the lesson.
1. What is the hypothesis? A hypothesis has two parts: null and alternate
a. The null hypothesis for this lab is, “There is no relationship between the number of grams of yeast and the time it takes for the soapy solution to reach the top of the test tube—or The time of reaction is independent of the amount of yeast.”
b. The alternate or alternative hypothesis (your best guess) is, “The more grams of yeast, the shorter the time for the soapy solution to reach the top of the test tube—or The more yeast, the faster the reaction.”
2. The next section is background material. Yeast contains the enzyme, catalase, in the cell’s peroxisome organelles. Hydrogen peroxide is a common waste product in cells. (Waste is bad.). The catalase breaks down hydrogen peroxide. In this lab, the yeast is allowed to bloom and produce catalase, which breaks down hydrogen peroxide. Kids can write the background in quotes—but must cite the source.
3. Next is the chemical reaction for this experiment., if pertinent. Hydrogen peroxide breaks down in the presence of catalase into water and oxygen. Students may write the balanced reaction neatly in pen or 2 H2O2 —— H2O + O2
4. On to the materials. The materials include the following items: test tube rack, six test tubes, a test tube holder, scoopula, one disposable, graduated, transfer pipette, a 50 mL graduated cylinder, a 10
mL graduated cylinder, cell phone stop watch, three plastic beakers, one digital thermometer, a tray or trough for overflow, a digital scale, one weigh boat, 20 grams of yeast, 30 mL dish soap, 200 mL water, and one craft stir stick. Note the grammar! Numbers ten or fewer are spelled and greater are written in Arabic character, one and 50. Please note a colon follows a noun. The sentence above is an example of the use of third person, present tense, active voice, and indicative mood.
5. The next section, results, includes the data, ideally a table or chart. The student may write the results. For example, the results are five grams of yeast produces suds in 4.9 seconds.
6. The procedures must be discussed step by step. The controlled variables are the water temperature, the amount of water, dish soap, and hydrogen peroxide. The independent variable is the number of grams of yeast. The student completes three trials. For each trial, the student adds one milliliter of yeast solution to one milliliter of dish soap and five milliliters of hydrogen peroxide in a 25 mL test tube. The student measures each trial with a stopwatch to assess the time the soapy solution travels to the top of the test tube. The student records each trial in a table.
7. The discussion section follows the data. This section has any observations or mistakes. The student notes that 25 grams of yeast causes an eruption of suds to quick to measure. This is the point
the student determines if the results support or refute the null or alternate hypotheses. It is not
unusual for the results to refute both. Here, the child should use the Claim Evidence Reasoning approach to describe the results. The claim is that more yeast results in a faster reaction. The student’s data table should indicate shorter intervals. The reasoning is that more yeast produces more catalase, consequently breaks down more hydrogen peroxide.
8. Lastly is the conclusion. My standard conclusion is this one, “More trials are indicated.” “More study is needed to determine the results support the alternate hypothesis.”
1. What is the hypothesis? A hypothesis has two parts: null and alternate
a. The null hypothesis for this lab is, “There is no relationship between the number of grams of yeast and the time it takes for the soapy solution to reach the top of the test tube—or The time of reaction is independent of the amount of yeast.”
b. The alternate or alternative hypothesis (your best guess) is, “The more grams of yeast, the shorter the time for the soapy solution to reach the top of the test tube—or The more yeast, the faster the reaction.”
2. The next section is background material. Yeast contains the enzyme, catalase, in the cell’s peroxisome organelles. Hydrogen peroxide is a common waste product in cells. (Waste is bad.). The catalase breaks down hydrogen peroxide. In this lab, the yeast is allowed to bloom and produce catalase, which breaks down hydrogen peroxide. Kids can write the background in quotes—but must cite the source.
3. Next is the chemical reaction for this experiment., if pertinent. Hydrogen peroxide breaks down in the presence of catalase into water and oxygen. Students may write the balanced reaction neatly in pen or 2 H2O2 —— H2O + O2
4. On to the materials. The materials include the following items: test tube rack, six test tubes, a test tube holder, scoopula, one disposable, graduated, transfer pipette, a 50 mL graduated cylinder, a 10
mL graduated cylinder, cell phone stop watch, three plastic beakers, one digital thermometer, a tray or trough for overflow, a digital scale, one weigh boat, 20 grams of yeast, 30 mL dish soap, 200 mL water, and one craft stir stick. Note the grammar! Numbers ten or fewer are spelled and greater are written in Arabic character, one and 50. Please note a colon follows a noun. The sentence above is an example of the use of third person, present tense, active voice, and indicative mood.
5. The next section, results, includes the data, ideally a table or chart. The student may write the results. For example, the results are five grams of yeast produces suds in 4.9 seconds.
6. The procedures must be discussed step by step. The controlled variables are the water temperature, the amount of water, dish soap, and hydrogen peroxide. The independent variable is the number of grams of yeast. The student completes three trials. For each trial, the student adds one milliliter of yeast solution to one milliliter of dish soap and five milliliters of hydrogen peroxide in a 25 mL test tube. The student measures each trial with a stopwatch to assess the time the soapy solution travels to the top of the test tube. The student records each trial in a table.
7. The discussion section follows the data. This section has any observations or mistakes. The student notes that 25 grams of yeast causes an eruption of suds to quick to measure. This is the point
the student determines if the results support or refute the null or alternate hypotheses. It is not
unusual for the results to refute both. Here, the child should use the Claim Evidence Reasoning approach to describe the results. The claim is that more yeast results in a faster reaction. The student’s data table should indicate shorter intervals. The reasoning is that more yeast produces more catalase, consequently breaks down more hydrogen peroxide.
8. Lastly is the conclusion. My standard conclusion is this one, “More trials are indicated.” “More study is needed to determine the results support the alternate hypothesis.”
Apologia Physics Two Dimensional Motion Conclusion
Summarized main points of parabolic motion and discovered a few things:
When a projectile is fired or thrown near the surface of the earth its path is parabolic. Several students debated the pronunciation of the noun, parabola, and the adjective, parabolic.
The x and y components of a projectile's motion can be treated as two separate one-dimensional situations. The x component's velocity does not change once the projectile has been launched. The y component is gravity.
A projectile's maximum height will be reached when the y component of its velocity is zero.
If the projectile lands at the same height from which it was launched, it will reach its maximum height at the midpoint of the journey. The final value of Vy will be the negative of the initial value of Vy. In other words, the final velocity equals the initial velocity. Good examples are throwing a football to anther person, firing a cannon at a target.
To show that the y component velocity is independent of the x component we timed how long it took a rubber band to hit the floor after being shot a few feet as shown below and also by just dropping it from the same height. Two groups had times within a ten percent error, very good, and one group was repeatedly off by 30% I should have had them change timers!
In calculations remember that the Cosine of zero is 1 (one) and the Sine of zero is zero.
We looked at the range formula. Range = V^2 (initial velocity) times sin2times the angle divided by gravity. It is not important to be able to derive this formula although the derivation is in the book. You would use this formula to determine how far a projectile would fly based on initial velocity and the angle from the ground.
We made several observations from the range formula. If you double the initial velocity, the range is quadrupled as V is squared in the range equation. If you were aiming at a target and your first shot fell short, you would decrease the angle to get the projectile to go farther. Handy to know if you are firing a mortar or throwing a football.
When a projectile is fired or thrown near the surface of the earth its path is parabolic. Several students debated the pronunciation of the noun, parabola, and the adjective, parabolic.
The x and y components of a projectile's motion can be treated as two separate one-dimensional situations. The x component's velocity does not change once the projectile has been launched. The y component is gravity.
A projectile's maximum height will be reached when the y component of its velocity is zero.
If the projectile lands at the same height from which it was launched, it will reach its maximum height at the midpoint of the journey. The final value of Vy will be the negative of the initial value of Vy. In other words, the final velocity equals the initial velocity. Good examples are throwing a football to anther person, firing a cannon at a target.
To show that the y component velocity is independent of the x component we timed how long it took a rubber band to hit the floor after being shot a few feet as shown below and also by just dropping it from the same height. Two groups had times within a ten percent error, very good, and one group was repeatedly off by 30% I should have had them change timers!
In calculations remember that the Cosine of zero is 1 (one) and the Sine of zero is zero.
We looked at the range formula. Range = V^2 (initial velocity) times sin2times the angle divided by gravity. It is not important to be able to derive this formula although the derivation is in the book. You would use this formula to determine how far a projectile would fly based on initial velocity and the angle from the ground.
We made several observations from the range formula. If you double the initial velocity, the range is quadrupled as V is squared in the range equation. If you were aiming at a target and your first shot fell short, you would decrease the angle to get the projectile to go farther. Handy to know if you are firing a mortar or throwing a football.
Tuesday, October 30, 2018
Module Four Summary and begin Popsicle stick catapult lab
Wrapped up module four with test of problems concerning the addition of vectors.
The main take-away from vector addition:
If they ask to add two vectors, you have to get the x and y components of each vector and add together. Then use the Pythagorean theorem to solve for the magnitude. Then use the inverse tangent to get the angle. If they give you one vector and ask for the x and y components you take the sine and cosine of the angle times the magnitude.
We made catapults. Our plan is to use these math calculations next week to analyze parabolic
motion.
Today we used out catapults to shoot marshmallows. We measured the height and length of the motion. We measured the time elapsed from launch to landing. We measured the angle of the launch with a protractor. I challenged the students to calculate the exit speed of the marshmallow. Several had the idea to use x = Vinitial x time plus 1/2 at^2. There are several other calculations required before this equation can be used. They will have to follow the Dr. Math equations referred to in the previous paragraph.
Several students had difficulty getting consistent trajectories or had launches that went straight up. We had to experiment with placement of the fulcrum, attachment points of the lever, and the attachment of the spoon to the stick. Do not bend the spoon; that interferes with the measurement of the lever and the launch angle. When we were making the catapults I said to use only rubber bands and not tape. Those who used tape had difficulty making the adjustments needed to fix the trajectory of their launch.
The main take-away from vector addition:
If they ask to add two vectors, you have to get the x and y components of each vector and add together. Then use the Pythagorean theorem to solve for the magnitude. Then use the inverse tangent to get the angle. If they give you one vector and ask for the x and y components you take the sine and cosine of the angle times the magnitude.
We made catapults. Our plan is to use these math calculations next week to analyze parabolic
motion.
Today we used out catapults to shoot marshmallows. We measured the height and length of the motion. We measured the time elapsed from launch to landing. We measured the angle of the launch with a protractor. I challenged the students to calculate the exit speed of the marshmallow. Several had the idea to use x = Vinitial x time plus 1/2 at^2. There are several other calculations required before this equation can be used. They will have to follow the Dr. Math equations referred to in the previous paragraph.
Several students had difficulty getting consistent trajectories or had launches that went straight up. We had to experiment with placement of the fulcrum, attachment points of the lever, and the attachment of the spoon to the stick. Do not bend the spoon; that interferes with the measurement of the lever and the launch angle. When we were making the catapults I said to use only rubber bands and not tape. Those who used tape had difficulty making the adjustments needed to fix the trajectory of their launch.
Friday, October 19, 2018
Two Dimensional Motion
Motion can have two forces. For example, the current of a river acting upon the direction of a boat or the cross winds that impact the direction of an airplane. To understand the net impact of two forces on an object we have to use basic trigonometry. We reviewed the basic types of triangles: Scalene, Isoceleses, Equalateral, Obtuse and Right. We reviewed that the sum of the angles in a triangle is 180 degrees. We reviewed the difference between Radians and Degrees. There are two times Pi radians in a circle. This is important to understand because we will be using TI83 & 84 calculators and also Excel to calculate Sine, Cosine and Tangent. One has to check the Mode in the calculators to ensure you are using Degrees and not Radians. In Excel you have to convert degrees to radians before performing the calculations. I introduced the students to SAHCOHTOA, an anagram for the basic trigonometric equations.
SAH sine = adjacent over hypotenuse
COH cosine = opposite over hypotenuse
TOA tangent = opposite over adjacent
For practice, we measured the height of the library roof. Each student stood back from the library wall at least 6 to 10 meters. Then we used a protractor to measure the angle from where the student was situated to the top of the roof. We therefore had the angle and the adjacent side of a right triangle. To determine the height of the roof, which is the height of the library wall and is the opposite side of the triangle, we used the tangent calculation.
Motion can have two forces. For example, the current of a river acting upon the direction of a boat or the cross winds that impact the direction of an airplane. To understand the net impact of two forces on an object we have to use basic trigonometry. We reviewed the basic types of triangles: Scalene, Isoceleses, Equalateral, Obtuse and Right. We reviewed that the sum of the angles in a triangle is 180 degrees. We reviewed the difference between Radians and Degrees. There are two times Pi radians in a circle. This is important to understand because we will be using TI83 & 84 calculators and also Excel to calculate Sine, Cosine and Tangent. One has to check the Mode in the calculators to ensure you are using Degrees and not Radians. In Excel you have to convert degrees to radians before performing the calculations. I introduced the students to SAHCOHTOA, an anagram for the basic trigonometric equations.
SAH sine = adjacent over hypotenuse
COH cosine = opposite over hypotenuse
TOA tangent = opposite over adjacent
For practice, we measured the height of the library roof. Each student stood back from the library wall at least 6 to 10 meters. Then we used a protractor to measure the angle from where the student was situated to the top of the roof. We therefore had the angle and the adjacent side of a right triangle. To determine the height of the roof, which is the height of the library wall and is the opposite side of the triangle, we used the tangent calculation.
Thursday, October 11, 2018
Apologia Physics: Motion in one direction
Using formulas to solve for Velocity, Distance, Acceleration, and Time
It is important to remember one key rule of algebra: order of operations, inside parenthesis and outside. For example in the equation x = 1/2 at^2 be sure to square the number and the units of measure that are represented by t. It is also helpful to write fractions (and the accompanying units of measure) with the numerator on top of a line and the denominator below the line. This is obvious but if you use a slash as in the way I wrote one-half above, it can be confusing to eliminate the units of measure.
Several students were showing a shortfall in their knowledge of algebra and scientific notation so I sent them links to Khan Academy's Algebra Basics . Dr. Khan does a great job explaining anything mathematical. I've used this site to refresh my memory on how to use sine, cosine, and tangent which we will be using soon in our calculations.
We have several students who would rather not use scientific notation but write out the number. This is okay for small calculations and numbers but will be a major problem when using larger numbers and more complicated equations. I told the class that if anyone has an aversion to the use of scientific notation they should immediately expunge this thought from their brain!
It is important to remember one key rule of algebra: order of operations, inside parenthesis and outside. For example in the equation x = 1/2 at^2 be sure to square the number and the units of measure that are represented by t. It is also helpful to write fractions (and the accompanying units of measure) with the numerator on top of a line and the denominator below the line. This is obvious but if you use a slash as in the way I wrote one-half above, it can be confusing to eliminate the units of measure.
Several students were showing a shortfall in their knowledge of algebra and scientific notation so I sent them links to Khan Academy's Algebra Basics . Dr. Khan does a great job explaining anything mathematical. I've used this site to refresh my memory on how to use sine, cosine, and tangent which we will be using soon in our calculations.
We have several students who would rather not use scientific notation but write out the number. This is okay for small calculations and numbers but will be a major problem when using larger numbers and more complicated equations. I told the class that if anyone has an aversion to the use of scientific notation they should immediately expunge this thought from their brain!
Thursday, October 4, 2018
Measuring displacement using time and acceleration of gravity
This week we have been reviewing the five basic formulas for One-Dimensional Motion and Free Fall.
First lab was to measure the time it took for several objects to fall from a measured height. We discussed what factors we could control such as using the same person to do the drop and the same person to do the timing. We used the formula x=1/2*a*t2 to determine if we had measured the time accurately as we knew the displacement (x) and the acceleration of gravity (a). We calculated the margin of error in our time measurements.
We also had a lesson in solving (using Solver in TI 84) this type of equation on the Texas Instruments graphing calculator. We have several used graphing calculators. A good graphing calculator app for ipad (Search for TI84) is about $10, much less than a graphing calculator. A used TI 83 or 84 is maybe $25. Don't buy an 86 or 89. It would be very useful if you purchased either a calculator or the app as we will be performing many of the same calculations and also need a way to look up sine, cosine and tangent later in the course.
Second lab was using a tennis ball and stopwatch to measure the height of the library roof where we meet. Again, using the formula above we measured the time for the ball to drop from the roof to the sidewalk. We were not able to climb on the roof so we thru the ball in the air so that it reached the level of the roof then timed the drop to the sidewalk. With our measurement of time (t) and the acceleration of gravity (a) we measured the height of the roof. We were able to verify this by counting the number of panels in the wall of the building and multiplying by the height of a panel.
First lab was to measure the time it took for several objects to fall from a measured height. We discussed what factors we could control such as using the same person to do the drop and the same person to do the timing. We used the formula x=1/2*a*t2 to determine if we had measured the time accurately as we knew the displacement (x) and the acceleration of gravity (a). We calculated the margin of error in our time measurements.
We also had a lesson in solving (using Solver in TI 84) this type of equation on the Texas Instruments graphing calculator. We have several used graphing calculators. A good graphing calculator app for ipad (Search for TI84) is about $10, much less than a graphing calculator. A used TI 83 or 84 is maybe $25. Don't buy an 86 or 89. It would be very useful if you purchased either a calculator or the app as we will be performing many of the same calculations and also need a way to look up sine, cosine and tangent later in the course.
Second lab was using a tennis ball and stopwatch to measure the height of the library roof where we meet. Again, using the formula above we measured the time for the ball to drop from the roof to the sidewalk. We were not able to climb on the roof so we thru the ball in the air so that it reached the level of the roof then timed the drop to the sidewalk. With our measurement of time (t) and the acceleration of gravity (a) we measured the height of the roof. We were able to verify this by counting the number of panels in the wall of the building and multiplying by the height of a panel.
Thursday, September 27, 2018
Apologia Physics: Motion
The Physics class uses Apologia Physics. (NOT Physical Science.) We meet twice a week.
Week One:
1. Pre-Assessment for Physics
2. Accuracy and Precision Activity
3. Density Series of Activities
4. How to Graph
Once, we complete these preliminary exercises, we'll start Module 1.
Module 1
Metric Measures
Module 2
Excel for Physics
Motion Overview Powerpoint
Our class is following the Apologia Physics textbook. (Either edition is fine.) We did start with a unit on measures. I had the kids measure a variety of objects: marbles, metal cubes, water with a graduated cylinder, etc. The kids measured with calipers, rulers, digital scale, and density by displacement. (This lab is similar.) During this unit, we covered measures, metrics, percent error, precision, accuracy, significant figures, and working with exponents. I wanted the kids to demonstrate basic lab skills, such as using a weigh boat with a digital scale.
The next lab was with motion. We wanted to measure speed. We used simple wooden ramps and Hot Wheels ramps with balls and small cars. I gave the kids Go Pro with Hot Wheels (which connects with an iPad) and two meters of Hot Wheels track to determine speed. The kids measured both the time the car took to cover the track and the distance of the track. To determine the speed, we used the number of frames on the GoPro video to travel a certain distance. The lab became an inquiry activity. (FYI, Lowes cut meter length boards we use as ramps.) The goal was to understand how to measure speed.
The third unit is Excel. The class needs to know how to use Excel (or Google Sheets) before college. The Excel for Physics was our guide. The kids entered and graphed data for speed and acceleration. Using this data the class produced a graph and performed calculations of speed and acceleration. It is important to be able to write formulas that refer to the cell references to perform calculations and not use actual numbers. I discovered I needed to help most students one at a time with the concept of writing formulas using cell references and proper algebra (order of operations, use of parentheses, etc.) It is important that students use Excel to organize data and perform calculations without first writing the same information on paper. We also learned to interpret graphs using the slope of the line to determine where a subject was accelerating, decelerating, holding a steady speed, and turning around.
Week One:
1. Pre-Assessment for Physics
2. Accuracy and Precision Activity
3. Density Series of Activities
4. How to Graph
Once, we complete these preliminary exercises, we'll start Module 1.
Module 1
Metric Measures
Module 2
Excel for Physics
Motion Overview Powerpoint
Our class is following the Apologia Physics textbook. (Either edition is fine.) We did start with a unit on measures. I had the kids measure a variety of objects: marbles, metal cubes, water with a graduated cylinder, etc. The kids measured with calipers, rulers, digital scale, and density by displacement. (This lab is similar.) During this unit, we covered measures, metrics, percent error, precision, accuracy, significant figures, and working with exponents. I wanted the kids to demonstrate basic lab skills, such as using a weigh boat with a digital scale.
The next lab was with motion. We wanted to measure speed. We used simple wooden ramps and Hot Wheels ramps with balls and small cars. I gave the kids Go Pro with Hot Wheels (which connects with an iPad) and two meters of Hot Wheels track to determine speed. The kids measured both the time the car took to cover the track and the distance of the track. To determine the speed, we used the number of frames on the GoPro video to travel a certain distance. The lab became an inquiry activity. (FYI, Lowes cut meter length boards we use as ramps.) The goal was to understand how to measure speed.
The third unit is Excel. The class needs to know how to use Excel (or Google Sheets) before college. The Excel for Physics was our guide. The kids entered and graphed data for speed and acceleration. Using this data the class produced a graph and performed calculations of speed and acceleration. It is important to be able to write formulas that refer to the cell references to perform calculations and not use actual numbers. I discovered I needed to help most students one at a time with the concept of writing formulas using cell references and proper algebra (order of operations, use of parentheses, etc.) It is important that students use Excel to organize data and perform calculations without first writing the same information on paper. We also learned to interpret graphs using the slope of the line to determine where a subject was accelerating, decelerating, holding a steady speed, and turning around.
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