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5/15 PitU: This week: Climate and physics

Image showing water temperatures in the northern Pacific ocean on Aug 27, 2013

Acid and the ocean

The average pH of the ocean is 8.1, which means it is on the base side of the pH scale (remember, less than 7 is acidic, greater than 7 is basic). When scientists talk about ocean acidification, they are actually talking about ocean ‘de-basicifiction’—but that doesn’t sound as good 🙂

Ocean acidification

An unusual type of acid is carbon dioxide (CO2). It’s unusual because most acids have a hydrogen atom/ion on them somewhere that can dissociate when the acid is mixed with water. Here’s the process that carbon dioxide undergoes when mixed with water:

How carbonic acid effects shells in the ocean

Watch the following video. It is part a review of acid/bases and pH, and part an introduction to oceans turning a bit more acidic.

Remember: pH 7 is neutral, greater than 7 is basic, lower than 7 is acidic.

Reading & questions

Read the article here.

Questions

  1. What is pH and how is it measured?
  2. How is ocean acidification related to a global increase in temperature?
  3. What is the Kyoto Protocol? 
  4. What chemical reaction happens when CO2 and seawater (H2O) mix?
  5. Explain how shelled organisms are negatively impacted by ocean acidification.
  6. What are a few ways you can help reduce global ocean acidification?

Submit photo of answers

Submit a photo of your answers here. If you use more than one page, it’s OK to only submit the first page.

Further reading/viewing

If you’d like more information on this topic, here are some resources:

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2/10 PotU: More energy

image showing three energy bar charts and a system box

Hi all. I’m out for another day or two (extreme sore throat, no, not caronavirus!)

Warm up

Draw an energy bar chart set for the mousetrap car as it goes from (1) fully wound up to (2) moving across the floor and finally (3) stopped on the floor.

image showing three energy bar charts and a system box

Today you will have a reading and worksheet to practice on energy and working. Hopefully I’ll be back tomorrow so we can start on the mousetrap cars.

If you do not complete today’s assignment in class (it’s a shorter day), please complete it for homework.

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1/28: AP Phys: Power

In our study of energy and work, we have yet to address the time it takes to transfer energy from one system to another. This rate is called power, and given symbol P (upper case, we’ll use the lower-case p for another variable later). Since the rate is time based, the equation for power is:

P = Δ E/ Δ t

The units for power from this equation would be J/s, which physicists shortened to Watt, with the symbol W (upper-case since it’s named after a person, James Watt). So…

1 J / s = 1 W

Class practice

Work your way through Problem 5.12 on Page 143.

Class and homework

Page 154, problems 48, 50, 51, 53, 54

Book resources

Section 5.6: Power, pages 142-146

Some power trivia

  • The most powerful production car (not specially built or modified) is the Bugatti’s 8.0-litre W16 in the Chiron. Four turbos help this car mill 1,479hp (1.2MW) through its 8.0-litre quad-turbo W16 engine, producing a massive 187.5 horsepower per liter. It’s mass is 2,000 kg.
  • The most powerful pickup truck is the 2019 Ford Super Duty (F250 and F350). Ford’s 6.7-liter diesel V8 delivers 450 horsepower (336 kW); more than any other truck in this class. The mass of this truck is 3,500 kg.
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1/22 AP Phys: Energy in springs: Hooke’s Law and Spring constants

Goals

  • Analyze the relationship between how far a spring is stretched (Δx) and the force required to hold it at that distance.
  • Develop a model for energy in a spring based on (ΣE) + W = (ΣE)
    • If the spring has no initial energy, then the work done on the spring equals the final elastic/spring energy.

Procedures, general outline

You will need to think about how you are making the following measurements, and record the details of your procedures in your lab book.

Photo of four tubular spring scales
  1. Before you start, read the procedures and create a data table with all the necessary columns and rows.
  2. Chose a tubular spring scale from the bin, and records its color.
  3. Pull a spring scale out and hold it at any distance.
  4. Record the stretch (Δx) of the spring.
  5. Record the force measurement of the scale.
  6. Repeat at several different lengths, until you are comfortable that you can plot the data and be confident that your choice of linear or exponential fit is an accurate model.
  7. Repeat steps 2-6 for a total of three different colored spring scales.

Analysis

  • Analyze your data using a scatter plot, and develop an equation for each spring.
    • Plot stretch as the independent variable.

Conclusion development

  • Develop conclusions with your group about the relationship.
  • Prepare to present a whiteboard tomorrow: You should have a small box in your lab book showing what you will write on your whiteboard tomorrow.

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01/17 PotU: Sound, energy, and music

Warm up

Copy and complete the following sentence by selecting one of the bold words:

In musical instruments, low notes are created by making the string or tube longer or shorter, or by making it thicker or thinner.

Today’s videos

What is sound?

How does sound travel

Highlights from videos

What is sound

image of complex sound wave
image of a sound wave composed of many different waves combined
  • Compression: Areas where atoms/molecules are squeezed closer together (have more elastic energy).
  • Rarefaction: Areas where molecules are spread apart (have less elastic energy).
  • Hz (short for Hertz, like the rental car company) is a measure of the frequency: 1 cycle every second = 1 Hz. An example in sound: 440 Hz is the note “A.”
  • The medium is the substance the waves travel through. The medium moves only a short distance; it’s the energy that moves the entire distance from the source of the wave to whatever receives that energy (e.g. from a speaker to your ear).

How does sound travel

This video starts with a thought experiment. Thought experiments are experiments we can’t actually do, but by thinking about that situation, it helps us to understand. By looking at a super-long bar of metal, we can ‘slow down’ sound.

  • Wave motion can be thought of as a chain reaction of one portion moving the portion next to it.
  • Sound waves are particles bouncing into each other
  • Particles only travel a short distance
  • Speed of sound depends on the material the medium is made up of.
  • Sound waves are not objects, they are the movement of energy.
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01/16 PotU: Sound energy

Notes from today

Image of inner ear.
The cochlea contains the nerves that resonate at different sound frequencies (notes).
  • Metronome: A device that keeps the rhythm; aka the “beat”
  • The shorter something is, the faster it vibrates.
    • We had a demonstration of the vibrating bar from the fall final; the shorter the bar was, the faster it vibrated.
  • Both string and wind instruments depend on lengthening or shortening the material that the sound is produced by to create different notes.
    • In some cases, the string is thicker (lower notes) or thinner (lower notes).
  • Our ears have hearing nerves: The long ones detect low notes, and the short ones high notes.
    • As we get older, our short cells tend to die off more than our long ones, so kids and teenagers can often hear sounds that adults can’t
    • A dog whistle is similar: The frequency is so high that people can’t hear it, but dogs can.

Sound is the rhythmic motion of air particles. So, similar to thermal energy, it is a type of kinetic energy.

Humans are said to be able to hear from 20 to 20,000 Hz (cycles per second). Test your hearing range with the video below. (I can hear from about 60 to 13,000 Hz.)

When the ball hits the tuning fork:

  • Kinetic (ball moving towards tuning fork) moves from the ball into
  • Sound energy from the tuning fork.

The video below shows a tuning fork being lowered into a glass of water, shot with a very high speed cameras (about 50 times faster than most cell phone cameras, and even faster than the slow-mo option on phone cameras).

Sample instruments

In the instruments below, notice how the length and/or thickness changes to make a range of notes.

Piano

Image of strings in a grand piano
Notice the long, thick strings on the left side (top in this photo) for the lower notes, and the short, thinner strings on the right (bottom in this photo).
The longer strings are placed above the shorter ones for space efficiency.

Trombone

Navy band trombone setcion
Trombones have a section that can slide in and out to make the tube length longer or shorter.

Clarinet

Two clarinets
Clarinet players place their fingers over the wholes in the instrument to make the effective tube length shorter. The lowest note is will all wholes covered.
Flutes and recorders use a similar system.

Percussion instruments

Percussion instruments
Percussion instruments come in all shapes and sizes. The larger ones generally produce lower notes.

Ukulele

Soprano ukulele
The ukulele has two thick strings in the middle, and outside strings are thinner.
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1/15 AP Phys: Conservation of energy with springs & ramps

Learning objectives

The student is able to describe and make qualitative and/or quantitative predictions about everyday examples of systems with internal potential energy. (Science Practices 2.2, 6.4, and 7.2)

Introduction

Observe the demonstration and take notes on your observations and questions. Think about/answer the following questions:

  • If the track were steeper or shallower, how would the motion change? Justify your answer using your knowledge of kinematics and energy.
  • Short answer on our own (2 minutes).
  • Expand answer with our group (3 minutes) .
  • Expand answer with the class (5 minutes) .

Equipment

  • Low friction cart
  • Ramp
  • Meterstick
  • Stopwatch
  • Assorted masses

Tools

photo of a clinometer on a sloped surface displaying angle in degrees.
Clinometer measures the angle of a slope.
  • Calculator
  • Clinometer to measure angle of ramp
  • Whiteboard for sharing group work
  • Books or other objects to change the steepness of the track

Safety

  • Please keep carts on tables to prevent people from slipping on them (or damaging them).
  • The carts have spring plungers; make sure they aren’t compressed near delicate parts of your body, or breakable objects.
  • Think and be careful

Design and conduct an experiment to answer the following question.

  • If the track were steeper or shallower, how would the motion change? Justify your answer using your knowledge of kinematics and energy.

Keep focused on your objective!

Provide detailed procedural steps. Make sure that if you gave them to someone who had not completed the lab, they could do everything completely and in the same way your group did it.

Why are you doing each step, and what are reasonable measurements.

Are you completing these steps as you progress?

  1. Prelab notes
  2. Title
  3. Purpose
  4. Personal procedures/ideas
    • Group procedures/ideas/notes
  5. Class procedures/ideas/notes
  6. Data table
  7. Notes on experiment from as you conduct it.
  8. Scatter plot or other visual analysis of data.
  9. Processing/analyzing data:
  10. Group conclusion (what can your group conclude, without looking at other groups’ data?)
  11. Whiteboard notes
  12. Class data comparison and conclusions.

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01/8-13 AP Physic: Energy

Wednesday & Thursday, Jan 8 & 9

We added energy equations and the work work/energy theorem to our energy knowledge. In physics, work is used to add or remove energy from a system.

Class/homework: Page 151, # 9-18

Friday, Jan 10

We worked on an energy simulation using the PhET Energy Skate Park simulation. You can see the assignment here, and the simulation here:

Monday, Jan 13

We started learning about power. Textbook Section 5.6, pages are 142-146. Solve problems 48-54 on page 154.