Category: AP Physics 1

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2/3 AP: Momentum

photo showing cue ball breaking a triangle of billard balls

Momentum is a conserved property of a system. This conservation can be demonstrated by using Newton’s third law (Fa/b = -Fb/a) to develop the equation:

photo showing cue ball breaking a triangle of billard balls

mΔva + mΔvb = 0

Momentum is given the lowercase p as its symbol.

The change in momentum (Δp) of an object is defined as impulse.

Impulse = Δp = mΔv = FΔt

Keep in mind that while momentum depends on the same variables as kinetic energy (mass and velocity), momentum and kinetic energy are not the same thing. Momentum is always conserved, but, while energy is conserved, it can move from kinetic storage storage to gravitational, elastic, thermal, etc.

Today’s work

Some videos to help your understanding

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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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1/23-24 AP Phys: Energy practice problems in your textbook

Homework/classwork

Thursday

Page 152, Problems 21-24

Friday

Page 153, Problems 33, 35 (both spring energy), 47 (a red, make sure to do drawings before you start!), 29, 30, 32, 34, 43

Jackson suggests you do Problems 73 and 75; I guess I’ll have to try these this weekend 🙂

Questions? Post them below. Don’t forget, you can log in with just about any social network and receive email updates when your question is answered.

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1/23 AP Phys: Quantifying spring energy

Write the slope of your F/x calculations for each spring under the matching color on the whiteboard on the right.

Spring constants

As we saw yesterday, the relationship between the force applied to a spring and the stretch of the spring is linear. The slope of the F/ Δ x plot is

F = k* Δ x

which can be rearranged for the spring constant:

k=F/ Δ x

and the units of the spring constant must be N/m.

Review: Video showing the calculation of a spring constant

Similar to the lab we did in class, only this one uses the force of gravity between the earth and a hanging mass.

Calculating the energy in a spring

We demonstrated this both with algebra/geometry and with integrals in calculus. Vide of this will appear below soon.

Calculation video will appear here soon.

Flipping physics video.

Class/homework

In your textbook, Page 152, Problems 21-25. Complete tonight so we can whiteboard them tomorrow.

Problem 22: Here is a video of helper springs at work: https://youtu.be/GQs79EIw81M (this video is set to not allow embedding in other web sites. Below is another video that did allow embedding.

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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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01/15 Happy Martin Luther King, Jr. Birthday

Dr. ML King Jr. mugshot from 1963 Birmingham arrest
Dr. Kings “mug shot” from his arrest in 1963 in Birmingham, AL.

As we live through these sometimes difficult times, let us remember the amazing growth our nation has made.

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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.