Author: Lee Trampleasure

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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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1/30 PotU: Waves math

Image of a wave showing wavelength, distance and amplitude

From the Waves on a String packet, we were able to develop the wave equation:

speed = wavelength x frequency

or, using symbols:

s = λ x f

Units for each variable are:

  • speed in m/s
  • wavelength in meters
  • frequency in Hz (‘Hertz’)

Measurements of a wave are shown below.

Image of a wave showing wavelength, distance and amplitude
Wave properties and how to measure them.

Today’s practice worksheet

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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.