Work-Energy Theorem this week in Physical Science

Wednesday will be our last day for new material in Physical Science, and we will spend the next three days wrapping up our discussion of work and energy, with focus on the Work-Energy theorem. This will give the students a powerful tool to analyze kinematic systems, and indeed most advanced studies of mechanics focus not on the traditional equations of motion (which, altho valid, prove cumbersome for complex systems) but on the conservation of energy within the system.

For 10 points of extra credit, students can answer the following question:

Last week in class we wrote two formulas relating the height an object falls from and the time it takes to fall. Use a similar approach to write a formula for the work done by gravity on an object with mass m moved with vertical displacement h.

This extra credit is due tomorrow (Monday).


Finishing gravity, starting energy, work, and power this week in Physical Science

This week in Physical science we will be finishing our discussion of gravity, then moving on to the topics of energy, work, and power. In common usage energy and power are often used to mean the same thing, but in science they mean two separate but related ideas: power is simply the amount of energy per unit time. This leads to a somewhat convoluted measure of energy on your electric bill, the kilowatt-hour, which is energy per unit time multiplied by time, thus leaving energy. Work in a physics sense is perhaps the most confusing concept to grasp, since one can exert a great amount of effort but do no work: for example, carrying a heavy box across a room does no work if analyzed at a basic level of physics.

For ten points of extra credit, students can answer the following question and turn it in by Wednesday:

Who is the unit of energy named after, and when was he alive?

Action-Reaction Force Pairs this Week in Physical Science

This week in physical science we will be discussing action-reaction force pairs, so famously summarized by one form of Newton’s Third Law: For every action there is an equal and opposite reaction. In physics we describe this it a little more precisely: For every force, there is a corresponding reaction force equal in magnitude and opposite in direction. This phenomenon is readily apparent in the “kick” of a firearm, the force one feels when catching a ball, or in the forward push a watercraft receives from a paddle-stroke. It is also what allows a rocket’s engine to provide thrust, even in space where there is seemingly nothing to “push” against.

For 10 points of extra credit, students can turn in the following by Tuesday:

Draw the free body diagram for the bottom textbook in a stack of textbooks resting on a table. Be sure to correctly label all of your forces, but you need not calculate their magnitude. Also include your axis labels.

Free-body diagrams this week in Physical Science (test on Friday!)

This week in Physical Science we will introduce the concept of free-body diagrams, an absolutely critical concept in the study of the forces acting on a system and how they will affect its motion. With the upcoming test on Friday, this week will be more focused on polishing the concepts of Newton’s Laws and forces already introduced; Thursday will be solely dedicated to answering students’ questions about the test the following day.

The following extra-credit question will appear on the test:

What are the three types of adult bees in Mr. Willco’s hives?

Students are of course welcome to study together if it will benefit their understanding of the material, but I ask that they not share this question with each other; they may absolutely share with their classmates that an extra-credit question is posted on the blog, but I want students to look up the information themselves.

Forces this week in Physical Science

This week in Physical Science we will be continuing our discussion of forces, including Newton’s Laws applications and free-body diagrams. A good understanding of forces is critical in the fields of physics and engineering, and consequently we will spend a significant amount of class time discussing the concept.

Owing to a delay in the delivery of critical components necessary for our velocity lab, it had to be delayed from last week till tomorrow; students will be analyzing the motion of and forces acting on battery operated motion buggies.

For 5 points of extra credit, students can answer the following question (due tomorrow, April 18th):

Mr. Willco has a mass of about 67 kg. What is the gravitational force (in N) acting on him if he were standing on the surface of Mars?

Concluding Momentum and Newton’s Laws this week in Physical Science

This week in Physical Science we will conclude our discussion of kinematics with some examples of momentum; we will then continue our discussion of Newton’s laws. We will also run our velocity lab later in the week.

As a reminder, students should come to class with the following materials every day:

  1.   A calculator
  2.  A whiteboard marker
  3. Their notes so far from this quarter
  4. A pencil
  5. Their agenda

For up to 10 points of extra credit, students can hand in a written response to the following questions:

On a recent launch, the first stage of the Falcon 9 spacecraft accelerated from rest to 4700 mi/hr in 2.5 minutes.

  1. What was the average acceleration (in m/s²) of the rocket during this time?
  2. What was the average acceleration in g’s (Earth gravitational g’s, not grams)?

All work and any relevant formulae must be shown. The calculations and answer should be on a separate sheet of paper from the textbook homework due tomorrow.

Newton’s Laws this week in Physical Science

This week in Physical Science we will be wrapping up our discussion of Kinematics and begin to discuss Newton’s Three Laws of Motion. Altho Newton first formulated these laws in 1687, they have proved well suited to most forms of motion even in the present day, over three hundred years later. They do break down where relativistic or quantum effects start to dominate, but fortunately, most of these situations are beyond the purview of a 7th grade science class.

For up to 5 points of extra credit, students can hand in the following problem in class on Monday:

A 747 jetliner has a cruising speed of about 250 m/s. Assuming it travels this speed for the entire flight (that is, neglecting time spent for take-off and landing), how long (in hours) would it take for a 747 to fly from Phoenix to New York City? Show all work, and clearly indicate what value you looked up for the distance from Phoenix to New York.

Kinematics continued this week in Physical Science

With AzMerit testing there will be less time in class than usual, but we will continue our discussion of kinematics this week. The concepts of velocity and acceleration will be further flushed out, and we will begin an introduction to momentum.

For 5 points of extra credit, students can provide a written response to the following question on Tuesday:

A student records her odometer and time as 19,652 miles and 7:19 am when she leaves home; when she arrives at school, her odometer and time readings are 19,659 miles and 7:32 am. What was the students average speed on the drive to school?

All work must be shown, and the answer should be written with 3 significant figures. This problem should take your student 10 minutes at most.

Introduction to Kinematics in Physical Science

Welcome back from Spring Break! This week in 7th Grade Physical Science we will be starting our introduction to kinematics; the Motion, Forces, and Energy textbook will be very useful for this topic, and students should plan on having it with them whenever they plan on doing homework or studying. Kinematics is the study of objects in motion, and the name is derived from the Greek kinein, which means “to move”. What we today call kinematics has been studied since antiquity, primarily for its application to warfare (the arc of a siege engine’s projectile is well described by basic kinematics), but also for the design and operation of simple machines such as pulleys or levers.

You may notice your child asking to record your vehicle’s odometer reading on their way to school this week: they will be using this information to calculate their average speed on their way to school.


In 7th Grade Physical Science this week, we will be continuing to examine density with an exciting laboratory activity… Ship ahoy!  We will then move on to examine the different properties of matter, both physical and chemical.  Try hunting around the house to find examples of physical and chemical changes.  Can you find both just by lighting a candle?