Energy Flow diagram

Page 3

This text is meant to accompany class discussions. It is not everything there is to know about energy. It is meant as a prep for class. More detailed notes and examples are given in the class notes, presentations, and demonstrations (click here.)

Reading questions for this unit.

Law of conservation of energy (for mechanical energies)

The first law of thermodynamics says that all energy is conserved. This is referred to as the law of conservation of energy. This means if you are sitting, at rest, at the top of a playground slide and then slide down to the bottom, all the forms of energy at the top and the bottom of the slide add up to give the same number. It is written like the the line shown below.

If this expression is applied to the slide example above, it would be written as

Since only two forms of energy are being considered, it could further be described as

Energy comes in many forms. Here, things are kept simple by only considering two forms, kinetic and gravitational potential energy.

Practice

Click here is the YouTube video above does not show up, http://youtu.be/fP8FPyRWAj8

Practice

Question
Solution

A basketball player tosses a ball upwards to its apogee. Use energy methods to find the ball's initial velocity.

Strategy

Use conservation of energy to solve. This means you need to pick two locations and compare their energies. on location is dictated by the question. You are to find the velocity of the ball when the player throws it. This in one of the locations. The second location is the place where you know both energies. This means you need to know the velocity and the height above the other location. It this problem the second location is 7 m above the starting height.

Solution

This video can be found at https://youtu.be/HZUNS5DiTJ8

Practice

Question
Solution

Given the information shown below, calculate the speed of the wagon on the far right at the given height.

Strategy:

Because there are no other forces outside of gravity acting on the wagon, you can use conservation of energy relationships to solve.
Pick two locations and compare their respective energies.
One of the locations is determined by the question. This will be the location at the far right as identified by the picture.
The other location will be somewhere where you know all the energies. In this case that will be at the far left.
Set up and solve as shown below. The blue text is not part of the actual solution. It is my notes about the solution and what must be shown.

Solution

This video can be found on YouTube at https://youtu.be/jhd59IfYKHA

by Tony Wayne ...(If you are a teacher, please feel free to use these resources in your teaching.)

The owner of this website does not collect cookies when the site is visited. However, this site uses and or embeds Adobe, Apple, GoDaddy, Google, and YouTube products. These companies collect cookies when their producs are used on my pages. Click here to go to them to find out more about how they use their cookies. If you do not agree with any of their policies then leave this site now.