EF CH 13: Energy and Power01

Engineering Fundamentals: CH 13 Energy and Power 01

Open Ended

Why do we care about energy in engineering?

Energy is required for everything.

We need energy to

• build shelters and other structures

• make products

• process and cultivate food

• heat or cool buildings and other things

• move or lift objects

and energy isn't free

-Tesla didn't deliver

Officially

Energy is the ability to do work.

• available in various forms:

  • kinetic

  • potential

  • elastic

  • thermal

Kinetic Energy

Energy of motion

Kinetic Energy = 1/2 mass x velocity ²

Kinetic Energy

Mechanical work performed on an object changes its kinetic energy.

​Work = 1/2 mass x velocity² - 1/2 mass x velocity²

^{at the end initially}

Multiple Choice

Based on what we have discussed so far, larger objects going at the same speed will

• be easier to stop

• have higher kinetic energy

• have lower kinetic energy

Multiple Choice

Smaller changes in velocity (with the same object) will result in

• larger amounts of work

• smaller amounts of work

• no work

• snails

Multiple Choice

To minimize the work required, which of the following should you do?

• keep the change in velocity as small as possible for similarly weighing objects

• grow the change in velocity as much as possible for similarly weighing objects

• use as heavy an object as you can find

• Increase the number of objects being weighed

Potential Energy

Energy of position, work required

to lift an object, it's the energy to overcome gravity

change in potential energy = mass x gravity x change in height

Multiple Choice

How does a greater change in height affect potential energy?

• it increases the potential energy

• it decreases the potential energy

• it is unrelated

Multiple Choice

Based on our formula for potential energy, to increase the potential energy of a situation, you should always

• minimize the change in height

• minimize the mass of the object lifted

• maximize the change in height

• Increase the force applied to the object

Elastic Energy

• When a spring is stretched or compressed from its unstretched position, elastic energy is stored in the spring

• Energy will be released when the spring is allowed to return to its unstretched position

Elastic Energy

• Elastic energy =

  1/2 spring constant x distance stretched²

the spring constant for a specific spring is based

on a comparison of how force causes the

spring to move, or how stiff it is

Multiple Choice

The spring constant

• is 9.81 m/s²

• varies depending on the stiffness of the spring

• does not affect elastic energy of a spring

• is equal to the speed of light

Thermal Energy

• is transferred whenever there exists a temperature difference within an object, between two bodies, or between a body and its surroundings

• heat flows from high to low temperature

Thermal Energy Modes

Three modes of heat transfer

• Conduction

• Convection

• Radiation

Multiple Choice

Thermal energy transfer occurs when

• When two objects come into contact and exchange backwards momentum

• cold transfers from a low temperature region to a high temperature region

• heat transfers from a high temperature region to a lowtemperature region

• When an object is exposed to a magnetic field

Multiple Choice

Thermal energy along the handle of a pot on a burner is most like

• conduction

• convection

• reflection

• radiation

Multiple Choice

Thermal energy inside a boiling pot of water on a burner is most like

• conduction

• convection

• reflection

• radiation

Match

Match the following equations to their type of energy:

• kinetic energy

• change in potential energy

• elastic energy

1/2 mass x velocity²

mass x gravity x change in height

1/2 spring constant x distance stretched ²

• 1/2 mass x velocity²

• mass x gravity x change in height

• 1/2 spring constant x distance stretched ²