5.2 Energypp 172 -180

Mr. Richter

Agenda

Warm-Up

Review HW

Introduction to Energy

Notes: Kinetic Energy Potential Energy

Gravitational Other forms

Work and Energy

Lab Friday

Objectives: We Will Be Able To…

Define energy and identify several forms of energy.

Define and calculate kinetic energy.

Classify, define and calculate different types of potential energy.

Understand the relationship between work and energy.

Warm-Up:

Review: What is energy? You may need to review your notes from the first week of

school.

Write a 1-sentence definition in your notes.

Energy

What is Energy?

Review: Energy is a measure of the ability to cause change in a system.

Energy is like the currency of the universe. Physics money. If you have energy, you can

make a change. If you have no energy, no

change can be made.

Kinetic EnergyThe Energy of Motion

Kinetic Energy

Objects in motion have the ability to cause change. A moving wrecking ball can cause

change in the shape of a building. Moving hands can cause a change in

temperature.

Kinetic energy is the energy of an object due to its motion.

You can also think of kinetic energy as the amount of energy that would have to be used to stop an object.

Kinetic Energy

Kinetic energy depends on: mass speed

Units: mass x speed2 = [kg x (m/s)2] = [(kg x m/s2)(m)] = N-m =

J! The units of energy (all forms) are Joules [J]!

Warm Up: Calculating Kinetic Energy

A 7.00 kg bowling ball moves at 3.00 m/s. How much kinetic energy does the bowling ball have?

31.5 J

Potential EnergyThe Energy of Position

Potential Energy

The word potential implies that something could happen. An object could cause a change.

Objects in certain positions have the potential to cause change. Potential energy is the energy associated with the object due to the position of the object.

Potential energy is stored energy.

Gravitational Potential Energy

Falling objects gain speed, and therefore gain the ability to cause change. Therefore, any object positioned to fall has potential energy.

Gravitational potential energy is the energy of an object due to its position relative to the Earth (or other source of gravity).

Gravitational potential energy depends on how far something will fall, not necessarily its distance from the ground: height.

Calculating Gravitational Potential Energy

A 20.0 kg anvil is positioned to crush the roadrunner 15.0 m below. How much potential energy does the anvil have?

Other types of Potential Energy

Elastic: when a spring or rubber band is stretched or compressed

Electrical: when electrons want to move from one place to another

Work and EnergyTwo peas in a pod.

Work and Energy

Another definition for work:

The amount of energy transferred from one object to another, or from one form to another. Work done = change in energy

The amount of work needed to speed up an object is equal to the change in kinetic energy of the object.

The amount of work needed to lift an object is equal to the change in the potential energy of the object.

Calculations with Work and Energy

Wnet = ΔKE

Wnet = ΔPE

A 75 kg bobsled is pushed along a horizontal surface by two athletes. After the bobsled is pushed a distance of 4.5 m starting from rest, its speed is 6.0 m/s. Find the magnitude of the net force on the bobsled.

Wrap-Up: Did we meet our objectives?

Homework