Energy Notes

Chapter 15Sections 1-2

Energy is the ability to do work. Energy is measured in Joules, just like work.

Work is a transfer of energy.

The energy of motion is called kinetic energy.

To calculate the kinetic energy of an object, multiply half the object’s mass (m) by its speed (v) squared. FORMULA: KE = ½ mv2

Potential energy is energy that is stored as a result of position or shape.

The potential energy of an object that is stretched or compressed is known as elastic potential energy.

The kinetic energy of any moving object depends upon its mass and speed.

Potential energy that depends on an object’s height is called gravitational potential energy.

Gravitational potential energy is calculated by multiplying the object’s mass (m) by the acceleration due to gravity (g) and its height above the ground (h).

FORMULA: GPE = mgh g = 9.8 m/s/s

An object’s gravitational potential energy depends on its mass, its height, and the acceleration due to gravity.

Find the kinetic energy of a 0.1kg toy truck moving at a speed of 1.1 m/s.

KE = ½ mv2

KE = ½ (0.1kg)(1.1m/s)2 KE = 0.0605 Joules

Energy calculation examplesKE = ½ mv2 GPE = mgha. Write the formulab. Plug-in the numbers with unitsc. Write the answer with units

A book on a shelf 2m above the floor has a mass of 1.5kg. What is the gravitational potential energy of the book?

GPE = mgh GPE = (1.5kg)(9.8m/s/s)(2m) GPE = 29.4 Joules

Energy calculation examplesKE = ½ mv2 GPE = mgha. Write the formulab. Plug-in the numbers with unitsc. Write the answer with units

Which runner has the greater kinetic energy: a 46kg runner moving at a speed of 8 m/s or a 92kg runner moving at a speed of 4 m/s?

Energy calculation examplesKE = ½ mv2 GPE = mgha. Write the formulab. Plug-in the numbers with unitsc. Write the answer with units

Runner 1KE = ½ mv2

KE = ½ (46kg)(8m/s)2

KE= 1472 Joules

Runner 2KE = ½ mv2 KE = ½ (92kg)(4m/s)2 KE = 736 Joules

If a 6kg box is moved from the floor to a storage compartment 2m above the floor, by how many joules does its potential energy change?

GPE = mgh GPE = (6kg)(9.8m/s/s)(2m) GPE = 117.6 Joules

Energy calculation examplesKE = ½ mv2 GPE = mgha. Write the formulab. Plug-in the numbers with unitsc. Write the answer with units

The total energy of motion (KE) and position (PE) of any object is its mechanical energy (ME).

FORMULA:ME = PE + KE Sound energy is a form of mechanical energy.

It involves the compression and expansion of air particles, thus has both kinetic and elastic potential energy.

The total potential and kinetic energy of all the microscopic particles in an object make up its thermal energy. This is also known as heat energy.

The major forms of energy are…

Chemical energy is the energy stored in chemical bonds.

Electrical energy is the energy associated with electrical charges.

Electromagnetic energy is a form of energy that travels through space in the form of waves. This includes light energy, x-rays, microwaves, and other forms of electromagnetic waves.

Nuclear energy is energy stored in the nuclei of atoms (fission, fusion).

The major forms of energy are…

The process of changing energy from one form to another is energy conversion.

Every energy conversion involves some conversion to thermal energy due to friction.

Energy can be converted from one form to another.

When energy changes from one form to another, the total amount of energy stays the same.

The gravitational potential energy of an object is converted to the kinetic energy of motion as an object falls.

The law of conservation of energy states that energy cannot be created or destroyed.