Energy IPC Physical Science, Mr. Hayhurst, Lancaster High School

What is Energy? Energy is the ability to do work. So, what is work? force distance Work is a quantity that measures the effects of a force acting over a distance Work is done only when a force moves an object.

What is Work? If an object does not move in the direction of the force when a force is applied to it, no work is done. Work is measured in Joules. –1 Joule (J) = 1 N  m Work = force × distanceW = F×d –Force is measured in Newtons (N). –Distance is measured in meters (m).

What is Work? Energy is always transferred … –from the object doing the work –to the object on which work is done Practice problems Remember… –You cannot get more work out of a system than what you put into the system.

What is Power? Power is the quantity that measures the rate at which work is done –how quickly work is done The same amount of work done faster will produce more power. Power is measured in watts. Power = work ÷ time P = Work time

What is Energy? A Newton times a meter equals a Newton-meter or a joule. Energy is then measured in Newton- meters or joules. Joule = a unit of energy = Newton-meter = kg  m 2 /s 2

Example How much energy does it take to move a 200 N mass a distance of 25 m? W = 200 N  25 m W = 5000 Nm W = 5000 joules

Types of Energy There are two types of energy; –Potential Energy –Kinetic Energy

Potential Energy Potential Energy is energy that is stored up in some form. Formula for solving P.E. is; P.E. = mgh m = mass g = gravitational constant 9.8 m/s/s or 9.8 m/s 2 h = height

Sample P.E. Problem How much Potential Energy does a 164 kg mass have at the height of 0.73 meters? P.E. = 164 kg  9.8 m/s/s  0.73 m = 164 kg  m 2 /s 2 = 1173 kg  m 2 /s 2 = 1173 joules

Kinetic Energy Kinetic Energy is the energy an object has because of its state of motion. Formula for solving K.E. is; K.E. = ½ mv 2 m = mass v = velocity

Sample K.E. Problem How much kinetic energy does a ball with a mass of 0.4 kg traveling at a speed of 28 m/s have? K.E. = ½(0.4 kg)  (28 m/s) 2 = 0.2 kg  784 m 2 /s 2 = kg  m 2 /s 2 = joules

Quiz Directions: First identify weather the object has Potential Energy or Kinetic Energy. Then solve for PE or KE. 1.A box on the shelf 2 meters high with a mass of 20 kg. 2.A ball rolling along a shelf that has a velocity of 5 m/s and a mass of 100 g. 3.A marble with a mass of 15 g at the top of a 15 cm tall slope. 4.A weight bar and weights that have a mass of 250 kg lifted up to a height of 2.5 m. 5.An automobile with a mass of 2000 kg and a velocity of 50 m/s.

Checking Your Answers 1.A box on the shelf 2 meters high with a mass of 20 kg. Potential Energy P.E. = 20 kg  9.8 m/s 2  2 m P.E. = joules

Checking Your Answers 2.A ball rolling along a shelf that has a velocity of 5 m/s and a mass of 100 g. Kinetic Energy K.E. = ½(0.1 kg)  (5 m/s) 2 K.E. = 1.25 joules

Checking Your Answers 3.A marble with a mass of 15 g at the top of a 15 cm tall slope. Potential Energy P.E. = kg  9.8 m/s 2  0.15 m P.E. = joules

Checking Your Answers 4.A weight bar and weights that have a mass of 250 kg lifted up to a height of 2.5 m. Potential Energy P.E. = 250 kg  9.8 m/s 2  2.5 m P.E. = 6125 joules

Checking Your Answers 5. An automobile with a mass of 2000 kg and a velocity of 50 m/s. Kinetic Energy K.E. = ½(2000 kg)  (50 m/s) 2 K.E. = 2,500,000 joules

Forms of Energy Six forms of energy are: Mechanical Energy Heat Energy Electromagnetic Energy Chemical Energy Radiant Energy Nuclear Energy

Mechanical Energy Mechanical energy is the energy of a moving object. Examples are: –Bowling ball –Sound –Moving object Can be both potential and kinetic.

Heat Energy Heat Energy is associated with the movement of particles that make up matter. It is related to changes in state as well as changes in temperature.

Electromagnetic Energy Involves Electricity and Magnetism. Electrical energy involves the movement of a stream of electrons through a field of magnetism. Electricity can cause magnetism. Magnets can cause electrical currents. Can exist in both P.E. and K.E.

Chemical Energy Chemical energy is associated with the formation and break-up of chemical compounds. Gasoline contains potential chemical energy that becomes kinetic when it is burned.

Nuclear Energy Nuclear Energy is the energy produced when the nuclei of atoms split or combine. This energy comes from the conversion of small amounts of mass into heat and light energy.

Radiant Energy Radiant Energy is energy that is transmitted through space in the form of waves. Radiant Energy includes: visible light radio waves radar waves infrared light ultraviolet radiation X-rays

Energy Transformation Energy is always changing from one form to another. –The Sun, primary source of energy on the Earth. –Nearly all energy comes from the sun. –Energy cannot be created or destroyed. (AKA: Law of Conservation of Energy)

The Flow of Energy The Sun, Nuclear Energy Earth Energy received by the Earth is converted into heat and chemical energy. The Sun gives off Radiant energy in the form of light

The Flow of Energy Plants convert light (radiant energy) into chemical energy (sugar or glucose) through a process called Photosynthesis. When light from the Sun hits the Earth the radiant energy is transformed into heat energy.

Energy Transformation There are many examples of energy transformations. Give an example for each arrow in the following diagram. Electromagnetic Radiant Chemical Nuclear Mechanical Heat

Energy The End Copyright © 2000, Pat Hayhurst Lancaster High School