Energy and Its Forms 15.1 pg 446-452

Energy and Work Energy is the ability to do work Energy is transferred by a force moving an object through a distance Work is a transfer of energy When work is done on a n object, energy is transferred to that object

Example of work and energy: Carrying your backpack up stairs Lift it -- AGAINST the force of gravity REQUIRES energy from your MUSCLES Muscles REQUIRE energy from FOOD Food REQURIES energy from plants and other animals.

Kinetic Energy (KE) Is the energy of motion Depends on an objects velocity (speed) and mass The kinetic energy of any moving object depends upon its mass and speed Kinetic Energy (KE) = 1/2 m x v2 Where m = mass in kg and v = velocity in m/s

Sample Problem for KE: A 0.1 kg bird is flying at a constant speed of 8 m/s. What is the bird’s kinetic energy? Given info: Mass = 0.1 kg Speed or v = 8 m/s Step 1: KE = 1/2 mv2 Step 2: KE = 1/2 (0.1 kg) (8 m/s)2 Step 3: KE = 3.2 kgm2/sec2 = 3.2 kgm/sec2 m And because kgm/sec2 is a Newton we can write… KE = 3.2 Nm And Nm is a Joule so finally…KE = 3.2 Joules

Potential Energy (PE) Energy that is stored because of position or shape A stretched string on a guitar or a streched rubber band has potential energy (PE) Two types of PE: Gravitational Potential Energy Elastic Potential Energy

Gravitational Potential Energy(GPE) Potential energy that depends upon an object’s height An objects GPE depends on its mass, its height, and acceleration due to gravity Increases when an object is raised to a higher level GPE or PE = mgh Where m is mass, g is gravity, and h is height

Sample Problem for PE A 50 kg diver is at the top of a 10 meter high diving platform. What is the diver’s potential energy? Given info: Mass = 50 kg Height = 10 m Gravity = 9.8 m/sec2 Step 1: PE = mgh Step 2: PE = 50 kg (9.8m/sec2)(10m) Step 3: PE = 4900 kgm/sec2 m And because kgm/sec2 is a Newton we can write… PE = 4900 Nm And Nm is a Joule so finally…PE = 4900 Joules

Elastic Potential Energy (EPE) The potential energy of an object that is stretched or compressed Examples Stretched Ukulele string, rubber band, etc. Compressed Bouncing a ball, shocks on a car, etc.

Forms of Energy Mechanical: Both Kinetic and Potential together Thermal Chemical Electrical Electromagnetic Nuclear

Mechanical Energy (ME) The energy associated with the motion and position of everyday objects Sum of an objects Potential and Kinetic Energy Does not include thermal, chemical or other forms of energy associated with the motion or arrangement of atoms or molecules ME = PE + KE

Thermal Energy Atoms in an object are always in motion The total PE and KE of the molecules make up its thermal energy Faster motion, more thermal energy

Chemical Energy Chemical Energy is the energy stored in chemical bonds. When broken they release energy All chemical compounds store energy Gives energy from food Warm from firewood Energy from coal

Electrical Energy Energy associated with electric charges Batteries convert chemical energy into electric Lightning bolts

Electromagnetic Energy Electromagnetic energy is a form that travels through space in the form of waves Visible light X rays Gamma Rays Microwaves

Nuclear Energy The energy that is stored in atomic nucleus Nuclear power plants - fission - release energy The sun - Fusion - release energy when nuclei combine

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