Chapter 4-- Energy

Section 1: The Nature of Energy What is Energy— Energy is present all around us all day Energy changes are taking place constantly Ex: baseball flying and hitting a window, combing your hair, walking to class, etc

Energy is the ability to cause change Anything that causes change must have energy There are many different forms of energy including electrical, chemical and thermal

Kinetic Energy -is energy in the form of motion Ex: spinning wheel, sprinting runner, football passing through goalposts Amounts of Kinetic Energy depend on two quantities: mass and velocity (more mass = more energy) (more velocity = more energy)

Calculating Kinetic Energy The equation for calculating kinetic energy is: Kinetic energy = ½ mass X velocity^2 Joule—the SI unit of energy

Potential energy -is stored energy due to position Objects that have potential energy have the ability to cause change Elastic Potential Energy= energy stored by something that can stretch or compress (ex: rubber band) Chemical Potential Energy = energy stored in chemical bonds (ex: atoms)

Gravitational Potential Energy (GPE) Gravitational Potential Energy is energy stored by objects that are above Earth’s surface The amount depends on the MASS of the object, Acceleration Due to Gravity and HEIGHT above the ground GPE = mass X 9.8 m/s/s X height (GPE is measured in Joules also)

Section 2: Conservation of Energy Transforming electrical energy Happens all day, everyday Ex: lightbulbs transform electrical energy into light Some of the electrical energy is turned into thermal energy (hot bulbs) Ex: alarm clock, straighteners, toaster, etc.

Transforming chemical energy: Fuel is stored in the form of chemical potential energy Ex: Engines transform chemical potential energy stored in gas into kinetic energy Ex: Green plants convert light energy from the Sun into stored energy in chemical bonds

Conversions between kinetic and potential energy Many situations involve conversions between potential and kinetic energy Ex: bicycles, roller coasters, swings, etc. Mechanical energy is the total amount of potential and kinetic energy in a system Mechanical energy = GPE + KE

When energy is transformed from potential to kinetic, the potential energy is not LOST, it has simply been converted, but the total amount of energy remains the same Ex: Pg. 109—apple tree, baseball, swing

Law of Conservation of Energy: Kinetic and potential energy are constantly changing as the object speeds up and slows down However, mechanical energy (total energy) stays constant So: -Energy cannot be created or destroyed, it simply changes form

Friction and the Law of Conservation of Energy Friction slows moving objects, which seems to decrease mechanical energy of an object. However, friction converts energy to other forms such as thermal energy (heat)

Converting Mass into Energy Nuclear fusion—a special kind of energy conversion During this process a small amount of mass is transformed into a tremendous amount of energy by fusing atomic nuclei (sun) Nuclear fission—similar process, but nuclei are broken apart, not fused together

Human Body –Energy Conversions Complex chemical and physical processes in the body obey the law of conservation of energy Energy is stored as fat and converted to energy as needed for life processes 1 Calorie (C) is equal to 4,184 J Every gram of fat supplies 9 C of energy Section 2 Assessment questions