Forms of Energy ENERGY motion of electric charges bonding of atoms motion of objects internal motion of particles changes in the nucleus The ability to cause change. MECHANICAL ELECTRICAL CHEMICAL NUCLEARTHERMAL joules (J)

Energy and Work Energy is the ability to do work Work is a transfer of energy Always measured in joules (J)

Forms of Energy The energy associated with motion and position of everyday objects is mechanical energy Not limited to machines It is the sum of an object’s potential energy and kinetic energy

Forms of Energy The total potential and kinetic energy of all the microscopic particles in an object make up its thermal energy When an object’s atoms move faster, its thermal energy increases and the object becomes warmer

Forms of Energy Chemical energy is the energy stored in chemical bonds When the bonds are broken, the released energy can do work

Forms of Energy Electrical energy is the energy associated with electric charges Electricity also comes from nature  -EX: Lighting

Forms of Energy Electromagnetic energy is a form of energy that travels through space in the form of waves EX: -Light from the sun, X-rays They can travel long distances

Forms of Energy The energy stored in atomic nuclei is known as nuclear energy The nucleus of an atom is held together by strong and weak nuclear forces, which can store an enormous amount of potential energy

Energy Kinetic Energy (KE)  energy in the form of motion  depends on mass and velocity 80 km/h 50 km/h 80 km/h 80 km/h truck 50 km/h motorcycle Which has the most KE? Which has the least KE?

Kinetic Energy To calculate the kinetic energy of an object in joules, multiple ½ by the objects mass (m) in kilograms and the square of its speed (v) in meters per second ½ mv

Energy Potential Energy (PE)  stored energy  depends on position or configuration of an object Which boulder has greater gravitational PE?

Gravitational Potential Energy Potential energy depends upon an object’s height Increases as an object is raised Depends on its mass, its height, and the acceleration due to gravity SI unit due to gravity is 9.8 m/s Is equal to its weight (mg) multiplied by its height (h) PE = mgh

Gravitational Potential Energy Suppose the diver at the top of a 10 meter high diving platform has a mass of 50 kilograms. What is her potential energy relative to the ground? PE = mgh = (50 kg)(9.8 m/s )(10 m) = 4900 kg m /s = 4900 J

Elastic Potential Energy The potential energy of an object that is stretched or compressed Something elastic springs back to its original shape after it is stretched or compressed EX: -Rubber band / springs, potential energy is converted into kinetic energy

Work Work  transfer of energy through motion  force exerted through a distance W = Fd Distance must be in direction of force! W:work (J) F:force (N) d:distance (m) 1 J = 1 N·m

Work Work Brett’s backpack weighs 30 N. How much work is done on the backpack when he lifts it 1.5 m from the floor to his back? GIVEN: F = 30 N d = 1.5 m W = ? WORK: W = F·d W = (30 N)(1.5 m) W = 45 J F W d

Work A dancer lifts a 40 kg ballerina 1.4 m in the air and walks forward 2.2 m. How much work is done on the ballerina during and after the lift? GIVEN: m = 40 kg d = 1.4 m - during d = 2.2 m - after W = ? WORK: W = F·dF = m·a F =(40kg)(9.8m/s 2 )=392 N W = (392 N)(1.4 m) W = 549 J during lift No work after lift. “d” is not in the direction of the force. F W d

Conservation of Energy Conservation of Energy Law of Conservation of Energy  Energy may change forms, but it cannot be created or destroyed. EX:  PE  KE  mechanical  thermal  chemical  thermal

Conservation of Energy Conservation of Energy If you stop pedaling when you’re riding a bike on a flat path, the bike will eventually come to a stop. The moving bike had kinetic energy, so where did it go?

Conservation of Energy Conservation of Energy The bike stopped because of friction. The friction changed the kinetic energy to thermal energy.

Energy Conversion Energy can be converted from one form to another Some conversion takes a series of steps EX: - Lighting a match

Energy Conversion When you light a match, your muscles use chemical energy moving your hand to strike the match. Friction between the match and the match box converts it into thermal energy. The thermal energy triggers a chemical reaction, releasing the match’s stored chemical energy. This is then converted into thermal and electromagnetic energy in the flame.

Energy Conversions One of the most common energy conversions is between potential and kinetic energy The gravitational potential energy of an object is converted to the kinetic energy of motion as the object falls EX: -Avalanche

Energy Conversions Pendulums -Were used in the first accurate clocks -It consists of a weight swinging back and forth from a rope or string -Time it takes for a pendulum to swing back and forth once is related to its length

Energy Conversions Energy Conversion Calculations -Mechanical energy = KE + PE -If friction can be neglected, than the mechanical energy in the beginning equals the mechanical energy at the end

Energy and Mass Albert Einstein developed the theory of relativity The theory included the famous equation E = mc E = energy, M = mass, and C = the speed of light This equation states that energy and mass are equivalent and can be converted into each other