ENERGY – WORK - POWER

THE LAW OF CONSERVATION OF ENERGY: Energy may not be created nor destroyed – it may only be transferred from one form to another. The total amount of energy in the universe is constant.

FORMS OF ENERGY: 1.MECHANICAL (POTENTIAL AND KINETIC) 2.ELECTRICAL 3.HEAT 4.LIGHT (electro-magnetic spectrum) 5.CHEMICAL 6.NUCLEAR 7.SOUND 8.MASS (E =mc2)

TYPES OF MECHANICAL ENERGY: KINETIC – POTENTIAL GRAVITATIONAL – ELASTIC – Energy due to motion. Symbol: KE Formula: KE=1/2mv2 Unit: Joule (J) Energy stored due to position or state of being. Symbol: PE Unit: Joule (J) (PEg) Energy stored by an object due to its position above some reference point Formula: PEg= mgh (PEs) Energy stored in a material due to its stretch Formula: PEs = 1/2kx2 (k = spring constant)

HOOKE’S LAW HOOKE’S LAW SLOPE: Force (N) AREA: Stretch (m) The stretch of a material is directly proportional to the force exerted on it. Formula: F = kx PEs Spring constant Elastic potential energy Stretch (m)

EXAMPLE: A 15kg block is hung from a spring that has a spring constant of 250 N/m. (a) How far will the spring stretch? (b) How much energy will be stored in the spring?

CONSERVATION OF ENERGY THE PENDULUM At the highest point: PEg = max KE = 0 At the lowest point: PEg = 0 KE = max At every point: DKE = DPEg

KINEMATICS OR CONSERVATION ? vf2 =vi2 + 2ad vf = [(2)(9.81m/s2)(55m)]1/2 vf = 32.8m/s 55m Energy PEg top = KEbottom mgh = 1/2mv2 v = [2gh]1/2 v = [(2)(9.81m/s2)(55m)]1/2

WORK – WORK – WORK DEFINITION – SYMBOL - UNIT - EQUATION – W JOULE (J) Exerting a force to move an object in opposition to some other force or any time kinetic energy is changed NO MOTION = NO WORK DEFINITION – SYMBOL - UNIT - EQUATION – W JOULE (J) W = F d = Fdcosq Only the component of the force in the direction of the displacement does work. Fcosq q

POWER DEFINITION SYMBOL - FORMULA – UNITS - P The RATE at which work is done P W Fd P = = = Fv t t Watt (W)

ROLLER COASTERS

Biological effects of energy conservation.

Example problem: Buzz pushes a crate across a carpeted floor a distance of 5 meters by applying a 75 Newton (net) force horizontally. How much work is done? What force is the work done against? If the crate is moved in 2 seconds, what is Buzz’s power output?

Example problem: Buzz and Click start at their adjoining lockers in the hall outside of the large cafeteria where they pick up their physics books. Buzz takes the hallway along the health office and through the L.O.T.E. wing coming up the stairs and into room 217, Click walks through the Viking Mall and takes the elevator up to the second floor, walks through the math wing then back down the stairs, through the tech hall and up the same stairs as Buzz before coming into the class room. Who did more work against gravity on the physics book?

Example problem: Click pulls a crate to the top of a smooth ramp by applying a force of 100 Newtons to a rope which is parallel to the ramp. If the ramp is 8 meters long and makes an angle of 300 with the ground, how much work does Click do against gravity?

Example problem: A sled is pulled by a boy who is applying a force of 200 N to the sled’s handle which makes an angle of 200. How much work does the boy do if he moves the sled 50 meters at a constant speed?

Example problem: How much work is done against gravity by a person who slides a box off of one table and places it on another table of the same height three meters away?

CONSERVATION OF MECHANICAL ENERGY THE PENDULUM PEg = max KE = 0 h PEg = 0 KE = max