Ch. 5 - Energy I. Energy & Work (pp )  Energy  Work  Conservation of Energy  Thermal Energy

Make a table in your notes Type of Energy DescriptionExamples

A. Energy Types ENERGY The ability to cause change. motion of electric charges PE held in bonds between atoms Energy of moment/ potential movement internal energy of particles Energy released b/c of changes in the nucleus (fission or fusion) MECHANICAL CHEMICAL NUCLEARTHERMALHEAT ELECTROMAGNETIC El’c and mag’c energy in the form of waves transfer of energy b/c of a difference in temp. RADIANT/LIGHT ELECTRICAL “visible;” emitted by moving charged particles SOUND Measured in joules (J) Mechanical wave through medium

A. Energy Potential Energy (PE = mgh)  stored energy  depends on position or configuration of an object Which boulder has greater gravitational PE? What other ways can an object store energy?

A. Energy Kinetic Energy (KE = ½ mv 2 )  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?

A. Energy Problems Calculate the KE of a 40 kg girl running on a track at 15 m/s. Calculate the gravitational PE of a 50 kg boy at the top of the stadium (12.5 m).

B. 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

B. 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

B. 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

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

C. Conservation of Energy PE  KE View pendulum animation.pendulum animationView roller coaster animation.roller coaster animation

C. Conservation of Energy Mechanical  Thermal View rolling ball animations.rolling ball animationsView skier animation.skier animation