Ch. 4 - Energy I. Energy and Work (p )  Energy  Work  Conservation of Energy

A. 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)

A. 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?

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

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