Ch. 4 - EnergyCh. 4 - Energy

I. Energy and Work (p.100-123) Energy Work Conservation of Energy

A. EnergyA. Energy

ENERGY

motion of electric chargesbonding of atoms

motion of objects

internal motion of particles

changes in the nucleus

The ability to cause change.

MECHANICAL

ELECTRICALCHEMICAL

NUCLEAR

THERMAL

joules (J)

A. EnergyA. EnergyKinetic 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. EnergyA. EnergyPotential 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. WorkB. WorkWork

transfer of energy through motion force exerted through a distance

W = FdDistance must be in direction of force!

W: work (J)F: force (N)d: distance (m)

1 J = 1 N·m

B. WorkB. WorkBrett’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 Nd = 1.5 mW = ?

WORK:W = F·dW = (30 N)(1.5 m)W = 45 J

FWd

B. WorkB. 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 kgd = 1.4 m - duringd = 2.2 m - afterW = ?

WORK:W = F·d F = m·aF =(40kg)(9.8m/s2)=392 NW = (392 N)(1.4 m)W = 549 J during liftNo work after lift. “d” is not in the direction of the force.

FWd

C. Conservation of EnergyC. Conservation of EnergyLaw 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 EnergyC. Conservation of EnergyPE KE

View pendulum animation. View roller coaster animation.

C. Conservation of EnergyC. Conservation of EnergyMechanical Thermal

View rolling ball animations. View skier animation.