WHAT IS ENERGY ENERGY ability to do work

WHAT IS ENERGY?

ENERGY: • ability to do work. Whenever work is done, energy is transformed or transferred to another system. SI Units: • joules (J)

POTENTIAL ENERGY • energy that an object has because of position, shape, or condition • stored energy.

ELASTIC POTENTIAL ENERGY • energy stored in any type of stretched or compressed elastic material. • spring • rubber band

GRAVITATIONAL POTENTIAL ENERGY • energy stored in gravitational field which exists between any two or more objects. • depends on both mass and height. • PE = mgh

GRAVITATIONAL POTENTIAL ENERGY A 65 kg rock climber ascends a cliff. What is the climber’s gravitational potential energy at a point 35 m above the base of the cliff? GIVEN: WORK: m = 65 kg h = 35 m g= 9. 8 m/s 2 PE = ? PE = mgh PE = (65 kg) (35 m) (9. 8 m/s 2) PE = 2. 2 x 104 kg • m 2/s 2 2. 2 x 104 J

Kinetic Energy • energy of a moving object due to object’s motion • depends on mass and speed. • depends on speed more than mass.

KINETIC ENERGY What is the kinetic energy of a 44 kg cheetah running at 31 m/s? GIVEN: WORK: KE = ? m = 44 kg v= 31 m/s KE = ½ mv 2 KE = ½ (44 kg) (31 m/s)2 KE = 2. 1 x 104 kg x m 2/s 2 or 2. 1 x 104 J

KINETIC ENERGY Calculate the kinetic energy in joules of a 1500 kg car moving at 29 m/s. GIVEN: WORK: KE = ? m = 1500 kg v= 29 m/s KE = ½ mv 2 KE = ½ (1500 kg) (29 m/s)2 KE = 6. 3 x 105 J

KINETIC ENERGY Calculate the kinetic energy in joules of a 1500 kg car moving at 18 m/s. GIVEN: WORK: KE = ? m = 1500 kg v= 18 m/s KE = ½ mv 2 KE = ½ (1500 kg) (18 m/s)2 KE = 2. 4 x 105 J

OTHER FORMS OF ENERGY MECHANICAL ENERGY: • amount of work an object can do because of object’s kinetic & potential energies • you can SEE it • Large scale basis NONMECHANICAL ENERGY. • you CANNOT SEE it • X rays, microwaves • Small scale basis (atomic)

OTHER FORMS OF ENERGY ATOMS AND MOLECULES • kinetic energy of particles related to heat and temperature. CHEMICAL REACTIONS • Breaking bonds exothermic/endothermic PHOTOSYNTHESIS • turn energy in sunlight into chemical energy.

OTHER FORMS OF ENERGY NUCLEAR FUSION /FISSION REACTIONS • Combining or splitting of atomic nuclei ELECTRICITY. • flow of charged particles • bolt of lightning or in a wire. ELECTROMAGNETIC WAVES. • Light energy (solar) from sun • X rays