WHAT IS ENERGY?

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 ENERGYA 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:

m = 65 kgh = 35 mg= 9.8 m/s2

PE = ?

WORK:PE = mghPE = (65 kg) (35 m) (9.8 m/s2)

PE = 2.2 x 104 kg•m2/s2

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 1

2mass speed squared

KE 1

2mv 2

KINETIC ENERGY

What is the kinetic energy of a 44 kg cheetah running at 31 m/s?

GIVEN:

KE = ?m = 44 kgv= 31 m/s

WORK:KE = ½ mv2

KE = ½ (44 kg) (31 m/s)2

KE = 2.1 x 104 kg x m2/s2 or 2.1 x104 J

KINETIC ENERGY

Calculate the kinetic energy in joules of a 1500 kg car moving at 29 m/s.

GIVEN:

KE = ?m = 1500 kgv= 29 m/s

WORK:KE = ½ mv2

KE = ½ (1500 kg) (29 m/s)2

KE = 6.3 x105 J

KINETIC ENERGY

Calculate the kinetic energy in joules of a 1500 kg car moving at 18 m/s.

GIVEN:

KE = ?m = 1500 kgv= 18 m/s

WORK:KE = ½ mv2

KE = ½ (1500 kg) (18 m/s)2

KE = 2.4 x105 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