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WHAT IS ENERGY?

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ENERGY:

- ability to do work.
Whenever work is done, energy is transformed or transferred to another system.

SI Units:

- joules (J)

- energy that an object has because of position, shape, or condition
- stored energy.

- energy stored in any type of stretched or compressed elastic material.
- spring
- rubber band

- energy stored in gravitational field which exists between any two or more objects.

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:

m = 65 kg

h = 35 m

g= 9.8 m/s2

PE = ?

WORK:

PE = mgh

PE = (65 kg) (35 m) (9.8 m/s2)

PE = 2.2 x 104kg•m2/s2

2.2 x 104 J

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

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

GIVEN:

KE = ?

m = 44 kg

v= 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

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

GIVEN:

KE = ?

m = 1500 kg

v= 29 m/s

WORK:

KE = ½ mv2

KE = ½ (1500 kg) (29 m/s)2

KE = 6.3 x105 J

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

GIVEN:

KE = ?

m = 1500 kg

v= 18 m/s

WORK:

KE = ½ mv2

KE = ½ (1500 kg) (18 m/s)2

KE = 2.4 x105 J

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)

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.

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