# WHAT IS ENERGY? - PowerPoint PPT Presentation

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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.

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WHAT IS ENERGY?

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### 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:

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

### 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:

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

### KINETIC ENERGY

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

### KINETIC ENERGY

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

### 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