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Energy. Energy and Work Energy Work Conservation of Energy. THERMAL. The ability to cause change. Kinetic. NUCLEAR. ELECTRICAL. CHEMICAL. joules (J). Energy. ENERGY. internal motion of particles. Potential . Stored energy . changes in the nucleus. motion of objects.

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Energy

Energy

Energy and Work

Energy

Work

Conservation of Energy


Energy1

THERMAL

The ability to cause change.

Kinetic

NUCLEAR

ELECTRICAL

CHEMICAL

joules (J)

Energy

ENERGY

internal motion of particles

Potential

Stored energy

changes in the nucleus

motion of objects

motion of electric charges

bonding of atoms


What is energy

What is energy

  • Wherever you are sitting as you read this, changes are taking place—lightbulbs are heating the air around them, the wind might be rustling leaves, or sunlight might be glaring off a nearby window.

  • Every change that occurs—large or small—involves energy.


Change requires energy

Change Requires Energy

  • When something is able to change its environment or itself, it has energy. Energy is the ability to cause change.

  • Anything that causes change must have energy


Different forms of energy

Different Forms of Energy

  • Energy has several different formselectrical, chemical, radiant, and thermal.

  • Is the chemical energy stored in food the same as the energy that comes from the Sun or the energy stored in gasoline?


Different forms of energy1

Different Forms of Energy

  • Radiant energy from the Sun travels a vast distance through space to Earth, warming the planet and providing energy that enables green plants to grow.


An energy analogy

An Energy Analogy

  • If you have $100, you could store it in a variety of formscash in your wallet, a bank account, travelers’ checks, or gold or silver coins.

  • You could transfer that money to different forms

  • You could deposit your cash into a bank account or trade the cash for gold.


An energy analogy1

An Energy Analogy

  • Regardless of its form, money is money.

  • The same is true for energy.

  • Energy from the Sun that warms you and energy from the food that you eat are only different forms of the same thing.


Energy2

  • Which has the most KE?

  • Which has the least KE?

80 km/h

50 km/h

80 km/h

Energy

  • Kinetic Energy (KE)

    • energy in the form of motion

    • depends on mass and velocity

    • if you double the velocity, you increase KE by four

80 km/h truck

50 km/h motorcycle


Kinetic energy ke

Kinetic Energy (KE)

  • The SI unit of energy is the joule, abbreviated J.

  • If you dropped a softball from a height of about 0.5m, it would have a kinetic energy of about one joule before it hit the floor.


Potential energy

Potential Energy

  • Even motionless objects can have energy. This energy is stored in the object.

  • A hanging apple in a tree has stored energy

  • Stored energy due to position is called potential energy.


Energy3

Energy

  • Potential 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?


Elastic potential energy

Elastic Potential Energy

  • If you stretch a rubber band and let it go, it sails across the room. It gains kinetic energy.

  • As it flies through the air, it has kinetic energy due to its motion.

  • Where did this kinetic energy come from?

  • The stretched rubber band had energy stored as elastic potential energy.

  • Elastic potential energy is energy stored by something that can stretch or compress, such as a rubber band or spring.


Chemical potential energy

Chemical Potential Energy

  • Gasoline stores energy in the same way as food stores energy: in the chemical bonds between atoms.

  • Energy stored in chemical bonds is chemical potential energy.

  • Energy is stored in the bonds that hold the carbon and hydrogen atoms together and is released when the gas is burned.

  • In this chemical reaction, chemical potential energy is released.


Gravitational potential energy

Gravitational Potential Energy

  • Anything that can fall has stored energy called gravitational potential energy.

  • Gravitational potential energy (GPE) is energy stored by objects due to their position above Earth’s surface.

  • Gravitational potential energy can be calculated from the following equation.

  • On Earth the acceleration of gravity is 9.8 m/s2, and has the symbol g.


Changing gpe

Changing GPE

  • According to the equation for gravitational potential energy, the GPE of an object can be increased by increasing its height above the ground.

  • If two objects are at the same height, then the object with the larger mass has more gravitational potential energy.


Energy 1589207

GPE

  • A 3kg crow is perched on a tree limb 20m above the ground. What is the crow’s GPE

GIVEN:

m = 3kg

h = 20m

g = 9.8 m/s2

GPE = ?

WORK:

GPE = (M)(g)(H)

GPE = 3x9.8x20

GPE = 588J


Kinetic energy

KE

V2

½ M

Kinetic Energy

  • The crow (the same as above) starts to chase a hawk and flies at a velocity of 6m/s what is his Kinetic Energy

GIVEN:

m = 3kg

v = 6 m/s

KE = ?

WORK:

KE = 1/2mxv²

KE = ½ (3kg)(6m/s)²

KE = 54 J


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