Different Forms of Energy

Chapter 3: Section 1

What is Energy?• Energy is the ability to do work (using force to move

an object) or effect change

• Measured in Joules (J)

• 1 J = 1 N x 1m

• Comes in many forms

• Energy cannot be created nor destroyed

• In an isolated system, the total amount of energy remains constant.

Types of EnergyForm of Energy Description Example of Sources

Elastic Energy Energy stored in an object due to its compression or extension

-Compressed spring-Stretched elastic

Electrical Energy Energy resulting from the movement of electrons

-Power Plant-Battery-Generator

Thermal Energy Energy resulting from the random motion of particles in a substance

-Fire-Heating element on stove-Sun

Radiation Energy Energy stored in electromagnetic waves

-Microwave-Sun-Cellphone-X-ray machines-Radio, TV

Chemical Energy Energy stored in molecular bonds

-Apple-Candle wax-Fossil fuels

Form of Energy Description Example of Sources

Wind Energy Energy resulting from the movement of air

-Wind

Sound Energy Energy contained in sound waves

-Sound-Music

Hydraulic (hydro) Energy Energy resulting from the flow of water

-waterfall-river-ocean currents

Nuclear Energy Energy stored in the nucleus of an atom

-nuclear fission (uranium)

Law of Conservation of Energy

• Energy can be transferred from one place to another.

• Energy can change form from one place to another.

Ex: In photosynthesis, plants absorb solar energy which is then transformed into chemical energy (stored in the bonds of the glucose molecule)

Our modern lifestyle depends heavily on a series of energy transfers and transformations.

Hydraulic energy Mechanical energy electrical energy thermal, light, sound, mechanical energy

Energy cannot be created nor destroyed! It can only be transferred or transformed!

Energy EfficiencyHuman beings can build machines capable of changing

energy from one form to another.

Problem: The machines can rarely convert all of the energy it consumed into a useful form.

Examples: A light bulb only converts 5% of the electrical energy

consumed into light energy. The rest is “wasted” by being converted into thermal energy, etc.

A car only uses 12% of the chemical energy in gasoline to turn the wheels of the car (mechanical energy).

Calculating Energy Efficiency

Use the equation:

Energy Efficiency = Amount of useful energy x 100 Amount of energy consumed

Example:

1. 30 Joules of energy enter a light bulb. 20 joules of energy are transformed into light. What is the energy efficiency and how much energy is dissipated as heat?

2. A kettle consumes 15 500 J of energy to boil water. It is 85 % efficient. How much energy was used by the kettle to boil water?

Try This!Some homes are still heated by hot water boiler furnaces. The components of the system are an oil tank, a furnace, water

pipes and radiators.

The furnace burns the oil from the storage tank. The heat released is used to heat water which is then pumped to radiators throughout the house. A diagram is shown below.

If all the heat from the combustion was used to heat the water, the system would be 100% efficient. However, some heat is lost in the furnace exhaust and some is lost from the pipes delivering the water to the radiators.

One litre of oil delivers 38 000 kJ of energy. 7 600 kJ are lost to the exhaust, and 1 900 kJ are lost in transporting the hot water to the radiators. Determine the efficiency of this heating system.

Thermal Energy• Results from the random movement of the particles in the

substance.• The more the particles in a solid/substance are agitated,

the more thermal energy it has.

The amount of energy within a substance depends on:

1. The temperature (the higher the temperature, the more energy)

2. The number of particles (the more particles, the more energy)

Heat- Thermal energy can be transferred from one area to another. Heat

is the amount of thermal energy that is transferred from one place to another due to a temperature difference.

- Heat always moves from warm areas to cold areas.

- A cold area indicates a lack of heat.

- Represented by the equation Q = ΔEt

where :Q = heat, measured in Joules (J)Δet = the variation in thermal energy

Heat vs. TemperatureTemperature:- Indicates how fast the particles are moving

within the substance (how much thermal energy there is).

- Measured in degrees Celsius

Heat:- The amount of thermal energy transferred from

a warm area to a cold area.- Measured in Joules

Try This!

The Relationship Between Heat, Mass, Specific Heat Capacity and Temperature Variations

• When 2 substances are heated, their temperatures increase, but not necessarily at the same rate.

Specific Heat Capacity: The amount of thermal energy required to raise the temperature of 1 gram of substance by 1 degree Celsius.

• Specific Heat Capacity is a characteristic property of matter.

• Water has a very high specific heat capacity (4.19 J/g°C)

Calculating the Heat Absorbed or Released by a given substance

Q = mcΔTWhere:Q = heat (variation in thermal energy) in Jm = mass in gc = specific heat capacity in J/g°CΔT = the change in temperature in °C

(Tf – Ti)

Interpreting your result• If your result (Q) is positive, the substance has absorbed heat.

• If your result (Q) is negative, the substance has released heat into the environment.

Try This!Examine how the thermal energy of the following

substances can vary:

1. A beaker containing 100g of water is heated from 20° to 44°C.

2. A beaker containing 100g of vegetable oil is heated from 20° to 44°C.

3. A beaker containing 200g of water is heated from 20° to 44°C.

4. A beaker containing 100g of water is cooled from 44° to 20°C.

Kinetic EnergyIt is the energy that an object possesses due to its

motion.

Depends on an objects mass and speed. (The heavier it is, the faster it moves and the more energy is has)

Ek= ½ mv2

Where:Ek = kinetic energy in J

m = mass of the object in kgv = velocity of the object in m/s

Try This!Calculate the kinetic energy of:

1. A car weighing 2500 kg traveling at 50 km/h (about 14 m/s)

2. A car weighing 2500 kg traveling at 100 km/h (about 28 m/s)

3. A minivan weighing 5000 kg traveling at 50 km/h.

Potential Energy• It is the energy reserve of an object due to its position, stress

or electric charge.

Gravitational Potential Energy:Energy reserve of an object based on its height above a

reference surface and its mass.

Ep = mgh

Where:Ep = gravitational potential energy in J

m = mass of the object in kgg = gravitational constant (9.8 N/kg at the Earth’s surface)h = height of the object above the reference surface in m

Try This!Calculate the gravitational potential energy acquired from a

rock in the following situations:

1. A 1-kg rock raised to a height of 1 m.

2. A 2-kg rock raised to a height of 1m.

3. A 1-kg rock raised to a height of 2m.

Mechanical Energy• Kinetic energy can be transformed into

potential energy and vice-versa.

• The sum of kinetic energy and the potential energy is the mechanical energy of a system.

Em = Ek + Ep

Conservation of Energy Example