Energy

What is energy? In science, energy is defined as the ability to do work. Work is done when a force makes and object move in the direction of the force applied. The tennis player does work and transfers energy to the racket. With this energy, the racket can then do work on the ball.

Law of Conservation of Energy Energy cannot be created or destroyed. Energy is transferred.

Kinetic and Potential Energy Kinetic energy is the energy of the motion. Kinetic energy= mv2/ 2 Kinetic energy is large if the object has a large mass or if it is moving fast.

Gravitational Potential Energy is the energy an object has because of its position. Gravitational potential energy depends on the object’s weight its distance from the ground. Gravitational pontential energy = weight x height

Other types of Energy Thermal Energy is the kinetic energy from the movement of the particles in an object. Chemical Energy is the energy stored in chemical bonds that hold compounds together. Electrical Energy is the energy of moving particles called electrons. Sound Energy is energy from a vibrating object. Light Energy is energy from the vibration of electrically charged particles. Nuclear Energy is the energy stored in the nucleus of an atom. Fission: two nuclei join Fusion: large nucleus splits

Wasted and Useful Energy Sankey Diagram

Useful energy transfer Many everyday objects are designed to transfer energy from one form into another useful form. What energy transfer is an electric fan designed to carry out? electrical energy kinetic energy

What is the useful energy transfer? What energy transfer is a speaker designed to carry out? electrical energy sound energy

What is the useful energy transfer? What energy transfer is a wind farm designed to carry out? Acknowledgement © Energy Northwest/DOE/NREL Turbine installation at the Nine Canyon Wind Project; largest wind farm to be built in Washington State. kinetic energy electrical energy

What is the useful energy transfer? What energy transfer is a hydroelectric power station designed to carry out? Gravitational potential energy electrical energy

Useful energy transfers Complete the input and useful output energies for the devices in this table. Device Input energy Output energy kettle solar cell catapult coal fire electrical heat light electrical elastic kinetic chemical heat

Wasted energy Whenever energy is changed from one form to another, some energy is always wasted. Energy is usually wasted as: heat energy; sound energy. All electrical devices produce a small amount of heat energy, which is normally wasted.

car engine hairdryer jet engine washing machine Wasted sound energy If you can hear a device that is not designed to make noise then energy is wasted as sound. Examples of devices that waste energy as sound include: car engine hairdryer jet engine washing machine

car engine television mobile phone charger radio Wasted heat energy If a device gets warm and it is not designed to get warm then energy is wasted as heat. Examples of devices that waste energy as heat include: car engine television mobile phone charger radio

Law of conservation of energy All energy transfers follow the law of conservation of energy: Energy cannot be created or destroyed, just changed in form. This means that energy never just ‘disappears’. The total amount of energy always stays the same, i.e. the total input energy = total output energy. In most energy transfers, the energy is transferred to several different forms, which may be useful or not useful. The energy that is transferred to unwanted forms of energy is wasted.

Energy transfer in a television An energy transfer diagram shows the input energy and the output energies for a device. This includes all the useful and wasted forms of energy. For example, in a television: light electrical sound heat

Energy transfer in a radio What are the main energy transfers in a radio? (Don’t forget the wasted energy.) sound electrical heat

Energy transfer in a car engine What are the main energy transfers in a car engine? (Don’t forget the wasted energy.) kinetic chemical sound heat

Energy efficiency Efficiency is a measure of how good a device is at changing energy from one form to another. All devices waste energy, so the efficiency of a device is never 100%. The more efficient a device is the less energy is wasted. Energy efficient light bulbs are more efficient than normal light bulbs because they w____ less energy. More of the e_______ energy that they are supplied with is converted into l____ energy and not h___. aste lectrical ight eat

Calculating efficiency The efficiency of a device can be calculated using this formula: efficiency = useful energy out total energy in Useful energy is measured in joules (J). Total energy is measured in joules (J). This means that efficiency does not have any units. It is a number between 0 and 1 or a percentage.

Efficiency

Efficiency of a bulb This filament bulb is supplied with 100 J of electrical energy which it converts to 45 J of light energy. Wasted energy = Total – Useful = 100 J – 45 J = 55 J How much energy is wasted? In what form is the energy wasted? What is the efficiency of the bulb? 55 J heat Efficiency = Useful Total = 45 J 100 J = 0.45 or 45% 0.45 or 45%

Efficiency of a radio This radio is supplied with 300J of electrical energy which it converts to 96J of sound energy. Wasted energy = Total – Useful = 300 J – 96 J = 204 J How much energy is wasted? In what form is the energy wasted? What is the efficiency of the radio? 204 J heat Efficiency = Useful Total = 96 J 300J = 0.32 or 32% 0.32 or 32%

Efficiency of a television This television converts 2 000J of electrical energy into useful energy at an efficiency of 65%. What useful energy does a television produce? How much useful energy is produced? light and sound Efficiency = Useful Total Useful = Efficiency x Total = 0.65 x 2 000 J = 1 300 J 1 300 J

Sankey Diagram Sankey diagram is used for expresing the transference of one form of energy into one or more forms. Draw a Sankey diagram with each of the problems you have solved.