Natural Science Grade 7 - Energy

What is CONVECTION in HEAT?

1. Convection is the transfer of energy within liquids or gases. 2. A convection current refers to the movement of a liquid or gas during energy transfer. The liquid or gas moves upwards from the heat source (as it expands) and then downwards when the liquid or gas cools (as it contracts).

What are good and bad absorbers of RADIANT HEAT?

1. Dark, matt surfaces are good absorbers of radiant heat. In other words if you are cold, wear black to absorb heat. 2. Light and shiny surfaces are poor absorbers of radiant heat. Light, shiny surfaces reflect more radiant heat than they absorb.

What 3 things make up an Energy System?

1. INPUT 2. PROCESS 3. OUTPUT

Give examples of Energy Systems?

1. Mechanical systems 2. Thermal systems 3. Electrical systems 4. Biological systems

What are good CONDUCTORS and bad CONDUCTORS of HEAT?

1. Metals are good conductors of heat. Non-metal materials are good insulators of heat. Non-metals, like plastic are bad conductors of heat and are used as insulating materials.

What is TEMPERATURE? (2 marks)

1. Temperature is a measure of how hot or cold a substance feels and it is measured in degrees Celsius (°C). 2. Temperature is a measure of the average kinetic energy of the particles in an object or system. 3. We use a thermometer to measure the temperature of an object or substance.

What happens during THERMAL ENERGY?

1. The faster the particles move in an object, the more thermal energy the object has. This is what makes it hot. 2. Particles which have more kinetic energy move faster than particles with less kinetic energy. 3. Temperature of a substance depends on the kinetic energy of the particles.

Give 3 forms of kinetic energy

1. Vibrational (the energy due to vibrational MOTION, speakers), 2. Rotational (the energy due to rotational MOTION, wheels, windmills), 3. Translational (the energy due to MOTION from one location to another).

What diagram is used to show the energy transfers in a system.

A Sankey diagram

How does Energy transfer work in a BIOLOGICAL SYTSTEM?

A plant uses the radiant (light) energy from the Sun to make its own food through the process of photosynthesis. The energy from the Sun is stored as potential energy in plants, mainly as starch. We eat the starch for potential energy.

What is LIGHT ENERGY?

A reflection/ scattering or from a light source

What happens in CONDUCTION in HEAT?

During conduction, the objects must be touching each other for energy transfer to take place.

What is a DYNAMO?

Dynamos are a type of generator that can be used to produce small amounts of electricity, such as a for a bicycle lamp.

What are some sources of Energy?

Electricity, Plants,Thermal (Heat),Fossil Fuels,HydroElectric (Water),Nuclear Energy,Solar Energy,Wind Energy

What does the Law of Conservation of Energy state?

Energy cannot be created or destroyed, only changed ( into a form which may not be useful). This means that we keep recycling all the energy in the universe all the time!

What is INPUT ENERGY?

Energy entering a system is called the input energy.

What is ELASTIC POTENTIAL ENERGY?

Energy from anything stretched or wound up, like a rubber band, it takes energy to stretch it and when you do stretch it, energy is transferred to the elastic band which will snap back.

What is Energy measured in?

Energy is measured in joules (J).

What is NUCLEAR ENERGY?

Energy that is stored in the nucleus of an atom

How does Eskom generate electricity?

Eskom uses coal powered stations and generates electricity using generators.

Give an example of WASTED ENERGY

Example: An example is a light bulb where the input is electricity and the useful output is light. However, a large amount of the energy is lost to the surroundings as thermal energy (heat from the lightbulb)

In which 3 ways does HEAT ENERGY TRANSFER happen?

Heat (energy transfer) occurs in three ways: 1. CONDUCTION 2. CONVECTION 3. RADIATION

What makes something hot/creates HEAT?

Heat is energy that is transferred from a hotter to a cooler object.

What is HEAT measured in?

Heat is measured in joules (J). This is because heat is a transfer of energy.

What is a Sankey Diagram?

In a Sankey diagram, the arrows represent the portion of the input energy which is transferred to useful energy output and the portion which is transferred to the surroundings and wasted.

Where does the national grid get its electrical energy (electricity?

In a coal power station, the coal is burned and steam is produced. The steam turns a turbine. The turbine turns a generator which produces electricity. This is transferred to the powerlines in the national grid.

What is an Energy System?

In an Energy System, energy is TRANSFORMED from one form into another. Example: Electric energy (electricity) TRANSFORMS into Kinetic Energy used to light a lightbulb.

What can we use to minimize HEAT LOSS or GAIN from a system. Like if we don't want the hot air to leave our bodies in winter?

Insulating materials. Like a thick winter jacket.

What is THERMAL ENERGY?

It is the amount of energy an object has inside of it, in other words, its internal energy.

What are the 2 Forms of Energy?

Kinetic and Potential

What is KINETIC ENERGY?

Kinetic energy is the ENERGY OF MOTION. Kinetic energy is energy which an object has because it is moving. If it's MOVING then it has kinetic energy! An object that has motion - whether it is vertical or horizontal motion - has kinetic energy. Cars, bicycles, trains, running. If it's not moving then it has no kinetic energy.

What is the NATIONAL ELECTRICITY GRID?

Like Eskom. The national electricity grid is a system in which the energy is conserved. It makes a complete circuit.

The higher a ball is, does it have more or less POTENTIAL ENERGY?

More. The higher the object (the further away from gravity) the more POTENTIAL ENERGY it has.

Do moving object have Potential or Kinetic Energy?

Moving objects also have energy, we call the energy of moving objects kinetic energy.

When you boil water is energy created?

No energy has been created, it has been transferred from the gas to the water.

What is WASTED ENERGY?

Not all of the input energy is transferred to a useful output. Some of the energy is wasted or lost.

What is POTENTIAL ENERGY?

POTENTIAL ENERGY is energy stored in an object because of its vertical position or height in a system. Like the car has the POTENTIAL to roll down the ramp.

What is ELECTRICAL ENERGY?

Particles traveling through a wire to create an electric current is electrical energy.

What is RADIATION in HEAT?

Radiation is the transfer of energy where objects do not have to be physically touching. Like the sun radiates heat. The Sun's energy is transferred to Earth by radiation.It can take place through empty space.

What is GRAVITATIONAL potential energy

Stored energy, the energy an object has because of its position. Like a ball about to drop. The higher it is the more energy it will have because of GRAVITY.

What is ENERGY TRANSFORMATION?

Takes place when energy changes from one form into another form.

What is Energy?

The ability to do work or cause change.

How is the EFFICIENCY of an energy system determined?

The efficiency of a system is determined by how much of the INPUT ENERGY is transferred to useful OUTPUT ENERGY. The GREATER the WASTED output energy, the LESS efficient the system.

What is SOUND ENERGY?

The energy from a vibrating object

What is CHEMICAL POTENTIAL ENERGY?

The energy in food and fuel and cells

What 2 variables does kinetic energy depend on? or The amount of kinetic energy an object has depends on what 2 things?

The mass (m) of the object and the speed (v) of the object.

What happens in a THERMAL ENERGY SYSTEM?

Thermal energy is transferred from one object to another.

Give examples of output energy?

Tools, appliances, vehicles and machines all provide useful energy outputs.

What happens to kinetic energy when water is boiled?

Water particles get kinetic energy from the stove or fire (the water is moving/boiling). The flame gets its energy from the gas which is being burnt. The energy in the gas is stored energy which is potential energy.

What happens to ENERGY when an animal eats a plant?

When an animal eats the plant it uses the POTENTIAL ENERGY in the FOOD which is released during respiration. This is then used by the animal to MOVE. So the potential energy in the food which the animal eats is transferred to KINETIC ENERGY. Energy has been transferred from the Sun to the plant to the animal.

Are FOSSIL Fuels burnt to generate electricity?

Yes. Fossil fuels (liek coal) are burnt to generate electricity. When fossil fuels are burnt they release greenhouse gases into the atmosphere. We need to reduce our electricity consumption in order to reduce pollution.