Energy

Double Science Award

Note that the following is taught in year 9 however you will need it in this topic.

a) Units

4.1: use the following units: kilogram (kg), joule (J), metre (m), metre/second (m/s), metre/second² (m/s²), newton (N), second (s), watt (W)

kilogram (kg): used to measure mass

joule (J): used to measure energy

metre (m): used to measure length or distance

metre/second (m/s): used to measure speed

metre/second² (m/s²): used to measure acceleration

newton (N): used to measure mass 10N=1kg (on earth)

second (s): used to measure time

watt (W): used to measure power


b) Energy Transfer

4.2: describe energy transfers involving the following forms of energy: thermal (heat), light, electrical, sound, kinetic, chemical, nuclear and potential (elastic and gravitational)

Energy converts between the different types of energy. 

For example: 
The chemical energy in food is converted into thermal and kinetic energy.
The electrical energy in a circuit is converted into thermal and light energy if there is a light bulb.
The gravitational potential energy when at the top of a mountain is transferred into kinetic energy as an object such as a ball rolls down the mountain.
The elastic potential energy is transferred to kinetic energy in for example an elastic band.

4.3: understand that energy is conserved

Energy can never be created or destroyed, it can only be converted. 

4.4: recall and use the relationship:

efficiency = useful energy output / total energy output 

Let's try it: If 20 out of 25 joules are useful then the efficiency would be:

20J/25J

=0.8

Remember to convert it into a percentage you can do this by multiplying it by 100 and don't forget the percentage sign! So the efficiency is 80%.

Remember the efficiency is of a device is always less than 100%

4.5: describe a variety of everyday and scientific devices and situations, explaining the fate of input energy in terms of the above relationship, including their representation by Sankey diagrams

A Sankey diagram is used to show how the proportions of what the energy is converted into.

For example: Here is a Sankey diagram for a typical filament light bulb.

(credits to BBC Bitesize)

As you can see it obviously isn't a very efficient light bulb as most of the energy is being transferred into heat energy rather than light energy.

We can calculate the efficiency of the light bulb by using the equation on 4.4.

In this case, the useful energy output is light energy (10J) and the total energy output is the same amount as the electrical energy (100J). So let's substitute that into the equation:

efficiency = useful energy output / total energy output

= 10J / 100J

= 0.1

Now convert this into percentage and you get 10%, so this shows that only 10% of the energy output is useful.

Here is an energy-saving light bulb

(credits to BBC Bitesize)

As you can see this light bulb is much more efficient as there is more electrical energy being converted to light energy rather than heat energy. Let's make sure by calculating the percentage of useful energy:

efficiency = useful energy output / total energy output

= 75J / 100J

= 0.75

If you convert that into percentage by multiplying by 100 then you get 75%. The percentage of the useful energy output for the energy-saving light bulb is higher than the filament light bulb which is only 10%.

4.6: recall that energy transfer may place by conduction, convection and radiation

Conduction is the transfer of heat when particles collide and transfer the heat energy from one particle to another. It can happen in solids, liquids and gases.

Convection is when particles with heat energy rise to the top which then leads to the colder being drawn to the bottom, this creates a convection current. Convection can only happen in liquids and gases because there is not enough space for particles in a solid to move freely.

Radiation is the the transfer of energy through electromagnetic radiation (infrared waves). It doesn't need an medium and so can even happen in a vacuum. An example of radiation is from the sun, in space there is nothing so the heat and light from the sun comes to earth as radiation as it does not require a medium. Depending on the colour of the surface, an object that is shiny or light (as in colour light) the surface then reflects more rather than absorbing and emitting it. If an object is dull (not shiny) or dark coloured then the surface would absorb and emit more.

4.7: describe the role of convection in everyday phenomena

Although we can necessarily see it, convection and the effects of convection happen around us all the time. For example the wind that we feel when you go outside.

First off let's start with wind and convection currents. The sun heats the air and causes the air to rise, when heated, the air is less dense this therefore makes the air rise and the colder air that is denser to sink to the ground. This creates the wind that you may feel when you go outside. 

(credits to kids.britannica.com)

From the diagram, you can see that during the day, the land heats faster than the water, this makes the air on land heat up and rise to the top, this makes the displaced cooler air on sea sink and move to inland, this creates a cool sea breeze. At night, the water is warmer than land, therefore the air over the water heats up and rises, displacing the cooler and denser air on land, this creates a cool land breeze.

4.8: describe how insulation is used to reduce energy transfers from buildings and the human body

Insulation for buildings include: wall, floor and roof insulation. Whilst for the human body clothes are used as insulation.
All the different types of insulation used for buildings and humans contain many small holes which contain air. As you may already know, air is a bad conductor of heat as the molecules in the air are spaced out thus making it hard to conduct the heat.

c) Work and Power

4.9: recall and use the relationship between work, force and distance moved in the direction of the force:

work done= force x distance moved

W = F x d

Let's try it: If a bike travels 2km and it's driving force is 700N. The work done would be calculated like this

work done= force x distance moved

=  700N x 2km

=700N x 2000m
=1400000J

4.10: understand that work done is equal to energy transferred

As we can see from the calculation above work done is measured in joules. Therefore work done is the same as energy transferred.

Note that the following is taught in year 10 NOT in year 9.

4.11: recall and use the relationship:

gravitational potential energy = mass x g x height

GPE = m x g x h

Let's try it: If an airplane with a mass of 600kg takes off and climbs to a height of 1000m and we know that g on Earth is 10ms². The gravitational potential energy gained by the airplane would be calculated like this:

gravitational potential energy = mass x g x height

= 600kg x 10ms² x 1000m

= 6,000,000 J

4.12: recall and use the relationship:

kinetic energy = 1/2 x mass x speed²

KE = 1/2 x m v²

Let's try it: If a car with a mass of 600kg has a velocity of 28m/s. Then it's kinetic energy would be calculated like this:

kinetic energy = 1/2 x mass x speed²

= 1/2 x 600kg x 28m/s²

= 235,200 J

4.13: understand how conservation of energy produces a link between gravitational potential energy, kinetic energy and work

Solids, Liquids and Gases

Double Science Award

a) Units

5.1: use the following units: degrees Celsius (°C), kelvin (K), joule (J), kilogram (kg), Newton (N), kilogram/metre³ (kg/m³), metre (m), metre² (m²), metre³ (m³), metre/second (m/s), metre/second² (m/s²), pascal, (Pa)

degrees Celsius (°C): used to measure temperature and is based on the freezing and boiling temperature of water.

kelvin (K): 0K= −273.15 °C = absolute zero

joule (J): used to measure energy

kilogram (kg): the common scale to measure mass

Newton (N): used to measure weight 10N=1kg (on earth)

kilogram/metre³ (kg/m³): can be used to measure density

metre (m): used to measure length or distance

metre² (m²): used to measure area

metre³ (m³): used to measure volume

metre/second (m/s): used to measure speed

metre/second² (m/s²): used to measure acceleration

pascal (Pa): used to measure pressure


b) Density and Pressure

5.2: recall and use the relationship between density, mass and volume:

density=mass/volume

ρ=m/V

As you can see from above that density is measured in kg/m³, however, this is not for all cases. For example: if the mass is measured in grams and the volume is in cm³, then the density is measured in g/cm³.

5.3: describe how to determine density using direct measurements of mass and volume

Use the equation above to find out the density when you have the mass and volume.
For example: if you have a cube block and it weighs 80g and its volume is 20cm³.
Then you do:

density=mass/volume

        =80/20

          =4g/cm³

Remember that if cut the block in half, the density DOES NOT change. Also, if you double the size of the block, the density also DOES NOT change. Be careful with questions like these, they might be tricking you!

5.4: recall and use the relationship pressure, force and area:

pressure=force/area

p=F/A

E.g. If you have a blunt knife, it is harder to cut things. If you have a sharp knife, it is easier, this is because there is the same amount of force over a SMALLER area, therefore the pressure is higher. Another example is when you push on a pin with the sharp side on the surface. It is easier to push the pin into the surface (depending on the surface of course) than on the flat side to go into the surface.

Let's try it:
If you have a force of 210N and an area of 30cm². Then in order to find the pressure you do:

210N/30cm²

=7N/cm²

Then the pressure would be 7N/cm²

5.5: understand that the pressure at a point in a gas or liquid which is at rest acts equally in all directions

If you have an object in the water, you have pressure acting on the object from all directions as there are molecules bouncing off everywhere of the surface of the object.

5.6: recall and use the relationship for pressure difference

pressure difference=height x density x gravitational pull

p= h x ρ x g

An example that shows there is a pressure difference depending on the height is when you take a bucket. If you fill it with water and make holes in the bucket, you will see that the water shoots out further from the bottom of the bucket in comparison to the water from the holes at the top of the bucket. Another simple example is when you go swimming, if you go to the bottom of the pool then you feel pressure on your ears.

Let's try it:

The height of a swimming pool is 2m, the density of water is 1g/cm³, and the gravitational pull on earth 10N/kg. To calculate the pressure difference between the bottom of the pool and the middle of the pool. So you do:

For the bottom of the pool:

                                                               2m x 1g/cm³ x 10N/kg
                                                                         = 20N/cm³

Then you take the middle of the pool: 

1m x 1g/cm³ x 10N/kg
= 10N/cm³

The pressure difference is therefore:

20N/cm³ - 10N/cm³

= 10N/cm³

c) Ideal Gas Molecules

5.7: understand the significance of Brownian motion

Brownian motion is when molecules in a gas or liquid move randomly due to collisions with other molecules. It is unpredictable therefore is described as random.
It is used in many important processes in life such as diffusion (for example in plants).

5.8: recall that molecules in a gas have random motion and that they exert a force and hence a pressure on the walls of the container

Molecules in gases move randomly due to other molecules, they exert a force on the surface of the container when the molecules hit the surface. Therefore there is pressure on the walls of the container.

5.9: understand that there is an absolute zero temperature which is -273°C

Absolute zero is the temperature at which molecules have no energy therefore they stop moving. Normally, molecules in gases move quickly, molecules in liquids are irregular and are in constant motion, and finally the molecules in solids vibrate. Either way they move about, however at -273°C they stop moving.

5.10: describe the Kelvin scale of temperature and be able to convert between the Kelvin and Celsius scales

The Kelvin scale is based on the movement of molecules. -273°C = 0K. At this temperature, the molecules stop moving. To convert from celsius to Kelvin, just take the celsius and add 273 to get the kelvin. To convert Kelvin to celsius, you take the kelvin and subtract 273.

For example:

0°C = 273K

0K = -273°C

Remember that 1K DOES NOT equal 273°C, it doesn't work that way. So 10°C would equal 283K, the Kelvin scale of temperature goes up one at a time. 

For example: 

20°C = 293K

20K = -253°C

5.11: understand that an increase in temperature results in an increase in the speed of gas molecules

When you increase the temperature, it means you are increasing the heat energy that you are giving the gas. Therefore, the molecules move faster as there is more kinetic energy.

5.12: describe the qualitative relationship between pressure and Kelvin temperature for a gas in a sealed container

As the temperature increases, the pressure increases because there is more heat energy hence more kinetic energy. Due to the rise in kinetic energy, the molecules move faster and collide with the surface of the container more. This results in more force thus increasing the pressure inside the sealed container.

5.13: use the relationship between the pressure and volume of a fixed mass of gas at constant temperature

p1V1=p2V2

Basically this equation shows that if a fixed amount of gas at the same temperature as another of the same gas, the relationship between the pressure and volume would be the same.

For example: 
If the pressure of 100cm³ of air is 20N/cm², then the relationship would be the same as pressure of 200cm³ of air at 10N/cm²

Triple Award Science

Note that triple award includes the double award material as well as the additional triple award material

5.7: understand that a substance can change state from solid to liquid by the process of melting

Let's take an ice cube for example, when it melts it becomes a liquid which is water. The bonds between the molecules weaken and eventually the regular structure of the molecules breaks and it becomes irregular. The bonds are weakened due to the input of heat energy.

5.8: understand that a substance can change state from liquid to gas by the process of evaporation or boiling

When you boil water you see steam coming out of the spout of the kettle. The water changed from a liquid to a gas. When you increase the heat energy, the bonds between the molecules break and the molecules are released into the air as a gas.
The difference between boiling and evaporating is that evaporating happens all the time when the substance is a liquid. However, boiling happens at a higher temperature and needs external heat to bring the liquid to a boil.

5.9: recall that particles in a liquid have a random motion within a close-packed irregular structure

The molecules of a liquid are not fixed like a solid therefore are free to move however unlike a gas, the molecules are still close-packed. It does not form a regular structure like a solid as the bonds between the molecules are not strong enough to hold the substance together, that's why it takes the shape of it's container.
5.10: recall that particles in a solid vibrate about fixed positions within a close-packed regular structure

The molecules or particles in a solid vibrate because there is not enough room for them to move therefore they vibrate. Also, the bonds between the molecules in a solid are much stronger than in a liquid therefore it creates a close-packed regular structure.

5.16: understand that the kelvin temperature of the gas is proportional to the average kinetic energy of its molecules

As I have told you above, the Kelvin scale of temperature is based on the amount of kinetic energy in the molecules. You would understand that if you increase the heat energy given to the gas, the temperature would rise and also the amount of average kinetic energy the molecules have. On the other hand, if you decrease the amount of heat energy, then the temperature drops and the average amount of kinetic energy in its molecules is also lower.
Temperature is actually the average amount of kinetic energy in the molecules however, the energy is converted to heat energy so it can also be referred to as the measure of heat energy.

5.18: use the relationship between the pressure and Kelvin temperature of a fixed mass of gas at constant volume:

(P1/T1)=(P2/T2)

When you have a fixed amount of gas, the relationship between the pressure and Kelvin temperature is the same even if the values are different.

For example: You have 100cm³ of air, with the pressure at 10N/cm² and at 1K temperature. The relationship would be the same if the pressure was 20N/cm² and at 2K temperature.

(10N/cm² / 1K ) = ( 20N/cm² / 2K )

10 = 10

As you can see the equation shows that the relationship between the pressure and kelvin temperature of a fixed volume of gas is always the same.