BIOLOGY Lesson 1 : Microscopes

Lesson Purpose: To describe microscopes, recall their parts, and be able to calculate magnification.

History of microscopes

A microscope is an instrument that is used to

magnify microscopic organisms and things which can’t be

seen- or seen in detail- with the naked eye. Robert Hooke

(1635 – 1703) invented the first microscope, leading to the

discovery of cells in 1665. It had a magnification of x30.

This means that the image viewed through the microscope

was 30 times bigger (x30) than the actual specimen.

It wasn’t very powerful because of the poor

quality of glass lenses used. Antonie van Leeuwenhoek

(1632-1723) invented lenses that were much better, with

fewer irregularities. His microscope had a magnification of x270. He used it to discover microorganisms in

a drop of rain water which he called ‘animacules’.

Comprehension questions

1. What is a microscope?

2. What does magnification mean?

3. State the two scientists that helped develop the early microscope.

4. Explain whose microscope was better and why?

5. What were microorganisms found in rain water called? Suggest why this was the name given to

these tiny organisms.

Development, Magnification and Units of measurements

Microscopes are described in terms of their Magnification (the number of times an image is

made larger than the object itself) and their Resolution (the smallest distance that can be seen between

two points that can be seen as two points and not blurred into each other).

The image on the right shows this effect. Both of the

letters are the same size- so the magnification is the same.

However, the letter on the right appears blurred: we can’t make

out the fine details of the specimen, because the resolution of the

image is low. A microscope (or telescope, or camera) with higher

resolution is considered better.

There are two main types of microscopes:

A light microscope uses rays of light to view specimens. It has a

magnification of up to x1500 and a resolution of 0.001mm.

An electron microscope uses beams of electrons passing through a specimen to view it. It was invented in

the 1930s. These have a magnification of up to x2,000,000 and a resolution of 0.0000002mm.

Calculating magnification

To calculate the magnification of a microscope we multiply the magnification of the two lenses (Eye piece

lens and the objective lens). So the magnification of a microscope with a x10 eyepiece lens and a x30

objective lens is 10 x 30 =300. So it has an overall magnification of x300.

Units of measurement

Millimetres (mm) are the smallest unit of measurement on a metre rule. Measurements using a

microscope are usually much smaller. Micrometres (µm), nanometres (nm) and picometres (pm) are

smaller units. In this order, these units are 1000x smaller each time. To convert between these units we

must either multiply or divide.

Example: Convert 0.01mm to µm

1mm = 1000µm

From mm µm

1 1000

= multiply by 1000

Then, 0.01mm = 0.01 x 1000 = 10µm

Comprehension questions

1. State the two types of microscopes and two differences between them.

2. Why would an electron microscope show more detail than a light microscope?

3. Calculate the magnification of a microscope with x5 eyepiece lens and x10 objective lens.

4. State the highest resolution of the electron microscope.

5. Convert the highest resolution of the electron microscope into micro-, nano- and picometers.

BIOLOGY Lesson 2: Plant and Animal Cells

Lesson Purpose: Describe plant and animal cells, their sub-cellular structures and sizes.

Discovering cells

With the development of the microscope, scientists could for the first time see what

living things were made of at the cellular level. First they could see the individual cells making up

an organism, then with stronger microscopes the parts inside the cell could be seen too. The

parts inside a cell are called the sub-cellular structures.

In 1828, a scientist called Robert Brown looked at the cells of a leaf and noticed a small

round blob in each one. He called this the cell nucleus (Latin for “inner part”). Other scientists

thought this must be a very important part of the cell, and so searched for it in animal cells. Of

course, they found that animal cells also have nuclei, and the idea that cells are the basic

building block of life came about.

Comprehension questions

1. State the scientist that discovered the nucleus in plant cells.

2. State the name for all the structures inside a cell.

3. Describe what a cell is.

4. Challenge: suggest why it was thought that the nucleus must be a very important part of

a cell.

Inside cells

Cells with a nucleus are called eukaryotic (you-carry-ottik) cells. These include plant and

animal cells. The nucleus is indeed an important part of these cells, but there are many other

parts of a cell which have since been discovered. Most animal cells have the following parts:

Cell membrane: a thin layer around the outside of the cell, which separates it from other

cells and controls what goes in and out of the cell.

Cytoplasm: a watery jelly inside the cell where most of the cell activity takes place.

Mitochondrion (plural mitochondria): shaped like a jelly bean; this is where aerobic

respiration takes place. These are so small it is very difficult to see mitochondria with a

light microscope.

Nucleus (plural nuclei): controls the cell’s activities, and contains DNA (which is bunched

up in packets called chromosomes). White blood cells have a particularly large nucleus.

Ribosomes: round structures which make new proteins, which are used to build new

parts. These are so small they cannot be seen with a light microscope.

Plant cells have the sub-cellular structures described above, but with a few additional

structures:

Cell wall: a strong wall around the outside of the cell membrane, made of cellulose. It

gives the plant cell shape, and supports and protects the cell.

Chloroplasts: sacks containing chlorophyll which traps sunlight energy for photosynthesis.

These are what make plants green.

Vacuole: a storage space in the middle of a cell for cell sap. When this is full, the plant cell

is firm. When there is not enough sap (if the plant is dehydrated), the vacuole will not be

filled, and the plant will wilt.

Discussion; What if animal cells have cell walls…?

Comprehension questions

1. List the sub-cellular structures found in most animal cells.

2. List the sub-cellular structures found in most plant cells.

3. Describe the purpose of each sub-cellular structure above in 10 words or less.

4. Explain why animal cells do not need cell walls (hint: plants don’t have skeletons).

5. Challenge: Suggest which 3 structures in a cell are the most important, and why:

a. In an animal cell;

b. In a plant cell.

Calculating and measuring cell size The magnified picture produced by a microscope is called a micrograph. If using an

electron microscope, we call the image an electron micrograph. Rulers and tape measures are

far too large to accurately measure such small structures, so in order to figure out how big a cell

is in real life, we must perform a calculation:

actual size = 𝑖𝑚𝑎𝑔𝑒 𝑠𝑖𝑧𝑒

𝑚𝑎𝑔𝑛𝑖𝑓𝑖𝑐𝑎𝑡𝑖𝑜𝑛

This is a rearrangement of the equation for working out how large an image will be under a

microscope:

image size = actual size x magnification

Similarly, if we know the actual size and the image size, we can calculate the magnification:

magnification = 𝑖𝑚𝑎𝑔𝑒 𝑠𝑖𝑧𝑒

𝑎𝑐𝑡𝑢𝑎𝑙 𝑠𝑖𝑧𝑒

Scale bars can be used to help understand how large an object is in real life too. In the

example below, the scale bar tells us that a certain distance on the image that we see is actually

much smaller in real life. Using this, we can estimate the size of a cell by working out how many

scale-bar lengths fit across the cell, or part of a cell.

The first step is to use a ruler to measure the scale bar on the image. For the human sinus

cells, the scale bar is 6mm long. The number beneath the scale bar tells us that that 6mm on the

picture is actually 10 µm in real life. So 12mm on the image would be 20 µm in real life, and 3mm

on the picture would be 5µm in real life.

Micrographs can be difficult to interpret. Usually the largest structures are the clearest,

such as the nucleus, cell wall, and the border between different cells.

Comprehension questions

1. Define “micrograph”.

2. State the equation for calculating image size from magnification and actual size.

3. State the equation for calculating magnification from the image size and actual size.

4. State what can be calculated if we know both the image size and magnification.

5. Describe how scale bars allow us to estimate the actual size of a specimen from an image

(this can be a list of steps).

6. On the onion cell micrograph above, what distance in real life is represented by 18mm on

the picture?

7. Estimate the height and width of an onion cell (in real life).

8. Estimate the size of a bacterial cell.

9. Challenge: estimate the size of the nucleus in:

a. A human sinus cell;

b. An onion cell.

BIOLOGY Lesson 3: Inside Bacteria Lesson Purpose: Describe the structure of a bacterial cell Recap Questions

1. What is a unicellular Organism?

2. What is a bacterial infection?

Subcellular Structures Bacterial cells are much smaller than plant and animal cells and it is therefore very difficult to distinguish the subcellular structures in bacteria using a light microscope. Bacteria are about 10 times smaller than animal cells. Electron microscopes can be used to provide a more detailed image which helps microbiologist to identify particular subcellular structures within bacterial cells. Chromosomal DNA of bacterial cells which are exposed to in the cytoplasm because bacterial cells do not have a nucleus. Bacterial cells also do not have mitochondria as well. Chromosomal DNA is used to control the cell. The chromosomal DNA provides instructions for ribosomes to make proteins. Bacteria cells also have circular segments of DNA which are not associated with the chromosomal DNA. These circular segments of DNA are called plasmids DNA, and plasmids can be transferred between bacterial cells through a process called conjugation. A tube, called a conjugate tube forms between two different bacterial cells, then one cell transfers a copy of plasmid DNA to another. Flagella Bacteria can have one or more flagella (singular: flagellum). These can rotate or move in a whip-like motion to move the bacterium. Bacteria cells also have one or more flagella (singular: Flagellum) that allows them to move in a whip-like motions to environments that contain more nutrients for them to absorb. It is important to note that it is not all bacteria that have flagella. The flagellum of bacteria is different from that of the sperm cell because the tail of the sperm cell is surrounded by a cell membrane but the flagellum of a bacterium is not. Bacteria cells also have a cell wall like plants to provide structure and protection. Only plant cell walls are made from cellulose. Comprehension Questions 1

1. Explain how scientists are able to identify the subcellular structures of bacterial cells.

2. Describe where DNA is stored in bacteria and what its function is?

3. What is a plasmid DNA, and how is a plasmid DNA involved in conjugation?

4. State 4 subcellular structures that bacteria share with plant and animal cells.

5. What is the difference between the structure of the tail of a sperm cell and the Flagella of

bacteria?

6. Challenge: A plasmid carried by E.coli carries a gene that provides resistance to

antimycin, an antibiotic that can be used to treat bacterial infections. Explain how this

gene can be transferred to other bacterial cells. Explain why it is important for medical

practitioners to study the DNA of Bacteria.

Properties of Bacteria Bacteria are referred to as prokaryotes because none of their sub cellular structures are surrounded by a membrane. Plant and animal cells are referred to as Eukaryotic cells because they have subcellular structures that are surrounded by a cell membrane. The size of eukaryotic cells (plant and animal cells) is mostly 5μm – 100μm, while prokaryotic cells (bacterial cell) is mostly 0.2μm – 2.0μm

Bacteria have a cell membrane which serves the same function of regulating exchange of substances. Bacteria also have a cell wall but it is not made out of cellulose, however it is made out of a substance called peptidoglycan instead. Bacterial cells do not have mitochondria so they are not able to generate as much energy as plant and animal cells. Bacterial cells are still able to perform aerobic respiration however. Animal cells and plant cells and single cell eukaryotes such as amoeba tend to build more proteins and perform more special functions so they require more energy to support their roles. Some bacteria can be found living in the gut and are thought to be beneficial to our health. Bacteria are also used largely in genetic engineering because their plasmid DNA can be manipulated and more easily introduced into their cells than animal and plant chromosomes. Comprehension Questions 2

1. What is the difference between eukaryotic cells and prokaryotic cells?

2. Describe and explain the function of the cell membrane, the cell wall and the capsule that

surrounds bacterial cells.

3. State the difference between plant cell walls and bacterial cell walls?

4. Explain why bacteria cells are used in genetic engineering.

Challenge: Evaluate the following statement. It is not important to study bacteria because people have already developed antibiotics that can kill the bacteria that are harmful to us and people have no other uses for them.

BIOLOGY Lesson 4: Transporting Substances Lesson Purpose: To describe how substances enter and leave cells. Diffusion (A)

Concentration is the scientific word for the number of particles in a given volume: at higher concentration there are more of particles in an area and at lower concentration there are few.

Diffusion is the movement of particles from an area of high concentration to an area of low concentration. This difference in concentration is called a concentration gradient and we say that particles diffuse down a concentration gradient.

Diffusion allows small particles, such as carbon dioxide, oxygen and glucose, to move across cell membranes and enter or leave cells.

Diffusion is also how smells spread from one place to another. The particles that we detect as a

smell start off in one area and are highly concentrated. As time passes they will diffuse (spread) into

areas of lower concentration, and the smell spreads.

Comprehension questions (A)

1. Define the word diffusion. [Diffusion is…, 14 words] 2. What is a concentration gradient and how do they predict the direction of diffusion? [A

concentration gradient is…, 30 words] 3. Describe and explain how smells spread from place to place. [Smells spread by…, 20 words] 4. Leaves produce oxygen. Explain why oxygen leaves leaves and goes into the air in terms of

diffusion. 5. Challenge: Diffusion allows glucose to be absorbed from our lower intestines into our blood

so it can be used to release energy in cells. Coeliac disease causes the diffusion of glucose to slow down. Suggest the symptoms of this disease and explain your answer.

Osmosis (B)

Osmosis is a special type of diffusion. Many of

the membranes (including cell membranes) in your body

are semi-permeable (or partially permeable). This means

that it is possible for some particles to penetrate the

membrane, but others will be blocked. Cell membranes

are semi-permeable and will trap large soluble molecules

whilst allowing small molecules such as water through, so

the water diffuses from high water concentration to low

water concentration. The concentration of water is higher where the concentration of solutes is lower.

Osmosis can cause cells and tissues to gain or lose mass as water enters or leaves them through

their cell membranes.

Comprehension questions (B)

1. Define the term ‘osmosis’. [Osmosis is…, 10 words] 2. What is a semi-permeable membrane? [A semi permeable membrane is…, 18 words] 3. Describe the difference between diffusion and osmosis. [Diffusion is…but…, 30 words] 4. Explain how osmosis can lead to tissues gaining or losing mass. 5. Challenge: An 8g piece of potato is left in water for an hour. Its mass increases to 8.5gExplain

this as fully as you can.

Active Transport (C)

Sometimes it is necessary for the body to

be able to carry particles across a membrane in

the opposite direction to the concentration

gradient. This can be done using active transport.

This process is used to carry solutes across the cell

membrane. A particle will become attached to a

transporter protein which is embedded in the cell

membrane. The transporter protein requires

energy to do this, so the process is said to be

active. Osmosis and diffusion do not require an

energy input, so they are passive processes.

Comprehension questions (C) 1. Define active transport. [Active transport is…, 15 words] 2. Why do we describe diffusion as being a passive process but active transport is an active

process? [Active transport is active because…whereas…, 30 words] 3. Describe how active transport moves proteins across a cell membrane. 4. Challenge: The root hair cells found in the roots of plants perform a lot of active transport.

Which organelle do you think they have more than normal numbers of, and why? Extended writing: Write a paragraph comparing and contrasting the three different types of cell transport.

PHYSICS Lesson 1: Vectors & Scalars

Lesson Purpose: To be able to distinguish between vector and scalar quantities and to explain why some

quantities are vectors and others are scalars. Vectors & Scalars (A)

When running, riding your bike or driving in a car it is common to talk about the speed at which

you are traveling. When we say ‘the car is moving at 60 mph’ we do not specify which direction it is going

in. Similarly, if you say, ‘I walked a distance of 5 km today’, you do not specify which direction you walked

in. The only information you have supplied is how long the route that you walked was. Speed and

distance are both examples of scalar quantities. The only information is how big the quantity is, not which

direction the motion took place in. A quantity that requires us to specify a direction and a size at the

same time is called a vector. All forces are vectors because when you apply a force you must indicate

which direction the force is applied in (you often do this by indicating whether the force was a push or a

pull). A vector quantity is made up of 2 different pieces of information – how big it is (called the

magnitude) and the direction the quantity points in. If we are talking about a force, we use Newtons

(shortened to N) as the unit.

Vector quantities are often shown on diagrams as arrows. The length of the arrow is proportional

to the strength of the force. The direction is shown by which way the arrow points. It is important to

remember that the difference between a vector and scalar quantity is that the vector quantity has both

direction and magnitude. A scalar quantity only has a magnitude.

Comprehension questions (A)

1. What is meant by the magnitude of a quantity? [Magnitude means…, 10 words] 2. Define a vector quantity. [A vector quantity is…, 10 words] 3. Explain the difference between a vector and a scalar quantity. [The difference between vector and

scalar quantities is…, 25 words] 4. Draw a similar diagram to the one above where the object has 3 forces acting on it (don’t forget

to make the arrows the correct length – a. 10N upwards b. 5N downwards c. 8N to the left

5. Challenge – In the previous question, what would the total force upwards be? (This is called the resultant force). Explain your answer.

Vector & Scalar Quantities (B)

Distance is an example of a scalar quantity. It measures the route taken by a moving object. The

comparable vector quantity is called displacement. This measures the difference between the starting

and finishing positions of the object. If an object ends up at its starting point, then it will have zero

displacement. The path taken has no impact on displacement.

In the same way, speed is a scalar, but velocity is a vector. To describe the velocity of an object we must

say what direction it was moving in as well as how fast it went.

Other scalar quantities include time (which only goes in one direction), mass (a quantity that all

matter has but doesn’t point anywhere), energy (which is a measure of the potential to create things like

forces) and temperature. Some other vector quantities include acceleration (the rate at which velocity

changes), weight (the force generated by gravity on an object) and momentum (the tendency of an object

to keep its motion the same as before). In each of the vector cases, we must specify the direction the

vector points in as well as how big the magnitude is.

Comprehension questions (B)

1. Describe the difference between the terms distance and displacement. [Distance is…but displacement is…, 25 words]

2. Draw a diagram like the one above that shows a journey where the displacement is zero but the distance is greater than zero. Explain what you have drawn.

3. Make a list of vector and scalar quantities with at least 4 of each. [Four scalar quantities are…, 20 words]

4. Are the following scalar or vector quantities, and why? a. Money b. The power of an engine

5. Challenge – Recall that speed = distance ÷ time. You drive 50km to visit your grandmother and then drive 50km back again. The entire trip takes you 2 hours. What was your speed over that 2 hours? Velocity is calculated in the same way, except that you use displacement instead of distance. What was your velocity over the 2 hours?

PHYSICS Lesson 2: Distance-time Graphs Lesson Purpose: Describe and interpret the shape of a distance-time graph. Recap: What unit is speed measured in, and why? Speed and its equation (A)

Speed is a scalar quantity (measures size or magnitude only). Speed is defined as the distance being

travelled by an object in a certain time. The speed of an object is calculated using the speed equation

which is stated below:

𝑆𝑝𝑒𝑒𝑑 (𝑚/𝑠) = 𝑑𝑖𝑠𝑡𝑎𝑛𝑐𝑒 (𝑚)

𝑡𝑖𝑚𝑒 (𝑠)

This equation can also be rearranged to calculate for distance or time by using the

formula triangle:

Distance =

Time =

Units for speed commonly used are metres per second (m/s), kilometres per hour (km/h) and

miles per hour (mph). In physics we tend to calculate speed in metres per second (m/s). In a journey, the

speed can increase or decrease, and so the average speed is worked out from the total distance travelled

and the total time it took. Instantaneous speed, on the other hand, is the speed at a particular moment in

the journey.

s

Speed can be measured in a laboratory by measuring the distance travelled and the time it took

to travel that distance. We use light gates- sensors which detect an object passing by- for fast moving

objects in order to get a more accurate reading than using the stopwatch.

Ex 1. A car travels 300 m in 2 minutes. Calculate its speed.

Star the target Underline values

Ex 2. How long would it take Lauren to run 100 metres if she runs at 10m/s?

s = d = t =

Copy the values s = d = t =

Convert units

Equation

Substitute values

Solve

Units

Comprehension questions (A) 1. What is speed? 2. State 3 units for measuring speed. Which one do we need to use in physics? 3. Freddie travels 200 metres in 40 seconds. What is his speed? 4. Jack tries to walk the same distance at a speed of 5m/s. How long does he take? 5. James drives at 60mph (about 100km/h) for 3 hours. How far has he gone? 6. Explain the difference between instantaneous speed and average speed. 7. Challenge: Speed can be described as the rate that distance changes with time. If we graph

distance against time, then what does the gradient of the graph represent? Remember – the gradient of a line is the rate at which y changes with respect to x (its steepness).

Describing a distance-time graph (B) A distance-time graph is a representation of a journey made on a graph. It is plotted with distance along the y-axis, and time along the x-axis. A distance-time graph can tell us various things about speed.

Horizontal lines mean the object is stationary (not moving).

Straight sloping lines mean the object is travelling at a constant speed.

The steeper the slope, the faster the object is travelling.

The speed is calculated from the gradient of the line. Comprehension questions (B)

1. What is a distance-time graph? 2. Describe the graph above in your own words in

details.

3. Sketch a distance-time graph for this journey; a car travels at 60 km/h for 2 hours on the motorway. It stops at the service station for two hours, then travels in heavy traffic at 15 km/h for 30 km.

a. Challenge: Use this graph to solve the speeds below:

4. What speed were they travelling between 0-2 hours? 5. What speed were they travelling between 2-2.5 hours? 6. What speed were they travelling 2.5-3 hours? 7. What was their average speed?

PHYSICS Lesson 3: Acceleration Lesson Purpose: To be able to define and calculate acceleration. Acceleration (A)

Acceleration is the change in an object’s velocity. In every-day language, we use the word

accelerate to mean ‘speeding up’, but since velocity is a vector – a quantity with both magnitude and

direction – acceleration can mean changing speed, changing direction or both.

Acceleration is measured in units called ‘metres per second squared’ (m/s2). These units are not

how quickly something is moving but how quickly its speed is changing. For example, when you drop an

object off a cliff, gravity accelerates it at 10 m/s2. This means that after one second it would be falling at

10 m/s, after two seconds it would be falling at 20 m/s, after three seconds it would be falling at 30 m/s

and so on.

Tasks (A):

Transform: Summarise the two paragraphs above in 15 words each. Make sure you use the following key language:

o Paragraph 1: acceleration, velocity o Paragraph 2: units, metres per second squared, m/s2

1. Explain the difference between velocity and speed. [The difference between velocity and speed…, 20 words]

2. Explain why a car travelling at a constant speed around a roundabout is considered to be accelerating. [A car travelling round a roundabout is accelerating because…, 25 words]

3. A car accelerates from standing at 4 m/s2 for 5 seconds. State how fast it is going each second and explain your answer.

4. Challenge: In drag racing, cars race in a straight line from the start to the finish line over a 400 metre course. What do you think is better for this, a car with a top speed of 40 m/s but acceleration of 10 m/s2, or one with a top speed of 100 m/s but acceleration of 5 m/s2? Explain your answer.

Acceleration calculations (B)

Acceleration can be calculated as follows:

𝑎𝑐𝑐𝑒𝑙𝑒𝑟𝑎𝑡𝑖𝑜𝑛 (𝑚/𝑠2) = 𝑐ℎ𝑎𝑛𝑔𝑒 𝑖𝑛 𝑠𝑝𝑒𝑒𝑑 (𝑚/𝑠)

𝑡𝑖𝑚𝑒 (𝑠) or 𝑎 =

𝑣−𝑢

𝑡

In the above equation ‘v’ represents the final velocity and ‘u’ represents the initial velocity so ‘v-

u’ gives us the change in velocity.

Tasks (B)

1) A lorry takes 8 s to change speed from 33 m/s to 25 m/s. What is its acceleration?

2) A drone takes 2.5 s to change speed from 18 m/s to 36 m/s. What is its acceleration?

3) A car takes 1 s to change speed from 54 m/s to 69 m/s. What is its acceleration?

4) What is the change in velocity if a drone accelerates at -8 m/s2 for 1.3 s?

5) What is the change in velocity if a rocket accelerates at 10 m/s2 for 116 s?

6) The acceleration of a rocket is -28 m/s2. How long does it take to change speed from 3557 m/s to 1905 m/s?

7) A car is travelling at 87 m/s having accelerated at 3 m/s2 for 9 s. What was its initial velocity?

8) A person is travelling at 8 m/s having accelerated at 1.4 m/s2 for 2.9 s. What was its initial velocity?

9) A cyclist travelling at 17 m/s accelerates at 4.6 m/s2 for 1 s. What is its final velocity?

PHYSICS Lesson 4: Stopping Distances Lesson Purpose: To explain how different factors affect the reaction time and stopping distance of a driver in a

motor vehicle. Stopping Distances (A)

The stopping distance of a moving vehicle is the distance that the vehicle will travel in the time it takes the

driver to a) realise that they have to stop, and b) physically stop the vehicle. The distance that the vehicle will travel

before the driver reacts to the change in situation is called the thinking distance. The vehicle will travel some

distance while it slows and stops after the brakes have been applied. This is called the braking distance. The

stopping distance is the sum of the braking distance and the thinking distance.

Comprehension questions (A) a) Why is it important for a driver to know their stopping distances? b) If the thinking distance is 5m and the breaking distance is 12m, what is the stopping distance?

Reaction Times (B)

A person’s reaction time is the time between the person detecting a stimulus (such as the sound of brakes

or the flash of a brake light) and their response (such as applying the brakes in a car). Response times are often

measured by computer. The typical visual response time is around 0.025s. However, this time can be much longer if

the person is ill, tired or has been using drugs or alcohol. Distraction, such as passengers or using a mobile phone,

can also increase reaction times.

Comprehension questions (B) c) Explain why thinking distance depends on i) the driver’s reaction time & ii) the speed of the car. d) Explain why there are legal limits on the amount of alcohol a driver is allowed to have in their bloodstream. e) Response times for driving are often measured in a driving simulator. These response times are usually

longer than those measured without the driving component. Suggest why response times might be longer in the simulator.

Braking Distances (C)

The brakes of a car or lorry use friction to slow down the vehicle. Worn brakes will mean there is less

friction and so the braking distance will be longer. Road conditions can also have a large effect on the braking

distance of a vehicle, because they affect the friction between the tires and the road. If the road is wet or the road

surface is loose then there will be less friction and the braking distance will be bigger again.

Similarly, heavy vehicles have more mass and therefore require more force to accelerate the vehicle. This

means that a heavier vehicle (such as a lorry) will require a longer distance to come to a stop than a lighter vehicle if

the same frictional force is used. As a result, lorries have greater stopping distances than cars do.

Comprehension questions (C)

f) Why are overall stopping distances greater for lorries than they are for cars? g) In some countries different speed limits are given depending on what the weather conditions are. Suggest

why it could help reduce traffic accidents to have these different speed limits? h) The stopping distances above are listed for a car containing just the driver. How would you expect these

distances to change if the car was i) carrying a whole family on holiday? ii) Was carrying boxes and furniture to help someone move house?

Extended thinking task

Make a list of all the different factors that can affect the stopping distance of a vehicle. Summarise the effect of each factor – will it affect braking distance or thinking distance?

One of the factors that affect braking distance is weather. Suggest actions a driver can take to reduce the

chance of an accident in foggy, wet or snowy conditions. Some modern vehicles have automatic systems that detect how far away the vehicle in front is and then

apply the brakes if it gets too close. Suggest advantages and disadvantages for using such an automated system in cars. Would you expect the number of accidents to change and, if so, what change would you expect?

PHYSICS Lesson 5: – Contact and non-contact forces Lesson purpose: To understand the difference between contact and non-contact forces. Contact forces Some forces are contact forces: they require direct contact between two objects. For example, when you push a door open, your hand exerts a contact force on the door. Friction is a contact force caused by two objects sliding past each other. Air and water resistance (both of which are a kind of friction) are also contact forces as because they require contact with the air or water. When you push against a hard surface – such as your weight pushing down on the floor – the surface pushes back against you with a force of the same size called the normal contact force (sometimes called the normal reaction force). Similarly when a boat’s weight pushes down on the water, an upwards force of the same size from the water, called upthrust, pushes back. Normal contact force and upthrust are also both contact forces. Forces are vectors (quantities with size and direction), so we draw them with arrows to show the direction of the force, and length of the arrow represents the size of the force. According to Newton’s 3rd law of motion, for every action force there is an equal but opposite reaction force. Similarly, my weight pushes downwards with an action force of 700 N (on a good day), and when I am standing on the floor, the floor pushes back upwards on me with a reaction normal contact force of 700 N back upwards. These pairs of forces are called action-reaction force pairs. Comprehension 1 (answers in your book in full sentences):

a) What is a contact force?

b) Give five examples of contact forces. c) What is normal contact force? d) What is an action-reaction force pair? e) A footballer kicks a ball with a force of 200 N. Sketch a diagram showing (and labelling) all

of the forces involved. f) Challenge: Why don’t you fall through the floor when your weight pushes down on it?

Give an answer in terms of forces, saying ‘because it’s hard’ is not enough.

Non-contact forces Other forces are called non-contact forces: they do not require direct contact between two objects. Gravity is an example of a contact force; you do not need to touch the Earth in order for its gravity to pull you down, as anyone who has jumped off a diving board could tell you! Other examples of non-contact forces include magnetic force and electrostatic force. Magnetic force is the force involved in magnets, and as you will know, two like poles (N-N/S-S) will repel and two opposite poles (N-S) will attract without the magnets needing to touch. Electrostatic force is the force between two electrically charged objects. Electrostatic force holds ionic bonds together, on a very small scale, and sticks a balloon charged with static electricity to the wall on a bigger scale. Objects that produce non-contact forces create areas of force around them called force fields. Anything in a force field will be affected by the force, and the further out from the source of the force, the weaker the field gets.

Magnetic fields are created by magnets magnetic field and are represented by lines of equal force pointing from north to south.

Electrostatic fields are created by objects with an electrostatic charge and can be represented by a series of arrows pointing outwards from the charged object at the centre.

Gravitational fields are created by objects with a large mass* and can be represented by a series of arrows pointing inwards towards the large object at the centre.

*Note: strictly speaking, all objects (including yourself!) produce a gravitational field, but it is only with very large objects that it is strong enough to be worth thinking about. Comprehension 2 (answers in your book in full sentences):

g) What are non-contact forces? h) Give three examples of non-contact forces. i) Sketch a diagram showing the forces involved when the

north pole of a magnet is placed near the south pole of another.

j) Sketch and label a diagram showing the forces involved when a cation (positive) is placed near an anion (negative).

k) What is a force field? Illustrate your answer with three examples.

l) Challenge: What plays a bigger role in your day-to-day life, contact forces or non-contact forces? Explain your answer.