iGCSE Coordinated Science PHYSICS UNIT 1 MOTION.pptx

PHYSICS UNIT 1 MOTION.pptx

1. Unit 1 Motion

2. >P1
Motion

All learners study some content in this chapter

IN THIS CHAPTER YOU WILL;

3. perform experiments to determine the density of an object
define speed and calculate average speed

plot and interpret distance-time and speed-time graphs

work out the distance travelled, from the area under a speed-time graph

understand that acceleration is a change in speed and the gradient of a speed-time graph

distinguish between scalar and vector quantities

define and calculate acceleration, and understand deceleration as a negative acceleration

use the gradient of a distance-time graph to calculate speed, and the gradient of a speed-time graph to calculate acceleration
discover the differences between mass and weight

describe how forces may change the size, shape and motion of a body

find the resultant of two or more forces acting along the same line

find out about the efect of tion (or air resistance or drag) on a moving object
learn how force, mass and acceleration are related

Investigate the efect of forces on a spring

describe and calculate the turning force

investigate and sopiy the princi of ments

describe the conditions needed for an object tobe in equilibrium

perform an experiment to find the centre of mass

describe how the contre of gravity ofan objec affects its stability

relate pressure to force and ares, and recall Ihe associated equation P = £

4. In pairs, either make the following measurements or describe how you would make them:
the length, width and thickness of this book, and then its volume
the thickness of a sheet of paper that makes up this book
the length of a journey (for example, on a map) that is not straight
the volume of liquid which fits into a cup, such as the one shown in Figure P1.01
the force needed to lift your school bag
which of the surfaces shown in Figure P1.02 causes more friction.

Figure P1.01: The volume of liquid in a cup can be measured.

5. SCIENCE IN CONTEXT P1.01

Around the world in 80 days

The first known circumnavigation (trip around the world) was completed by a Spanish ship on 8 September 1522. It took more
than three years. The French writer Jules Verne wrote the book Le tour du monde en quatre-vingts jours (which means Around the
World in Eighty Days) in 1873. In honour of the writer, the Jules Verne Trophy is a prize for the fastest circumnavigation by a
yacht. The award is currently held by the yacht IDEC Sport, which completed the journey in just under 41 days in 2017. In 2002,
the American Steve Fossett was the first to make a solo circumnavigation in a balloon, without stopping, taking just over 13 days.
In 2006, he flew the Virgin Atlantic GlobalFlyer the first fixed-wing aircraft to go around the world without stopping or refuelling. It
took him just under three days (Figure P1.03). Hypersonic jets are being developed that could fly at 1.7 km/s. At this speed, they
could circumnavigate the globe in an incredible six and a half hours.

6. Figure P1.03: The Virgin Atlantic GlobalFlyer passes over the Atlas Mountains.

su

Sometimes these epic adventures inspire those who do them to campaign for a better world, The British salor Ellen MacArthur is
Just such a person (Figure P1.04). She held the world record for the fastest solo circumnavigation, achieved on 7 February 2005.
However, she retired from competitive sallng to set up the Ellen MacArthur Foundation, a charity that works with businesses and in
‘education to accelerate the transition to a circular economy. A circular economy is one in which things should be designed to last a
long time and be easy to maintain, repair, reuse or recycle. Therefore, a circular economy would create less waste.

Discussion questions

고 What were the speeds of the six journeys mentioned in the first paragraph? Assume that the Earth's circumference is 40 000
km.

2 what could cause the fastest boat to not win a round-the-world yacht race?

7. Figure P1.04: Ellen MacArthur celebrates after completing her record solo round-the-world journey on 7 February 2005 in
Falmouth, England.

8. P1.01 Measuring length and volume

In physics, we make measurements of many different lengths, for example, the length of a piece of wire, the height of liquid in a tube,
the distance moved by an object, the diameter of a planet or the radius of its orbit. In the laboratory, lengths are often measured using
a ruler (such as a metre ruler).

A ruler may measure to the nearest centimetre or the nearest millimetre,

Figure P1.05 shows some things to remember when you use a ruler. The ruler is being used to measure the length of a piece of bent
wire.

VAL AL LL LL LL LL AL LL LL

Figure P1.05: Simple measurements still require careful technique, for example, finding the length of a wire.

9. —

If you have to measure a small length, such as the thickness of a wire, it may be better to measure several thicknesses and then
calculate the average. You can use the same approach when measuring something very thin, such as a sheet of paper. Take a stack of
500 sheets and measure its thickness with a ruler (Figure P1.06). Then divide by 500 to find the thickness of one sheet.

For some measurements of length, such as curved lines, it can help to lay a thread along the line. Mark the thread at either end of the
line and then lay it along a ruler to find the length. This technique can also be used for measuring the circumference of a cylindrical
object such as a wooden rod or à measuring cylinder,

Regular shaped solids
For a cube or cuboid, such as a rectangular block, measure the length, width and height of the object and multiply the measurements
together (Figure P1.07). For objects of other regular shapes, such as spheres or cylinders, you may have to make one or two
measurements and then look up the equation for the

N

10. Sem

Figure P1.07: Volume = length x width x height = 5 x 3 x 4 = 60 cm?

Liquids
For liquids, measuring cylinders can be used as shown in Figure P1.08. Remember to have your eye level with the liquid and read the
level of the bottom of the meniscus. (The meniscus is the curved surface of a liquid.) Al litre (or a 1 dma cylinder is not suitable for
measuring a small volume such as 5 cm, You will get a more accurate answer using a 10 cm? cylinder:

Irregular shaped solids

Most objects do not have a regular shape, so we cannot find their volumes simply by measuring the lengths of their sides. Here is how

to find the volume of an irregularly shaped object. This technique is known as measuring volume by displacement.

・ Select a measuring cylinder that the object will easily fit into. Portely fill with enough water to cover the object (Figure P1.09).
Note the volume of the water
Immerse the object in the water. The level of water In the cylinder wil increase, because the object pushes the water out of the
way and the only way it can move is upwards, The increase in its volume is equal to the volume of the object

12. volume
of object

object to be
measured

Figure P1.09: Measuring volume by displacement.

Units of length and volume

In physics, we generally use SI units (this is short for Le Systéme International d’Unités or The International System of Units). The SI
unit of length is the metre (m). Table P1.01 shows some alternative units of length, together with some units of volume. Note that the

litre and millilitre are not official SI units of volume, and so are not used in this book. One litre (1 1) is the same as 1 dm3, and one
millilitre (1 ml) is the same as 1 cm3.

13. Units
metre (m)

1 decimetre (dm) im

1 centimetre (cm) .01 m

1 millimetre (mm) .001 m

1 micrometre (um) 0.000 001 m
1 kilometre (km) 1000 m

[cubic metre (m?)

1 cubic centimetre (cm?) 0.000 001 m?

1 cubic decimetre (dm?) .001 m?

Table P1.01: Some units of length and volume in the SI system.

Questions

P1.01 A piece of wood has sides measuring 20 mm, 45 mm and 10 mm
a State the lengths of the sides in cm
b Calculate the volume of the block in cm.

P1.02 The volume of a piece of wood which floats in water can be measured as shown in Figure P1.10
a Write bullet points to describe the procedure.

b Find the volume of the wood.

14. steel block”

Figure P1.10: Measuring the volume of an object that floats.

P1.03 A stack of paper contains 500 sheets of paper. The stack has dimensions of 0.297 m x 21.0 cm x 50.0 mm
a What is the thickness of one sheet of paper?

b What is the volume of the stack of paper in cm??

15. P1.02 Density

‘The mass of an object Is the quantity (amount) of matter it is made of. Mass is measured in kilograms. But densi property of a
material. It tells us how concentrated its mass is.

In everyday speech, we might say that brick Is heavier than popcorn (Figure P1.11). We mean that, given equal volumes of brick and
Popcorn, the brick is heavier. In scientific terms, the density of brick is greater than the density of popcorn.

Figure P1.11: The popcorn and the brick have about the same volume, but the brick has a much bigger mass - the brick is more
‘dense than the popcorn.

Calculating density
‘We can calculate the density of a material using the equation:

ATION

16. To find the density of a material, we need to know the mass and volume of a sample of the material. The symbol for density is p, the
Greek letter rho. Density may be measured in grams per cubic centimetre (g/cm) or kilograms per cubic metre (kg/m).

A sample of ethanol has a volume of 240 cm.
Its mass is 190.0 9.
What is the density of ethanol?
Step 1: Write down what you know and what you want to know.
mass m = 190.09
volume = 240 cm?
density の
Step 2: Write down the equation for density, substitute values and calculate p.
Answer

Density of ethanol = 0.79 g/cm?

Some values of density are shown in Table P1.02. Gases have much lower densities than solids or liquids.
An object which is less dense than water will float. Ice is less dense than water, which explains why Icebergs float in the sea rather
than sinking to the bottom. Only about one-tenth of an iceberg is above the water surface. If any part of an object is above the water
surface, then it is less dense than water.

Many materials have a range of densities. Some types of wood, for example, are less dense than water and will float. Other types of
wood (such as mahogany) are more dense and will sink. The density depends on the nature of the wood (its composition).

17. [Material ¡Density / kg/m?
ar 1.29
hydrogen 0.09
helium 0.18
‘carbon dioxide [1.98
Liquids water 1000
alcohol (ethanol) 790

[Solids ice 920

mood (400-1200
lpolyethene 910-970
¡glass 2500-4200
steel 7500-8100
lead [11 340
silver 10 500
1900 19 300

Table P1.02: Densities of some substances. For gases, these are given at a temperature of 0°C and normal atmospheric pressure

515

Other types of mood (such as mahogany) are more dense and will sink. The density depends on the nature of the wood (Its
composition).

It Is useful to remember that the density of water Is 1000 kg/m, 1.0 kg/dm? or 1.0 g/cm?.

Measuring density
‘The easiest way to determine the density of a substance 15 to find the mass and volume of a sample of the substance.

18. ‘The easiest way to determine the density of a substance is to find the mass and volume of a sample of the substance.
EXPERIMENTAL SKILLS P1.01

Finding the density of an irregular shaped solid

You can determine the density of a liquid by measuring the mass of a measured volume of the liquid and using the equation:
density = mass + volume.

You will need:
* measuring cylinder
® balance

© different liquids, such as water and oil.

Getting started

You will need to place the cylinder on the balance and zero the balance before you pour in the liquid. Explain why.

19. Figure P1.12: Measuring the mass of a liquid.

Place a measuring cylinder on a balance. Set the balance to zero (Figure P1.12a).
Now pour liquid into the cylinder.

Read the volume from the scale on the cylinder (Figure P1.12b).

Read the mass from the balance.

Record your results in a table.

20. Mass of liquid / g Volume of liquid / cm? Density of liquid / g/cm?

6 Use the equation density = mass + volume to calculate the density of the liquid.
7 Repeat with other liquids.

Questions

1 List your results in order from most dense to least dense.

2 80 cm of mercury has a mass of 1080 9. Calculate the density of mercury. How does this compare to the liquids you
measured? Why is mercury an unusual liquid?

21. EXPERIMENTAL SKILLS P:

¡ding the density of a regular shaped solid

For a solid with a regular shape, you can find its volume by measurement (see Topic P1.01). Find its mass using a balance, then
calculate the density.

You will need:

* regular shaped blocks of different materials
© ruler

* balance.

Getting started

Lift the blocks and predict which materials you think will have the highest and lowest densities.
Method

1 Choose a block and record the material it is made of in a table like the one shown below.

Mater Length [width [Height [Volume

22. Measure the length, width and height of the block and use these to calculate its volume,
Use the balance to determine the mass of the block.

Use the equation density = mass + volume to calculate the density.

Repeat for other materials.

Finding the density of an irregular shaped solid

The volume of the object can be determined by the method shown in Figure PL.13, and its mass measured with a balance. The
density can then be calculated.

50 cm? of water are placed in a measuring cylinder. A stone is immersed and the level rises to 70 cm?. The mass of the stone is 52
9. What is the density of the stone?

Ex]

cee!

Figure P1.13: Method for determining the volume of an object.

23. Calculate the volume of the stone:
volume of stone = volume of stone and water- volume of water
70- 50
= Wen

2: Calculate the density of the stone

density ass + volume
52 + 20
2.6 g/em

Questions

P1.04 à An object has a mass of 100 9 and a volume of 25 em. What ss density?
b An object has a volume of 5 ma and a density of 8000 kg/m. What Is ts mass?

PLOS A brick is shown in Figure PL. It has a mass of 2.8 kg

24. Figure P1.14: A brick labelled with its dimensions.

a Give the dimensions of the brick in metres.

b Calculate the volume of the brick. Give your an two decimal places.

© Calculate the density of the brick.

A box full of 35 matches has a mass of 6.77 g. The box itself has a mass of 3.37 9
a What is the mass of one

b A match has dimensions of 42 mm x 2.3 mm x 2.3 mm. What is the volume (in cm?) of each match?

© Whatis the density of the matches?

d will the matches float or sink in water?

Forty drawing pins (thumb tacks) like those shown in Figure P1.15 g. What is the volume (in mm3)

one pin when they are made of metal with a density of 8.7 g/cm

25. Figure P1.15: A pair of drawing pins (thumb tacks).

26. P1.03 Measuring time

“The athletics coach in Figure P1.16 is using his stopwatch to time a hurdler. For a sprinter, a fraction of a second (perhaps just 0.01 5)
can make all the difference between winning and coming second or third. It is different In a marathon, where the race lasts for more
than two hours and the runners are timed to the nearest second.

Figure P1.16: An athletics coach uses a stopwatch to time a hurdler, who can then learn whether she has improved.

In the laboratory, you might need to record the temperature of a container of water every minute or find out how long an electric
current flows for. For measurements like these, Stopclocks and stopwatches can be used. You may come across two types of timing
device.

An analogue clock (Figure P1.17) is like a traditional clock whose hands move round the dlock face. You find the time by looking at
where the hands are pointing on the scale. It can be used to measure time intervals to no better than the nearest second.

27. Figure P1.17: An analogue clock.

A digital clock (Figure P1.18) or stopwatch is one that gives a direct reading of the time in numerals. For example, a digital clock
‘might show a time of 9.58 s. A digital clock records time to a precision of at least one hundredth of a second. You would never see an
analogue watch recording times in the Olympic Games.

28. Figure P1.18: A digital clock started when the gun fired and stopped 9.58 s later when Usain Bolt crossed the finishing line to win the
100 m at the 2009 World Championships in world record time.

When studying motion, you may need to measure the time taken for a rapidly moving object to move between two points. In this case,
you might use a device called a light gate connected to an electronic timer. This is similar to the way in which runners are timed in
major athletics events. An electronic timer starts when the marshal's gun is fired, and stops as the runner crosses the finishing line.

Figure P1.19 shows a typical lab pendulum. A mass, called a ,, hangs on the end of a string. The string is clamped tightly at
the top between two pieces of wood. If you pull the bob gently to one side and release it, the pendulum will swing from side to side,
The time for one of a pendulum (when it swings from left to right and back again) is called its | A single period is
usually too short a time to measure accurately. However, because a pendulum swings at a steady rate, you can use a stopwatch to
measure the time for a large number of oscillations (perhaps 20 or 50) and calculate the average time per oscillation. Any inaccuracy
in the time at which the stopwatch Is started and stopped will be much less significant if you measure the total time for a large number
of oscillations.

29. Measuring short intervals of time

Figure P1.19 shows a typical lab pendulum. A mass, called a plumb bob, hangs on the end of a string. The string is clamped tightly at
the top between two pieces of wood. If you pull the bob gently to one side and release it, the pendulum will swing from side to side.

‘The time for one oscillation of a pendulum (when it swings from left to right and back again) is called its period. A single period is
usually too short a time to measure accurately. However, because a pendulum swings at a steady rate, you can use a stopwatch to
measure the time for a large number of oscillations (perhaps 20 or 50) and calculate the average time per oscillation. Any inaccuracy
in the time at which the stopwatch is started and stopped will be much less significant if you measure the total time for a large number
of oscillations.

30. Figure P1.19: A simple pendulum

31. [Time on digital clock 7 5 [Time on analogue clock
9.87
10.34

10.01

al and analogue clocks.

CETTE) [ime for 20 osciations 72 [Time for rasematen 73
0.00 eo
020 ron
0.40 ma
seo 283
030 09
100 ws
120 aa
1.00 EZ

Table P1.04: Times for the oscilation of a pendulum.

32. In 1656, the Duteh scientist Christiaan Huygens Invented a clock based on a swinging pendulum. Clocks like these were the most
precise in the world until the 19305. One oscillation of a pendulum is defined as the time it takes for a plumb bob at the bottom of
the string to return to its original position (Figure P1.20).

Figure P1.20: One oscillation is when the plumb bob swings one way and then the other and returns to its original position.

Your task is to develop a worksheet so that students can plot a graph of how the period of oscillation of a pendulum varies with the
length of the string. They will use the graph to find the length the pendulum needs to be to give a period of one second (useful for
a clock). Your worksheet needs to:

define what an oscillation means (so that a student knows when to start and stop the stopwatch)

explain why we take the time for 10 or 20 oscillations when we only need the time for one oscillation

provide a labelled diagram of the assembled apparatus (not Just a list of equipment) so that students know how to put the

equipment together

give the method (step-by-step instructions).

33. Peer assessment
‘Swap copies of your worksheet with a classmate. Write down suggestions for any improvements on the worksheet you receive
before returning it to its owner. Note down any improvements if you have a class discussion.

Scalar and vector quantities
The measurements you have made so far in this chapter are all scalar quantities. A scalar quantity is one which has only magnitude
(size). Time, mass, energy and temperature are all examples of scalar quantities.

Some quantities that we measure in physics also have direction. For example, to fully describe a force you must give both the size of
the force and the direction it acts in. Quantities which have both size and direction are known as vector quantities. Force, weight,

acceleration and gravitational field strength are all examples of vector quantities.

In physics, the words speed and velocity have different meanings, although they are closely related: velocity is an object’s speed in a
particular stated direction (for example, 50 km/h north). Speed is a scalar quantity and velocity is a vector quantity.

34. P1.04 Understanding speed

If you travel on a major highway or through a large city, ely that someone is watching you. Cameras by the side of the road and
on overhead road signs keep an eye on traffic as it moves along. Some cameras are there to monitor the flow, so that traffic managers
can take action when blockages develop, or when accidents occur. Other cameras are equipped with sensors to spot speeding
motorists, or those who break the law at traffic lights. In some busy places, traffic police may observe the roads from helicopters.

We will look at how speed is calculated and how graphs can help us understand more about moving objects.

Distance, time and speed

Most methods to determine speed rely on making two measurements:

© he total distance travelled between two points

・ the total time taken to travel between these two points.

We can then work out the average speed between the two points.
average speed

35. We can use the equation for speed in the definition when an object is travelling at a constant speed. If it travels 10 metres in 1 second,
it will travel 20 metres in 2 seconds. Its speed is 10 m/s.

Figure P1.21: Timing a cyclist over a fixed distance. Using a stopwatch involves making judgements as to when the cyclist passes the
starting and finishing lines. This can introduce an error into the measurements. An automatic timing system might be better.

We cannot say whether it was travelling at a steady speed, or if its speed was changing. For example, you could use a stopwatch to
time a friend cycling over a fixed distance, for example, 100 metres (see Figure P1.21). Dividing distance by time would tell you their

36. average speed, but they might have been speeding up or slowing down along the way.

Table P1.05 shows the different units that may be used in calculations of speed. SI units are the standard units used in physics. The
units m/s (metres per second) should remind you that you divide a distance (in metres, m) by a time (in seconds, s) to find speed.

[distance metre, m kilometre, km
time second, s hour, h
[speed metres per second, m/s kilometres per hour, km/h

Table P1.05: Quantities, symbols and units in measurements of speed.

KED EXAMPLE P1.0

A cyclist completed a 1500 metre stage of a race in 37.5 s. What was her average speed?
Step 1: Start by writing down what you know, and what you want to know.

fance = 1500 m

time = 37.55

speed = ?

Step 2: Now write down the equation.

distance

speed =

Step 3: Substitute the values of the quantities on the right-hand side.

speed = Jo

37. 4 2

Questions

P1.10 a What was Usain Bolts average speed when he achieved his 100 m world record of 9.58 s in 20097
日 How do you know that his top speed must have been higher than this?

P1.11 A cheetah runs 100 m in 3.11 s. What Is its average speed?

P1.12 Information about three trains travelling between stations is shown in Table P1.06.

[train A 250 120
train 8 72 50
[train © 400 150

Table P1.06: Times for train journeys.

a Which train has the highest average speed?
b which train has the lowest average speed?
Rearranging the equation
Its better to remember one version of an equation and how to rearrange It than to try to remember three different versions.

38. Beware, s in this equation means distance (or displacement) and not speed. We can rearrange the equation to allow us to calculate

distance or time.
For example, a railway signaller might know how fast a train is moving, and needs to be able to predict where it will have reached a

a certain length of time:

distance = speed x time or s=vt

‘Similarly, the crew of an aircraft might want to know how long it will take for their aircraft to travel between two points on its flight

path:

A satellite is orbiting the Earth at a steady speed of 8.0 km/s (see Figure P1.22). How long will it take to complete a single orbit, «
distance of 44 000 km?