MODULE mod7A mod7B mod7C mod7D mod7E mod7F mod7G mod7H mod7I mod7J mod7K mod7L mod8A mod8B mod8C mod8D mod8E mod8F mod8G mod8H mod8I mod8J mod8K mod8L mod9A mod9B mod9C mod9D mod9E mod9F mod9G mod9H mod9I mod9J mod9K mod9L 9ka1
9Ka1 Investigating speed 1
Name _____________________________ Class ____________
How can you work out the speed of a toy car?
Speed is a measure of how fast things travel. To work out speed we need to know:
- how far something travels
- the time it takes.
The formula for calculating speed is: speed = distance
time
Apparatus
- Metre ruler or tape measure - Toy car
- Ramp - Blocks - Stopclock
Method
1 Set up the ramp like this:
2 Measure the height and length of the ramp. Write the numbers here:
Height _______________ cm Length _______________ cm.
3 Measure the time taken for the car to roll down the ramp and write it in the results table under Time 1.
4 Repeat the measurement twice more.
5 Repeat steps 2 to 4 with different height ramps.
Recording your results
Ramp height (cm)
Time 1 (s)
Time 2 (s)
Time 3 (s)
Mean (average) time (s)
Mean (average) speed (m/s)
Calculate the mean time for each height by adding all three results and dividing the answer by 3.
Now calculate the speed for each ramp height.
Considering your results/conclusions
Show your results on a line graph.
You need to use axes like these.
How does the height of the ramp affect the speed of the car?
_______________________________________________________________________________
Evaluation
Why do you think the timings were repeated three times?
Suggest one way to improve or extend the investigation. __________________________________
[ observing, considering, evaluating ]
9Ka2 Investigating speed 2
What factors affect the speed of a toy car?
- Metre ruler or tape measure
- Toy car or trolley
Planning
1 Which factors will have most effect on the speed of a toy car? Factors to be investigated could include: different ramp distances, different ramp heights, different surfaces.
2 Which factor will you investigate?
3 Describe how you will carry out an experiment to investigate this factor.
4 Explain how you will make your experiment a fair test.
5 To get more accurate results each timing should be repeated at least three times to find the mean (average) time.
6 Your table of results could look like this:
7 Find the mean time for each height by adding all three results and dividing the answer by 3. Use this answer to work out the speed.
8 Show your results on a line graph.
9 Write a conclusion saying which factor had the most effect on speed.
10 How could you improve your investigation?
11 How could you extend your investigation?
[ planning, observing, presenting, considering, evaluating ]
9Ka3 Measuring speed
How fast do you walk?
Complete these sentences using the words in the box. You may need to use some words more than once.
distance fast measure metres metres/second speed time
Speed is a way of saying how __________________ something is moving. To work out a speed we
need to __________________ a __________________ and a __________________ . The formula
is __________________ = distance ÷ __________________ . If the units for the distance are
__________________ , and the units for the __________________ are seconds, the units for speed
will be __________________ .
- Long tape measure - Stopclock
- Chalk - Calculator
1 Use the tape measure and chalk to mark out a distance of 10 metres.
2 Use the stop clock to find out how long it takes to walk 10 metres at your normal walking speed. Write your time in the table.
3 Now find out how long it takes if you walk 10 metres at your fastest speed. Write your time in the table.
Now calculate your walking speeds. You need to use this formula:
speed = distance
Walking
Distance (m)
Time (s)
Speed (m/s)
normal
fast
[ observing, knowledge ]
9Ka4 Ideas about speed
These statements are about speed. Some statements are true and some are false.
1 Cut out the statements and sort them into true and false statements.
2 Stick each statement into your book. Write true or false under it.
3 Explain why you think each statement is true or false.
[ knowledge ]
---------------------------------------------------------------------------------------------------------
A If I walk 2 miles in 1 hour, I am going at the same speed as someone who walks half a mile in half an hour.
B If a car travels 15 miles in half an hour, it is going at the same speed as a lorry that travels 30 miles in 1 hour.
C A cat takes 2 minutes to walk between two lamp posts. A dog takes 1 minute. The dog is walking faster than the cat.
D A car takes 2 seconds to pass a set of speed markings on the road. A bus takes 3 seconds to pass the markings because it is travelling faster than the car.
E It takes an apple 4 seconds to fall from a tree to the ground. A conker takes 6 seconds to fall. The apple was falling faster than the conker.
F A snail moves 15 cm in 2 minutes. It is moving slower than a slug, which takes 1 minute to move 8 cm.
G Jenna runs 1000 m in 6 minutes. She is running at the same speed as Danny, who runs 1500 m in 9 minutes.
H Manisha takes half an hour to walk to school. Samir takes 20 minutes, because he is walking more slowly.
9Ka5 Who was the fastest?
Athletes run races over set distances. The time they take is measured. The winner is the person who covers the distance in the shortest time. If you want to find out who was the fastest in different races, you need to calculate the speed of each athlete.
Speed is calculated using this equation:
speed = distance/time
Example
Jamie Smith ran 50 m in 6 seconds.
= 50 m/6 s
= 8.3 m/s
1 The table shows the winning times for different races. Calculate the speed for each athlete and fill in the last column.
Athlete
Race
Jamie Smith
50 m
6
8.3
Suhail Patel
1000 m
250
Jenny Baker
400 m
70
Rosie Kennett
100 m
13
Andy Groves
200 m
25
Sunita Parekh
800 m
150
2 Which athlete in question 1 was the fastest? _______________________________________
3 The Paralympics is a sporting event held for disabled athletes. Wheelchair races are run over different distances.
a Scott Jacobs won the 100 m wheelchair race in 20 seconds. How fast was he going?
______________________________________________________________________
b Sally Malin won the 200 m race in 39 seconds. How fast was she going?
c Who was the fastest, Scott or Sally?
[ numeracy ]
9Ka6 Speed, distance and time
You can remember the formula for speed using this triangle:
You can convert a speed in m/s into mph by multiplying it by 2.237.
You can convert mph to m/s by dividing by 2.237.
Show all your working when answering these questions.
1 An athlete ran 26.2 miles in 180 minutes. How fast was he running? Give your answer in miles per hour.
2 Jenny ran 100 m in 20 seconds.
a What was Jenny's speed in m/s?
b What was her speed in mph?
c How long should it take Jenny to run 5 miles? Give your answer in minutes. (Hint: 0.3 hours is not 30 minutes!)
d It actually took Jenny an hour to run 5 miles. Why was her time longer than the time you calculated in part c?
3 A car attempting to break the land speed record reached a speed of 675 mph.
a How many miles would it travel each second? (Hint: You will need to divide by the number of seconds in an hour.)
b How long would it take to travel 10 miles? Give your answer in seconds.
c How far would the car travel in 5 seconds at this speed?
4 The slowest mammal is the sloth, with an average speed of about 0.1 mph. The fastest is the cheetah, with a mean speed of 37 mph.
a What is the speed of the two animals in m/s?
b How far could the cheetah travel in 10 seconds? Give your answer in metres.
c How long would it take the sloth to travel the same distance? Give your answer in seconds.
d Approximately how many hours is your answer to part c?
9Ka7 Speed traps
The police used to measure the speed of cars on the road by having two policemen some distance apart using a stopwatch. One of them would stand and wave as a car reached him. When the wave was seen by the second policeman a stopwatch was started. As the car passed the second policeman, the stopwatch was stopped. Today the police can measure the speeds of cars using cameras. Speed cameras are found all over Britain. In fact there is an average of one speed camera for every 30 miles of road all across the country. The A40 Cheltenham to Oxford road has 19 cameras along its 40 mile length.
A speed camera uses a radar speed sensor which detects speeding cars. If the car is travelling faster than a certain speed, the camera is triggered and takes two photos of the back of the car. It takes two photos so that the speed information on the photographs can be double-checked by calculating the distance the car has moved between photos. As the photos are taken half a second apart, and there are markings on the road at fixed intervals, the speed can be calculated.
1 a The longer lines are 5 metres apart. What distance has the car travelled between the two photographs?
b What is the speed of the car in m/s?
c What is its speed in miles per hour? (You can change m/s to mph by multiplying your answer by 2.237.)
d Is the car exceeding the maximum speed limit in the UK?
2 How could the system be modified (changed) for use on a racing track? (Hint: You might need to change the spacing of the lines, or the timing of the photos.)
3 How could the system be modified for use in measuring the speed of cyclists in a race? Explain your answer.
A new system is now being used in Britain. Two cameras are set up anything from 200 metres to several kilometres apart. These cameras photograph the front of the car and are able to recognise the number plate even if it is dirty. The date, time and location of each vehicle is recorded with the number plate. When the car passes the second camera the same details are taken and the number plate matched by computer. The mean speed can then be calculated. It is no use just slowing down when you pass a camera.
4 Why is it important to control speed?
5 Why is there no advantage to the driver in slowing down as they pass a camera under the new system?
6 What are the advantages and disadvantages of the new system:
a for the police
b for motorists who like to drive fast?
[ literacy, numeracy ]
9Kb1 Investigating acceleration 1
How does changing the mass of an object change its acceleration?
Prediction
I think that a trolley with a large mass will accelerate _________________ (faster/slower) than a trolley with a small mass.
- Ramp - Blocks
- Trolley - String
- 50 g hanging mass - 0.5 kg masses
- Pulley - Stopclock
- Sticky tape
Catch the trolley before it hits the pulley at the end of the ramp.
1 Fasten the pulley to one end of your ramp, and place it near the end of the bench.
2 Put some blocks under the other end of the ramp.
3 Push the trolley gently. If it slows down and stops, put another block under the end of the ramp. If it speeds up, take a block away. You need to adjust the slope of the ramp so that the trolley just keeps moving.
4 Fasten the string to the trolley, run it over the pulley, and fasten the 50 g hanging mass to the other end.
5 Put a 0.5 kg mass on the trolley. You may need to use sticky tape to hold it on.
6 Let the mass on the string accelerate the trolley along the ramp. Time how long it takes to move along the ramp, and write the time in the results table.
7 Repeat step 6 twice more.
8 Add another 0.5 kg mass to the trolley, and repeat steps 6 and 7. Carry on adding masses and timing the trolley until you have completed the table.
Mass on trolley (kg)
Time to run along ramp (s)
Mean time to run
1st run
2nd run
3rd run
along ramp (s)
0.5
1.0
1.5
2.0
2.5
Find the mean by adding up the three results, and then dividing by 3.
I set up the ramp with a slope so that the force of _________________ cancelled out the effects of
_________________ on the trolley.
My results show that it takes _________________ (more/less) time for a trolley with a large mass
to travel along the ramp. This means that a trolley with a large mass is accelerating
_________________ (faster/slower) than a trolley with a small mass.
Why do you think you had to time the trolley with each mass three times?
Is there any way that you could improve your experiment?
9Kb2 Investigating acceleration 2
What factors affect acceleration?
You can investigate acceleration using a trolley and ramp.
1 How do you think the mass of the trolley will affect the acceleration if the force pulling the trolley is the same?
2 How do you think the force pulling the trolley will affect the acceleration if the mass of the trolley is the same?
- Pulley - Sticky tape
- Stopclock or light gates and datalogger
3 Which factors could you change?
4 Which factor will you investigate?
5 Describe how you are going to carry out your investigation. You will need to think about the following things.
- How will you compensate for the effects of friction on the trolley?
- How will you apply a force to the trolley?
- How will you make sure your test is fair? If you are going to change the force by adding masses to the end of a string, remember that those masses are accelerating as well as the trolley, so you need to keep the total mass of the trolley and masses the same.
- How will you measure the acceleration of the trolley? (Hint: You may need to measure the speed at more than one place.)
- How many times will you need to take each measurement?
- Do you need to do any preliminary experiments?
6 Show your plan to your teacher before you carry out your investigation.
7 Design a table to record your results.
8 Write a conclusion for your experiment. Have you found a relationship between mass and acceleration, or between force and acceleration?
9 How accurate and reliable are your results? Explain your answer.
10 If you had time to do your experiment again, how could you improve it?
[planning, observing, presenting, considering, evaluating ]
9Kb3 Find the forces 1
Look at the drawings of moving objects.
1 Draw arrows on each one to show the forces acting on it. Remember that the size of the arrow shows the size of the force.
2 Label the arrows. Choose the names of the forces from the words in the box.
3 Then fill in the gaps in the sentences to describe what is happening to the speed of each object. You can use each word once, more than once or not at all.
air resistance decrease force from the engine forward force from arms
forward force from hand friction gravity hand increase long
short slow down speed up stay the same upthrust water resistance
A
If the force from the engine is the same as the forces of __________________ and the speed of the
car will __________________ .
If the driver puts the brakes on, the force of __________________ will increase, and the car
will __________________.
B
The swimmer will carry on swimming at the same speed if the forward force is balanced by
__________________ .
C
There is not much __________________ between the puck and the ice. The puck will keep moving
for a __________________ time.
D
The bowler is still holding the ball. There is a force from his __________________ so the speed of
the ball will __________________ while it is still in his hand.
When the ball has left his hand its speed will __________________ because __________________
will slow it down.
E
The speed of the ball will _________________ because _________________ is slowing it down.
[knowledge ]
9Kb4 Find the forces 2
The drawings below show moving objects. For each drawing:
1 Make a simple copy of the drawing in your book. Add arrows to show the forces acting on the object. Remember that the size of the arrow represents the size of the force.
2 Label the arrows to show what is causing each force.
3 Write down any pairs of forces that are balanced.
4 Describe what is happening to the speed of the object, and explain why it is happening.
9Kb5 Top gear!
When people buy a car there are a lot of things they want to know. For some people, the amount of luggage space is the most important, or the price of the car. Other people are more interested in how fast it will go, or how quickly it will accelerate.
This table shows some information about eight different cars.
Car
Engine size (cc)
Power (bhp)*
Time to accelerate from 0-100 km/h (sec)
Mass (1000 kg)
Rover 25 1.1
1.1
74
13.5
1.00
Rover 25 1.4
1.4
83
11.8
Rover 25 1.6
1.6
107
9.5
1.01
Rover 25 1.8
1.8
115
1.05
Peugeot 406 1.8
112
12.4
1.29
Peugeot 406 2.0
137
10.8
1.33
Peugeot 406 2.2
2.2
160
9.7
Peugeot 406 3.0
3.0
210
8.1
1.45
* bhp stands for brake horse power - an old unit for measuring power.
1 a Which car in the table has the most powerful engine?
b Which car has the greatest acceleration? (Hint: the shorter the time taken to get to 100 km/h, the better the acceleration.)
2 a Look at the information for Rover cars. How does the power of the engine depend on the engine size?
b Now look at the information for Peugeot cars. Is there the same relationship between engine size and power?
c Why do you think you need to look at each make of car separately?
3 Look at the information for Peugeot cars. How does the acceleration of the car depend on engine power?
4 Look at the information for the Rover 25 1.6 and 1.8.
a Based on engine power, which car would you expect to accelerate the fastest?
b Why do you think both cars have the same acceleration?
5 If you wanted to find out if acceleration depended on engine power, would it be best to look at the information for the Rover cars or the Peugeot cars? Explain your answer.
6 The Rover 25 1.8 and the Peugeot 406 1.8 have engines with approximately the same power. Why do you think that the Peugeot does not accelerate as quickly as the Rover?
7 Find out what the 'size' of an engine refers to. (Hint: It is not the outside measurements of the engine.)
[ numeracy, research ]
9Kb6 Falling down
Why do things fall at different speeds? Many people think that heavy objects fall faster than light ones because they have more weight, but this is only part of the answer.
When Dave Scott went to the Moon on board Apollo 15 he took along a hammer and a feather. He dropped them together, and they both accelerated at exactly the same rate and hit the ground together. There was more force on the hammer, because it had more mass, but it also takes more force to accelerate a more massive object. The two effects cancel each other out, so the hammer and the feather fell at exactly the same rate.
If you tried the same experiment on Earth you would get a very different result. The hammer would fall much faster than the feather. The difference is due to air resistance. The amount of air resistance depends on an object's shape, so it is easier to work out why this happens if we think of two objects with roughly the same shape.
A balloon full of air has a mass of 10 g. Its weight is 0.1 N. A bowling ball is about the same size as the balloon, and it has a mass of 1 kg. Its weight is 10 N. (On Earth, 1 kg has a mass of 10 N.)
The effects of mass and weight cancel each other out, and both objects start to fall at the same rate. They have only just started to move, so there is no air resistance.
If you drop the balloon and the bowling ball, they will both accelerate at the same rate to start with. There is more force from gravity (weight) on the bowling ball, but because it also has more mass it only accelerates downwards at the same rate as the balloon. Once the two objects are moving, air resistance starts to act on them. If they are the same shape and moving at the same speed, the air resistance on them will be the same.
The overall downwards force on each object is now the difference between its weight and the air resistance. The air resistance is a much smaller proportion of the weight of the bowling ball, so air resistance has less effect on the speed that it falls and it falls faster than the balloon.
The balloon now only has 50% of the original downwards force on it, but the bowling ball still has 99.5% of its original force.
1 The hammer that Dave Scott dropped on the Moon had a mass of 1.32 kg.
a What was its weight on the Moon? (Gravity on the Moon is approximately 1.67 N/kg.)
b What would its mass have been on Earth?
c What would its weight have been on Earth?
2 The feather had a weight on the Moon of 0.05 N.
a What was the mass of the feather?
b What would the weight of the feather be on Earth?
3 There was more force (weight) on the hammer than the feather, so why did they both accelerate at the same rate?
4 Why would the results of this experiment be different if it was carried out in your school laboratory?
5 How could the experiment be carried out on Earth to get the same result as Dave Scott got on the Moon?
6 A football is the same size as the bowling ball described above. It has a mass of 0.5 kg.
a What is the weight of the football on Earth?
b When it has reached the same speed as the balloon and bowling ball in the second picture, what will its air resistance be? Explain how you worked out your answer.
c What will the effective downwards force on it be when it has reached this speed?
[ knowledge, numeracy ]
9Kc1 Streamlined shapes 1
Which shapes fall the fastest?
- Wallpaper paste - Measuring cylinder
- Large beaker - Plasticine
- Metre rule - Stopclock
Wash your hands after doing the experiment.
1 Divide your Plasticine into six equal pieces. Make four of the pieces into the shapes shown in the results table.
2 Invent your own shapes for the other two pieces. Draw the shapes you have made in the table.
3 Fill the measuring cylinder with wallpaper paste to near the top.
4 Drop each shape into the wallpaper paste and time how long it takes to fall. Record your results in the table.
5 Empty the wallpaper paste into the large beaker. Carefully take out your shapes and pour the wallpaper paste back into the measuring cylinder.
6 Repeat steps 4 and 5 until you have three sets of readings for each shape.
Shape
Time to fall (s)
Mean time to fall (s)
1st measurement
2nd measurement
3rd measurement
Which shape fell the fastest?________________________________________________________
Which shape had the best streamlining? _______________________________________________
Why did you need to take three sets of readings?
Was your test a fair test? Explain your answer.
How could you improve your experiment if you had time to do it again?
9Kc2 Streamlined shapes 2
Which is the best shape for streamlining?
You can drop Plasticine shapes into wallpaper paste to find out the best shape for a
streamlined object.
- Metre rule - Balance
- Stopclock
Planning and predicting
1 Which shapes will you test? Explain why you want to test these shapes.
2 Predict which shape will have the best streamlining, and explain why you think so.
3 How will you decide which shape has the best streamlining?
4 Write a method to describe how you will carry out your investigation. You need to explain:
- how you will make sure your investigation is a fair test
- what you will measure, and how you will measure it
- whether you will need to make any preliminary measurements
- how you will make sure your results are reliable.
5 Show your plan to your teacher before you start.
6 Design a table to record the results of your experiment.
7 Which shape had the best streamlining? Was your prediction correct?
8 Try to explain your results using ideas about particles.
9 Are your results reliable? Explain your answer.
10 How could you improve your experiment if you had time to do it again?
11 Are there any further investigations you could carry out to find out more about streamlining?
9Kc3 Streamlining
1 Fill in the gaps using words from the box. You may need to use some words more than once.
When the lorry is moving the forces of _____________________ and
_____________________ are trying to slow it down. A forward force from the
_____________________ is needed to keep it moving at a _____________________ speed.
Energy stored in the _____________________ is used to produce this force.
air resistance engine friction fuel steady
2 This table shows how much fuel is needed by two lorries travelling at different speeds.
Fuel needed per mile (litres)
Speed (mph)
Lorry A
Lorry B
50
0.7
0.6
55
0.8
60
65
1.2
a Plot a graph to show this information. You will need to use axes like this.
b Complete these sentences.
Both lorries use more fuel to go each mile when they are going ___________________
(faster/slower). This is because there is ___________________ (less/more) air
resistance when they are moving faster. The air resistance can be ___________________
(increased/reduced) by streamlining.
c These drawings show Lorry A and Lorry B. Complete the captions to show which one is which.
Lorry _________ . Lorry _________ .
d Explain how you worked out your answer to part c.
[ knowledge, literacy, numeracy ]
9Kc4 Fuel consumption
The table shows the fuel consumption of two different lorries when they are travelling at different speeds.
Miles travelled per litre
1.43
1.55
1.21
1.08
1.20
0.82
0.95
1 Plot a graph to show the information in the table. Put speed on the horizontal axis. Add a key to show which line refers to which lorry.
2 The engine uses energy stored in the fuel to produce a force. Why do the lorries need a force to keep them moving at a steady speed?
3 How can you tell from the information in the table that the lorries use more energy when they are travelling fast?
4 Why do the lorries use more energy when they are travelling faster?
5 Look at the pictures of the two lorries. Does lorry A belong to Daisy or Fred? Explain your answer.
6 Lorry A goes on a journey, and manages a mean speed of 50 mph. Its fuel consumption for the trip is 1.1 miles per litre. Why do you think its fuel consumption is different to the value given in the table?
7 The information in the table shows the fuel consumption when the lorries are fully loaded.
a How would the amount of energy used by the lorries change when they are empty?
b How will this affect the number of miles they can travel for each litre of fuel?
c Sketch another line on your graph to show the fuel consumption for lorry B when it is not carrying a load.
[ knowledge, presenting, numeracy ]
9Kc5 Drag coefficients
How big is the force of air resistance on a moving car? This question is important to designers, because they need to try to make the air resistance as small as possible. However, it is not a simple question to answer, because the size of the force depends on the size and shape of the vehicle, the speed it is moving, and the density of the air it is moving through. The drag force at a particular speed can be calculated using this formula:
D = × r × V2 × CD × S (You do not need to remember this formula!)
D is the drag force on the vehicle.
r is the Greek letter 'rho', and represents the density of air (about 1.225 kg/m3 at sea level).
V is the speed of the vehicle in metres per second.
CD is called the coefficient of drag. It depends on the shape of the vehicle and it is usually found by measurements in a wind tunnel. For a car, the coefficient of drag is usually between 0.4 and 0.5. Cars with good streamlined shapes have low drag coefficients.
S is the front area of the car.
1 Work out the drag force on a car at speeds from 10mph to 70mph, in 10mph intervals. Present your results in a table.
You will need to use the information above. Assume that the car has a CD of 0.45 and a front area of 2 m2. You can convert mph into m/s by dividing by 2.237.
2 Plot a graph to show the drag on the car. Put speed on the horizontal axis.
3 What causes the drag force? Use ideas about particles in your answer.
4 Why do you think the drag force on a car depends on the density of the air? Explain as fully as you can. (Hint: you need to think about what density means in terms of how many air particles there are in a particular volume of air.)
5 In some countries the land is thousands of feet above sea level, so the air density is less. Air density also decreases when the air is hot. What effect would these changes in density have on the drag force on a car? Explain your answer.
6 Sometimes people put roof racks on their cars so they can carry more luggage.
a What effect will a roof rack have on the drag force?
b Would adding a roof rack increase or decrease the drag coefficient of a car?
[ numeracy, presenting ]
9Kd1 Making a parachute
Does the size of a parachute make a difference to how fast it falls?
I think a bigger parachute will fall __________________ (faster/slower), than a small one, so it will
take a __________________ (shorter/longer) time to fall.
- Piece of plastic - 10 g mass
- Scissors - Paper clips
- Cotton thread - Calculator
1 Cut out a square 60 cm × 2 cm from a piece of plastic.
2 Cut four pieces of cotton 30 cm long, and tie a paper clip to each one.
3 Unbend the paper clips and push one through each corner of your plastic.
4 Tie the other ends of the thread to your mass. Now your parachute is ready to test.
5 Drop your parachute and time how long it takes to get to the ground. Write your result in the table below.
6 Drop the parachute twice more, then work out the mean time for your three drops. Make sure you drop it from the same height each time.
7 Repeat steps 1 to 6 for smaller parachutes. The measurements you need are in the table.
Size of
Mean time to
parachute
1st drop
2nd drop
3rd drop
fall (s)
60 cm × 60 cm
50 cm × 50 cm
40 cm × 40 cm
30 cm × 30 cm
Find the mean by adding up all three results, then divide your answer by 3.
Complete these sentences, using the words from the box.
air area resistance slower
Bigger parachutes fall ___________________ than small ones. This is because they have more
___________________ ___________________ than smaller ones. This is because they have a
bigger ___________________ .
Why do you think you had to test each parachute three times?
9Kd2 A parachute jump 1
These pictures show different stages in a parachute jump.
1 What is causing the downwards forces shown in the pictures?
2 What is causing the upwards force in pictures B to D?
3 What is causing the upwards force in picture E?
4 In which pictures is the skydiver gaining speed?
5 a Which picture shows that her air resistance has suddenly increased?
b What has caused the sudden increase in her air resistance?
c What will happen to her speed?
6 Which two pictures show balanced forces?
9Kd3 Distance-time graphs
We can show how quickly someone moves using a distance-time graph. This graph shows Jack's journey home from school.
You can see from the graph that Jack begins by running, so the first part of the graph is steep. In the second part of the graph Jack has tripped up and stopped moving, so the graph is flat. After this he walks home and the graph is not as steep as when he was running.
1 Which is:
a the flat part of the graph?
b the steepest part of the graph?
c the least steep part of the graph that is not flat?
Choose your answers from: A to B B to C C to D.
2 Copy and complete these sentences:
a The steepest part of the graph is where Jack is …
b The flattest part of the graph is where Jack is …
c The least steep part of the graph is where Jack is …
3 a Write down each section of your journey to school (for example: calling at a friend's house, walking to the bus stop).
b Sketch a distance-time graph to show your journey. Remember that the steepness of the line shows how fast you are going. Add labels to your graph to explain what is happening at each stage.
9Kd4 A parachute jump 2
This graph shows how Tom's speed changed during his parachute jump.
How speed changes with height for a skydiver.
- At point 1 Tom has just jumped out of the plane. He has only just started moving downwards, so his speed is very low and he does not have much air resistance. He is accelerating because his weight is pulling him downwards.
- At point 2 Tom is moving downwards at 40 m/s. His air resistance is increasing, because he is moving faster. His weight is still bigger than his air resistance, so he is still accelerating, but not as quickly as when he first jumped out of the plane.
1 a Is Tom still accelerating at point 3?
b How big is his air resistance compared to his weight? Explain your answer.
2 At point 4 Tom has stopped accelerating. How big is his air resistance now, compared to his weight?
3 What do you think has happened at point 5? Explain your answer.
4 a What two forces are acting on Tom at point 6?
b Which force is the biggest? Explain your answer.
c How will these forces change over the next few seconds?
5 a What is happening to Tom at point 7?
b How big is his air resistance compared to his weight?
6 What has happened at point 8?
9Kd5 Speed-time graphs
A speed-time graph can be used to show how the speed of an object changes with time. A horizontal line on the graph shows something moving at a steady speed.
1 Lorraine recorded the speed of her mum's car every minute as she was driven to school. The graph below shows her results.
a When did Lorraine's mum stop to collect a friend?
b How long did she stop for?
c For how much of the journey did the car travel at a steady speed?
d What was the fastest speed reached by the car?
e What was the total time for the journey to school?
2 It's Saturday morning, and you are going to town to meet your friends and do some shopping. You walk to your friend's house and wait until she is ready. Then you walk to the bus stop, but you have to run the last bit as the bus is just about to go. It only takes 10 minutes on the bus, then you are in town, looking into shop windows and stopping to chat to other friends you meet. When you are ready to go home you find there isn't a bus for another hour, so you decide to walk. You walk fast, as it looks as if it might start to rain soon.
Sketch a speed-time graph to show your speed during the morning. Label each section to show what it represents. (Hint: A fast walking speed is about 5 km/h.)
9Kd6 Going faster
We use many different vehicles in our everyday lives. Bicycles, cars, buses and trains are the most common ones, but you may have flown in an aeroplane if you have been abroad for a holiday, or even crossed the English Channel in a hovercraft. Most of these vehicles were invented in the last few hundred years, and some within the last 50 or 60 years. Engineers and inventors have improved the designs of vehicles, making them faster and safer.
Your task is to find out about a particular kind of vehicle and the inventor or inventors that worked on it.
You could find out about:
- George and Robert Stephenson and 'The Rocket'
- Christopher Cockerell and the hovercraft
- George Cayley, Orville and Wilbur Wright, and the development of the aeroplane
- Richard Noble and ThrustSSC
- Mike Burrows and the bicycle
- Frank Whittle, Ernst Heinkel and jet aeroplanes
- The Bell X-1 and supersonic flight.
When you have found some information, you could:
- produce an illustrated report showing the inventor and the invention
- summarise the key points about the invention
- give a short talk to the rest of the class describing what you have found out.
[ knowledge, literacy, research ]
9Kd7 Faster boats
It is much easier to go fast in an aeroplane or car than it is in a boat. The fastest aeroplane can fly at around 2200 mph, and the fastest car can travel at 716 mph. The water speed record is held by Ken Warby, who achieved a speed of just over 319 mph in his boat Spirit of Australia.
It is harder to go fast in boats because water resistance produces a much bigger drag force than air resistance. Boat designers try to have the area of hull in contact with the water as small as possible. Small, high speed boats like Spirit of Australia can plane, with most of their hull out of the water, and this reduces their water resistance. However, it takes a large engine force to make a boat plane, and this is not practical for large ships such as ferries.
Long, thin hulls have less water resistance than wide ones. However, a ship must have a certain volume of its hull in the water to allow it to float. A catamaran is a boat with two separate hulls, joined across the top. The water resistance on the two long, thin hulls is less than the water resistance would be if both hulls were combined into one.
Another way to reduce the amount of hull in the water is to use a hydrofoil. A hydrofoil is a bit like an aeroplane's wing, but underwater. When a boat fitted with a hydrofoil is not moving, it floats the same way as other boats. However, when it starts to move, the water flowing over the hydrofoil produces a lift force which lifts the boat out of the water.
1 Why is the land speed record more than twice as fast as the water speed record?
2 How do boat designers try to reduce water resistance?
3 a What is planing?
b Why don't large ships like passenger liners plane?
4 a What is a catamaran?
b Why can catamarans go faster than normal boats?
c Can you think of any disadvantages of using a catamaran instead of an ordinary boat? (Hint: Think about carrying cargo.)
5 a What is a hydrofoil?
b How does a hydrofoil allow a boat to go faster?
c Hydrofoils are only used on fairly small ferries. Why do you think they are not used on larger ships?
6 Find out what a trimaran is.
[ literacy, knowledge, research ]
9K Summary Sheets
Speeding up
Calculating speed
Speed tells us how fast something is going.
We can work out the mean (average) speed of something by using this formula:
mean speed = distance travelled ÷ time taken.
Speed can be measured in:
- metres per second (m/s)
- kilometres per hour (km/h)
- miles per hour (mph).
We can show how things move on a distance-time graph. This graph shows Kieron walking to school.
Forces
Balanced forces are forces which are the same size but work in opposite directions. Unbalanced forces make things change speed, change shape or change direction.
If forces are balanced:
- a stationary object stays stationary
- a moving object continues to move at the same speed.
If forces are unbalanced:
- a stationary object will start to move
- a moving object will change its speed or direction.
The motorbike is accelerating because the forward force is greater than the backward force.
The motorbike is going at a steady speed. The forces are balanced.
A car or motorbike uses fuel to move at a steady speed because it needs a force from the engine to balance the forces of air resistance and friction.
The amount of air resistance on something can be reduced by giving it a smooth, streamlined shape. The air resistance increases as the speed increases, so cars use up more fuel per mile when they are travelling fast. Air resistance is caused by air particles hitting the moving object. The particles transfer energy to the object, which is why objects moving through air can get hot.
The forces on a skydiver change during a jump. Her weight is the same all the time, but her air resistance changes during the jump. We can use a speed-time graph to show what happens.
- At A she has just jumped out of the plane so she has only just started to move downwards. Her air resistance is very small.
- At B her air resistance is bigger, but not as big as her weight so she is still gaining speed.
- At C the forces on her are balanced so she falls at a steady speed.
- At D she has opened her parachute. The air resistance force is suddenly a lot bigger than her weight, so she slows down.
- At E the forces are balanced again, and she will continue to fall at a steady speed until she reaches the ground.
9K Target Sheet
Topic
Targets
Before the unit
I have learned this
I have revised this
9Ka
1
Know what is meant by speed.
2
Know how to calculate speed.
3
Know what mean speed means.
4
Be able to rearrange the speed formula.
9Kb
Know the effects of balanced forces on a moving object.
Know the effects of unbalanced forces on a moving object.
Be able to identify the forces on objects.
Know the factors that affect acceleration.
9Kc
Know how air resistance can be reduced.
Know about the effect of speed on air resistance.
Know why a car needs to use energy to move at a steady speed.
Know what causes air resistance.
9Kd
Know how the forces on a skydiver change during a jump.
Know why skydivers reach a maximum speed.
Know how to interpret distance-time graphs.
Know how to interpret speed-time graphs.
9K Word Sheets
Word sheets that include new words from the 'Focus on:' pages are available on the Exploring Science website.
9Ka - The need for speed
Word
Pronunciation
Meaning
mean speed
The total distance something travels divided by the total time taken allows you to calculate the thing's mean or average speed.
speed
How fast something is moving. Often measured in metres per second (m/s), miles per hour (mph) or kilometres per hour (km/h).
9Kb - Faster and faster
accelerate
ack-sell-er-ate
Change speed.
air resistance
A force that tries to slow down things that are moving through the air. It is a type of friction.
balanced forces
When two forces are the same strength, but working in opposite directions.
friction
A force that tries to slow things down when two things rub against each other.
unbalanced forces
When two forces working in opposite directions are not the same strength.
9Kc - Drag act
drag
Another name for air resistance or water resistance.
streamlined
Giving something a smooth shape to reduce the air resistance or water resistance.
water resistance
A force that tries to slow down things that are moving through water. It is a type of friction.
9Kd - Hitting the limit
distance-time graph
A graph that shows how far something has moved in a certain time.
terminal velocity
The maximum speed of an object. Usually only applies to falling objects when the downward force is balanced by drag.