Key stage 3 Physics Revision 2

Forces, Motion, Pressure, The Earth and beyond

Objective

I can:

Self assessment

before revision

Self assessment

after revision state that all the objects weigh less in water than in air explain this in terms of an upward force from the water 'cancelling out' some of the downward force of the weight

recognise that objects which float show a zero weight reading state that an object will float in water if it is less dense than water state that some liquids produce a greater upthrust on an object than others identify the forces on an object and the direction in which they are acting identify the forces which are balanced in a range of situations use arrows to scale to show situations in which forces are balanced distinguish between mass and weight record measurements of mass and weight in appropriate units describe and use the relationship between mass and weight explain differences in behaviour in terms of differences in frictional forces identify characteristics of lubricants and explain their action identify factors that might affect the frictional force between two surfaces describe examples where frictional forces are helpful explain why friction is important in the movement of vehicles identify that, for a given car, the stopping distance relates to its speed explain in words the units of speed, eg mph, km/h describe the journey shown in a speed/time graph identify, and draw representations to show, useful frictional forces and unhelpful frictional forces

recognise that in some contexts comparisons of speed can be made from measurements of time alone

compare speeds from data of distance and time identify the difference between average speed and speed at a point suggest reasons why hand-held timers may be less accurate than electronically triggered timers

give reasons why some specific measurements need to be more precise than others

give examples of movement without force, eg skating give examples of situations in which forces increase or decrease speed identify forces and show their directions state that when forces are balanced, objects do not change speed, and apply this to everyday situations

give examples of air and water resistance opposing motion explain that in order to increase speed without increasing thrust, resistance (or drag) has to be reduced

describe ways in which streamlining is achieved and why streamlining is important

describe differences in the effect of air resistance when walking or running identify that fuel consumption for a particular vehicle is greater at greater speed and relate this to air resistance

explain that increased air resistance leads to a greater heating effect explain how, at higher speeds, the movement of an object is resisted by more particles

state that as a parachute begins to descend, it speeds up and air resistance increases

explain that when air resistance balances weight, the parachute no longer speeds up

identify on a speed-time graph the point at which the upward and downward forces balance

'tell the story' of a speed-time graph and translate a description of motion into a sketched speed-time graph

explain the relationship between force and area apply the quantitative relation between pressure, force and area to a number of situations, eg skis, sharp blades

describe some effects and uses of gases under pressure apply the model of the particle theory of matter to explain the behaviour of gases under pressure

apply the particle model of matter to explain why liquids are incompressible and gases are compressible

apply the concept of transmission of pressure to predict the resulting force describe some effects and uses of liquids under pressure describe an effect of atmospheric pressure or underwater pressure describe how to make a task easier by increasing the distance between the effort and the pivot

identify levers in a number of household devices describe the arrangement of muscles on the arm and associate them with the parts of a lever

explain how an antagonistic muscle pair works describe how an object can be kept in balance, eg human body, crane apply the idea of the turning effect of a force to everyday situations recall the principle of moments and apply it to a range of situations represent the Sun, Earth and Moon by spheres and identify them in a model or diagram representing the system

use the model to explain how day and night occur, involving the Earth's rotation

use the model to explain the passing of a month and of a year use the model to explain why the Sun appears to move across the sky during a day

sequence the phases of the Moon over a 28-day period explain how the view from the Earth of the Moon causes the phases in a regular sequence

sequence a series of images showing stages of an eclipse explain, using a model and diagrams, how eclipses of the Sun and Moon occur

describe the evidence eclipses provide about the solar system describe that the axis of spin of the Earth is at an angle to the Sun identify on a diagram or model parts of the Earth which are experiencing different seasons, due to their relative position to the Sun

describe how differences in orbit and rotation time affect phenomena label a diagram showing the Sun, planets and asteroid belt and the natural satellites of the planets of the solar system

explain that the planets orbit the Sun in similar ways to the Earth, but that their orbits take different times to complete

describe how information on the planets in our solar system is obtained and used

state that within our solar system only Earth is known to support any life forms

describe the conditions necessary for life in the solar system explain that we can see the Sun and other stars because they are light sources

explain that we only see the stars at night because the Sun is much nearer to us and appears brighter

use the idea of the Earth's rotation to explain the apparent movement of the stars in the night sky

state that a ball dropped anywhere on the Earth will fall towards the centre of the planet, due to the attractive gravitational force between masses

use the idea of gravity to explain a range of observations both familiar and novel

use information provided to determine the mass and weight of objects on the Moon and other planets

show,that a rocket needs a large upward force to rise against gravity describe, eg using annotations, that the gravitational force decreases as the rocket gets further from the Earth

describe some of the landmarks of human exploration of space, describe an early model of the solar system and how it differs from our present model

argue a point of view in defence of a model of the solar system, providing evidence for their position

explain that it is the Sun's gravitational force that keeps planets in orbit state that the Moon is a natural satellite of the Earth, kept in orbit by the Earth's gravitational pull

describe some uses of artificial satellites explain why some satellites need to be in geostationary orbits describe how satellite probes provide information about the solar system and how this information is used

Key words

Use your exercise book, text books and other revision material to give definitions for the following key

words and phrases related to Forces, Motion, Pressure and The Earth and beyond.

Acceleration

Air resistance

Balanced forces

Density

Force

Friction

Geostationary

Gravity

Mass

Orbit

Pivot/Fulcrum

Pressure

Principle of moments

Satellite

Solar system

Speed

Star

Upthrust

Weight

Sample Exam Questions

The mark scheme for these questions, along with further practice questions, can be found at

http://mrblackstone.wikispaces.com/

Level 4

1. (a) Alfie made a model of part of the solar system. He used metal balls for the Sun, the Moon and the planets.

E goes around D.

B, C, D, F and G go around A.

Give the letter that is used to label:

(i) the model Sun;

..............

1 mark

(ii) the model Earth;

..............

1 mark

(iii) the model Moon;

..............

1 mark

(iv) the model planet with the largest orbit.

..............

1 mark

(b) The bar chart shows the force of gravity on eight of the planets.

(i) The gravity on Neptune is 12 N/kg.

On the chart above, draw a bar for the planet Neptune. Use a ruler.

1 mark

(ii) Give the name of a planet where you would weigh more than you weigh on Earth.

................................................................

1 mark

(iii) On which planet would a spaceship need the largest force to take off?

................................................................

1 mark

maximum 7 marks

2. The photographs below show pupils investigating the movement of objects on ramps.

Plan an investigation into the factors affecting the movement of objects on ramps.

You can use any objects and any surfaces you like, and any other equipment you need.

In the box below, write a short draft of one question you could plan to investigate about the movement of objects on ramps.

Use your draft to help you answer the following questions.

(a) Give one factor you could change as you carry out your investigation (the independent variable).

......................................................................................................................

......................................................................................................................

1 mark

(b) What factor would you observe or measure to collect your results (the dependent variable) and what equipment would you use to measure them?

The factor I would observe or measure is ......................................................

.......................................................................................................................

1 mark

The measuring equipment I would use is ......................................................

.......................................................................................................................

1 mark

(c) Give one factor you should keep the same to make your test fair.

......................................................................................................................

......................................................................................................................

1 mark

maximum 4 marks

Level 5

3. Joe saw two types of swing in the park.

He noticed that the time for one complete swing, forward and back, was different for the two types of swing.

He did not know whether the length of the chains or the mass of the person affected the time for one complete swing.

He made model swings and measured how long it took for 10 complete swings in 4 investigations.

string

plasticinemass

Here are his results.

investigation

A B C D

length of string, in cm 25 25 50 75

mass of plasticine, in g 100 50 100 100

time for 10 complete swings, in s 10.0 10.0 14.2 17.4

Here is Joe's conclusion:

Changing the mass of the plasticinehas no effect on the time takenfor 10 complete swings.

(a) Which two of his investigations, A, B, C or D, provided evidence to support his conclusion?

………………….. and …………………….

1 mark

(b) Look at the results table.

(i) Describe how the length of the string affects the time for 10 complete swings.

.............................................................................................................

.............................................................................................................

1 mark

(ii) Which three of his investigations are best evidence for this?

………………….. and …………………….and …………………….

1 mark

(c) Use his previous table of results to predict the times for 10 complete swings in two further investigations, E and F. Write your answers in the table below.

investigation

E F

length of string, in cm 25 100

mass of plasticine, in g 25 100

time for 10 complete swings, in s ................ ................

1 mark

Maximum 4 marks

4. The table below gives information about the planets of the Solar System. They are listed in alphabetical order.

planet

average distance from

the Sun in million km

diameter

in km

time for one orbit round the

Sun

time for one rotation on its axis in hours

temperature on surface of

planet in °C

Earth 150 13 000 365 days 24 +22

Jupiter 780 140 000 12 years 9.8 –150

Mars 230 6800 687 days 25 –23

Mercury 58 4900 88 days 1400 +350

Neptune 4500 51 000 165 years 16 –220

Pluto 5900 2300 248 years 150 –220

Saturn 1400 120 000 29 years 10.2 –180

Uranus 2900 51 000 84 years 17 –210

Venus 110 12 000 225 days 5800 +480

(Data obtained from The Guinness Book of Astronomy, Patrick Moore; published by Guinness 1992)

(a) Explain why Neptune and Pluto are the coldest planets.

......................................................................................................................

......................................................................................................................

1 mark

(b) Explain why there could be no liquid water on the surface of:

(i) Mars ...................................................................................................

............................................................................................................

1 mark

(ii) Venus .................................................................................................

............................................................................................................

1 mark

(c) On which planet would the time between sunrise and sunset be shortest?

..................................................................……

1 mark

(d) Which planet has the shortest year?’

1 mark

..................................................................……

(e) Give the name of the force which keeps the planets in their orbits.

..................................................................……

1 mark

Maximum 6 marks

Level 6

5. The drawing shows a boy with a bow and arrow. He is holding the arrow and pulling it back.

(a) Two horizontal forces act on the arrow. These are the force exerted by the boy’s hand and the force exerted by the string. The arrow is not moving.

The boy pulls the arrow with a force of 150 N. What is the size of the force exerted by the string on the arrow?

...................... N

1 mark

(b) When the boy lets go of the arrow, it starts to move forward.

Explain why it starts to move.

......................................................................................................................

......................................................................................................................

1 mark

(c) The arrow flies across a field and hits a target.

Two forces act on the arrow while it is in the air. Air resistance acts in the opposite direction to the movement, and gravity acts downwards. These two forces cannot balance each other, even when they are the same size. Why is this?

......................................................................................................................

......................................................................................................................

1 mark

(d) The arrow has a sharp pointed end. When the arrow hits the target, the sharp point exerts a very large pressure on the target.

Why does a sharp pointed end exert a larger pressure than a blunt end?

......................................................................................................................

......................................................................................................................

1 mark

Maximum 4 marks

6. The drawings below show Caroline diving into a swimming pool. As she falls, gravitational potential energy is changed into kinetic energy.

A

B

C

D

0.5 s

0.5 s

0.5 s

(a) Why does Caroline have no kinetic energy at A?

................................................................................................................

................................................................................................................

1 mark

(b) The table shows Caroline’s gravitational potential energy and kinetic energy at four stages of the dive.

stage of the dive total energy

(kJ)

gravitational potential energy

(kJ)

Kinetic energy (kJ)

A 8 8 0

B 8 7 1

C 8 4 4

D 8 0

(i) Write the missing kinetic energy value for stage D in the table.

(II) As Caroline falls there is no loss of energy to the air. How do the energy values for stages A, B, C and D show this?

................................................................................................................

................................................................................................................

2 marks

(c) (I) Give the name of the force that causes Caroline to speed up as she falls.

............................................................

(ii) Caroline takes 0.5 s to fall from A to B and from B to C and from C to D.

How can you tell from the drawings that she is speeding up as she falls?

................................................................................................................

................................................................................................................

2 marks

(d) When Caroline enters the water she slows down. Give the name of the force that slows her down.

..............................................................................................................1 mark

maximum 6 marks

Level 7

7. (a) The diagram below shows a car park barrier.

ironcounterweight

barrier1.5m

pivot

0.1m

50 N

(i) Calculate the turning moment produced by the barrier about the pivot. Give the unit.

.............................................................................................................

.............................................................................................................

.............................................................................................................

2 marks

(ii) The barrier is horizontal. The weight of the barrier is balanced by an iron counterweight. Calculate the downward force produced by the counterweight.

.............................................................................................................

.......................................................................................................... N

1 mark

(b) An electromagnet is placed beneath the iron counterweight as shown below.

ironcounterweight

battery

electromagnetiron core

When the switch is closed the barrier rises. Explain how the electromagnet can be used to raise the barrier.

.....................................................................................................................

.....................................................................................................................

.....................................................................................................................

.....................................................................................................................

.....................................................................................................................

2 marks

maximum 5 marks

8. The diagram shows a simple tool for punching holes in a leather belt.

pivot

base hole in base

steel peg

lightweight handle

force applied

piece of leather

not to scale

When the handle is pressed down, the steel peg presses down on the piece of leather. If the force is large enough, the peg punches through the leather, making a hole.

The diagram below shows the force applied to the handle.

pivot

steel peg

50 N

10 cm4 cm

not to scale

(a) Calculate the moment (turning effect) of the 50 N force applied to the handle. Give the units.

......................................................................................................................

......................................................................................................................

2 marks

(b) This moment makes the steel peg press down on the leather. Calculate the force with which the steel peg presses down on the leather.

......................................................................................................................

................................................................................................................... N

1 mark

(c) The next time the punch is used, the steel peg presses down on the leather with a force of 150 N.

(i) The area of the end of the steel peg is 0.1 cm2. What is the pressure of the steel peg on the leather? Give the units.

............................................................................................................

............................................................................................................

2 marks

(ii) The pressure is too small, and the punch does not go through the leather. How could you change the design of the punch to make it work using the same force on the handle?

............................................................................................................

............................................................................................................

1 mark

Maximum 6 marks

Level 8

9. A sky-diver jumped out of an aeroplane. After falling for some time she opened her parachute. The graph below shows how the speed of the sky-diver changed from the moment she jumped out of the aeroplane until she landed on the ground.

60

50

40

30

20

10

00 60 120 180 240 300 360 420

A

B

C

DE

time in seconds

speedin m/s

(a) What happened at 180 seconds and at 360 seconds after the sky-diver jumped out of the aeroplane?

180 seconds ………………………………………………………………………..

360 seconds ………………………………………………………..………………

2 marks

(b) There was an increase in air resistance on the sky-diver as her speed increased. Explain how the graph shows this.

……….………………………………………………………………………………

……….………………………………………………………………………………

1 mark

(c) Two sections of the graph show where the air resistance was equal and opposite to the sky-diver’s weight. Which sections are they?

Give the letters.

…………………… and …………………

1 mark

(d) (i) Use the graph to estimate how far the sky-diver fell between 180 s and 360 s.

…………………………………………………………………………………

…………………………………………………………………………………

1 mark

(ii) Why can this only be an approximate figure?

…………………………………………………………………………………

…………………………………………………………………………………

1 mark

Maximum 6 marks

10. (a) Two syringes are connected together as shown in the diagram below.

20 N

syringe A piston A, area = 0.5 cm

plastic tube

oil

syringe B

piston B, area = 5 cm

2

2

A force of 20 N is applied to the piston in syringe A.

(i) Calculate the pressure that the piston in syringe A exerts on the oil. Give the units.

…………………………………………………………………………………

…………………………………………………………………………………

1 mark

(ii) Calculate the force needed to just prevent the piston in syringe B from moving out. Give the unit.

…………………………………………………………………………………

…………………………………………………………………………………

1 mark

(b) The diagram below shows the brake pedal used to operate the brakes in a car. The foot applies a force of 50 N.

pivot of pedal

piston P

brake fluid

5 cm

20 cm

50 N

brake pedal

(i) Calculate the force applied to the piston P. Give the unit.

…………………………………………………………………………………

…………………………………………………………………………………

1 mark

(ii) The brake fluid pushes another piston, Q, which is attached to the car’s brakes. Piston Q has an area which is eight times larger than piston P.

Calculate the force on the car’s brakes. Give the unit.

…………………………………………………………………………………

…………………………………………………………………………………

1 mark

Maximum 4 marks