Igcse 13 Forces&Movement

8/12/2019 Igcse 13 Forces&Movement

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EDEXCEL IGCSE / CERTIFICATE IN PHYSICS 1-3

Forces and MovementEdexcel IGCSE Physics pages 23 to 33

June 17th2012

All content applies for Triple & Double Science


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Edexcel Specification

Section 1: Forces and motionc) Forces, movement, shape and momentum

understand that friction is a force that opposes motion

know and use the relationship between unbalanced force, mass and acceleration:

force = mass acceleration F = m a

know and use the relationship:weight = mass g; W = m g

describe the forces acting on falling objects and explain why falling objects reach a

terminal velocity

describe experiments to investigate the forces acting on falling objects, such as

sycamore seeds or parachutes

describe the factors affecting vehicle stopping distance including speed, mass, roadcondition and reaction time


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Force mass and acceleration

The force, mass and acceleration of anobject are related by the equation:

force =mass acceleration

F=mxa

forceis measured in N

massis measured in kg

accelerationis measured in m/s2


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also:

acceleration =

and:

mass =

m a

F

force

mass

force

acceleration


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Checking the equation


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Question 1

Calculate the force required to cause a carof mass 1200 kg to accelerate by 5 m/s2.

F=mxa

= 1200 kg x 5 m/s2Force = 6000 N


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Question 2

Calculate the acceleration produced by aforce of 200N on a mass of 4kg.

F=mxa

becomes:a=Fm

= 200N 4kg

acceleration = 50 m/s2


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Question 3

Calculate the force that accelerates a mass of300kg from rest to 6 m/s over a time of 3 seconds.

acceleration = change in velocity time

= (60)m/s 3s

acceleration= 2 m/s2

F=mxa

= 300kg x 2 m/s2

force = 600N


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Answers

F m a

24 N 4 kg 6 m/s2

200 N 40 kg 5 m/s2

600 N 30 kg 20m/s2

2 N 5 g 400 m/s2

5 N 100 g 50cm/s2

24 N

40 kg

20

2 N5000

Complete:


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Car forces

When a vehicle travels at a steady speed thefrictional forces balance the driving force.

To slow the car the engine force is reduced byreleasing the throttle and the frictional force isincreased by applying the brakes.


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Stopping a car

The total distance required to stop a car, the

stopping distance, is equal to the thinkingdistanceplus the braking distance.


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Factors affecting stopping distance

1. The reaction time of the driver

This will increase if the driver is tired, distracted orhas consumed alcohol or drugs. Increasingreaction time increases thethinking distance.

2. The speed of the carThe greater the speed the greater will be both thethinkingand brakingdistances.

Doubling the speed increases the overall stopping

distance by about four times.


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3. The mass of the car and its contents

The greater the mass the greater will be thebraking distance.

4. The condition of the road

Wet and icy roads will cause the braking distanceto increase.

5. The condition of the vehicle

Worn brakes or worn tyres will both increase thebraking distance.


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Choose appropriate words to fill in the gaps below:

When a car is moving at a _______ speed the engine force is

equal to the resistive force.

The __________ distance of a car is equal to the thinking

distance plus the _________ distance.

Tiredness, ________ and drugs are all likely to increase the

__________ distance.

A car travelling at 60 m.p.h. will require roughly ______

times stopping __________ of a car travelling at 30 m.p.h..

alcoholfour distancesteady stoppingthinking

WORD SELECTION:

braking

alcohol

four

distance

steady

stopping

thinking

braking


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Mass and weight

Mass is the amount of matter in an

object.Mass is measured in kilograms.

The mass of an object is the sameonthe Moon as on the Earth.

Weight is the force of gravity on anobject.

Weight is measured in newtons.

The weight of an object on the Moon isabout one sixththat on the Earth.

A newtonmeteris used to determine

the weightof the parcel


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The acceleration due to gravity (g)

The acceleration due to gravity (g) varies withplanet, moon and star and depends on the heightof an object.

Some examples of the acceleration due to gravity:Location m/s2 Location m/s2

Earth 10 Jupiter 24

Moon 1.6 Pluto 0.7Mars 3.7 The Sun 270


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Gravitational field strength (g)

This is an alternative way of measuring the

strength of gravity.

The gravitational field strength is equal to the

gravitational force exerted per kilogram.

Near the Earths surface, g= 10 N/kg

In most cases gravitational field strength in N/kg isnumerically equal to the acceleration due togravity in m/s2, hence they both use the samesymbol g.


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Calculating weight

weight =mass gravitational acceleration

W=m xg

weight is measured in N

massis measured in kg

gravitational acceleration is measured inm/s2

On the Earths surface amass of 1kg

has aweight of 10N.


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Falling objects

When an object falls through airor some other fluid initially theonly significant force acting on itis the downward pull of gravity.

On Earth, it will initially acceleratedownwards at 10 m/s2.


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As the object speeds up frictionalforces such as air resistancebecome greater the faster the

object moves.

Eventually the resultant force onthe object will be zero when thefrictional forces equal the weight ofthe object.

The object then moves at aconstant speed called terminalvelocity.


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Velocity-time graphs for a falling object


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Parachuting

A parachutist will have twodifferent terminal velocities.

Before opening the parachute itis about 60 m/s (140 m.p.h..).

Afterwards, due the much greaterdrag force, the terminal velocity is

about 5 m/s (12 m.p.h.)


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velocity

time

first terminalvelocity

initial

acceleration

= 10 m/s2

Velocity-time graph of a parachutist

second terminal

velocity

parachuteopened

ground

reached


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Choose appropriate words to fill in the gaps below:

Weight is the ______ of gravity on an object.

Weight is equal to the _______ of an object in kilograms

multiplied by the acceleration due to ________. Near the

Earths surface a mass of one kilogram weighs _____newtons.

When an object falls through a fluid it initially _________

because of gravity. As its ________ increases so do the

frictional forces. Eventually the frictional forces are _____ to

the weight of the object. At this stage the _________ force on

the object is zero and the object falls with its _______ velocity.

accelerates

ten

equal

speed

force

massresultant

WORD SELECTION:

gravity terminal

accelerates

ten

equal

speed

force

mass

resultant

gravity

terminal


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Online SimulationsEffect of forces on motion using a space module-

Freezeray.com

Forces in 1 Dimension- PhET - Explore the forces at

work when you try to push a filing cabinet. Create an

applied force and see the resulting friction force and total

force acting on the cabinet. Charts show the forces,

position, velocity, and acceleration vs. time. View a Free

Body Diagram of all the forces (including gravitational

and normal forces).

Motion produced by a force- linear & circular cases -

netfirmsTable Cloth & Other Newton 1st Law Demos- 'Whys

Guy' Video Clip (3 mins) (1st of 2 clips)

Inertia of a lead brick & Circular motion of a water glass -

'Whys Guy' Video Clip (3 mins) (2nd of 2 clips)

Air Track- Explore Science

Force on a Wing - Explore Science

Newton's 2nd Law ExperimentFendt

Reaction time stopping a car- also plots velocity/timegraph - NTNU

Simple gravity varying with distance and mass-Freezeway.com

Free-fall Lab - Explore ScienceGalileo Time of Fall Demonstration- 'Whys Guy' VideoClip (3 mins) - Time of fall independent of mass - Leadsslug and feather with and without air resistance. (1st of 2clips)

Distance Proportional to Time of Fall SquaredDemonstration - 'Whys Guy' Video Clip (3:30 mins) -Falling distance prortional to the time of fall squared.(2nd of 2 clips some microphone problems)

Lunar Lander- PhET - Can you avoid the boulder field

and land safely, just before your fuel runs out, as NeilArmstrong did in 1969? Our version of this classic videogame accurately simulates the real motion of the lunarlander with the correct mass, thrust, fuel consumptionrate, and lunar gravity. The real lunar lander is very hardto control.

Moonlander Use your thrusters to overcome the effectsof gravity and bring the moonlander safely down to earth.

BBC KS3 Bitesize Revision:

Weight mass and gravity

BBC AQA GCSE Bitesize Revision:Force and acceleration

F=ma

Stopping distances

Weight

Falling objects
http://www.freezeray.com/flashFiles/lander.htmhttp://phet.colorado.edu/new/simulations/sims.php?sim=Forces_in_1_Dimensionhttp://www.ngsir.netfirms.com/englishhtm/Motion.htmhttp://web.hep.uiuc.edu/home/MATS/WCIA/wcia_030226_1.wmvhttp://web.hep.uiuc.edu/home/MATS/WCIA/wcia_030226_2.wmvhttp://www.ionaphysics.org/lab/Explore/dswmedia/airtrack.htmhttp://www.ionaphysics.org/lab/Explore/dswmedia/wingforc.htmhttp://www.walter-fendt.de/ph14e/n2law.htmhttp://www.phy.ntnu.edu.tw/ntnujava/index.php?topic=387.0http://www.freezeray.com/flashFiles/gravity.htmhttp://www.ionaphysics.org/lab/Explore/dswmedia/freefall.htmhttp://web.hep.uiuc.edu/home/MATS/WCIA/wcia_030129_1.wmvhttp://web.hep.uiuc.edu/home/MATS/WCIA/wcia_030129_2.wmvhttp://web.hep.uiuc.edu/home/MATS/WCIA/wcia_030129_2.wmvhttp://phet.colorado.edu/new/simulations/sims.php?sim=Lunar_Landerhttp://www.echalk.co.uk/Science/Physics/moonLander/moonLander.htmhttp://www.bbc.co.uk/schools/ks3bitesize/science/energy_electricity_forces/forces/revise3.shtmlhttp://www.bbc.co.uk/schools/gcsebitesize/science/add_aqa/forces/forcemassrev2.shtmlhttp://www.bbc.co.uk/schools/gcsebitesize/science/add_aqa/forces/forcemassrev3.shtmlhttp://www.bbc.co.uk/schools/gcsebitesize/science/add_aqa/forces/weightfrictionrev3.shtmlhttp://www.bbc.co.uk/schools/gcsebitesize/science/add_aqa/forces/weightfrictionrev1.shtmlhttp://www.bbc.co.uk/schools/gcsebitesize/science/add_aqa/forces/weightfrictionrev2.shtmlhttp://www.bbc.co.uk/schools/gcsebitesize/science/add_aqa/forces/weightfrictionrev2.shtmlhttp://www.bbc.co.uk/schools/gcsebitesize/science/add_aqa/forces/weightfrictionrev1.shtmlhttp://www.bbc.co.uk/schools/gcsebitesize/science/add_aqa/forces/weightfrictionrev3.shtmlhttp://www.bbc.co.uk/schools/gcsebitesize/science/add_aqa/forces/forcemassrev3.shtmlhttp://www.bbc.co.uk/schools/gcsebitesize/science/add_aqa/forces/forcemassrev2.shtmlhttp://www.bbc.co.uk/schools/ks3bitesize/science/energy_electricity_forces/forces/revise3.shtmlhttp://www.echalk.co.uk/Science/Physics/moonLander/moonLander.htmhttp://phet.colorado.edu/new/simulations/sims.php?sim=Lunar_Landerhttp://web.hep.uiuc.edu/home/MATS/WCIA/wcia_030129_2.wmvhttp://web.hep.uiuc.edu/home/MATS/WCIA/wcia_030129_2.wmvhttp://web.hep.uiuc.edu/home/MATS/WCIA/wcia_030129_1.wmvhttp://www.ionaphysics.org/lab/Explore/dswmedia/freefall.htmhttp://www.ionaphysics.org/lab/Explore/dswmedia/freefall.htmhttp://www.ionaphysics.org/lab/Explore/dswmedia/freefall.htmhttp://www.freezeray.com/flashFiles/gravity.htmhttp://www.phy.ntnu.edu.tw/ntnujava/index.php?topic=387.0http://www.walter-fendt.de/ph14e/n2law.htmhttp://www.ionaphysics.org/lab/Explore/dswmedia/wingforc.htmhttp://www.ionaphysics.org/lab/Explore/dswmedia/airtrack.htmhttp://web.hep.uiuc.edu/home/MATS/WCIA/wcia_030226_2.wmvhttp://web.hep.uiuc.edu/home/MATS/WCIA/wcia_030226_1.wmvhttp://www.ngsir.netfirms.com/englishhtm/Motion.htmhttp://phet.colorado.edu/new/simulations/sims.php?sim=Forces_in_1_Dimensionhttp://www.freezeray.com/flashFiles/lander.htm


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Force and MovementNotes questions from pages 23 to 33

1. (a) State the equation relating force, acceleration and mass. (b)Calculate the acceleration that is produced by a force of 600N

acting on a mass of 120kg.

2. (a) What is weight? (b) Calculate the weight of a person of mass

90kg on the surface of (i) the Earth and (ii) the Moon.

3. (a) Give two factors in each case that would increase the (i)braking distance (ii) thinking distance of a car. (b) Give one factor

that if decreased would reduce both of the above.

4. Sketch and explain the shape of the velocity-time graph of a free-

fall parachutist from the time of leaving a plane to the time of

reaching the ground.

5. Answer the questions on pages 32 & 33.

6. Verify that you can do all of the items listed in the end of chapter

checklist on page 32.

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Igcse 13 Forces&Movement