forces powerpoint revision - Island Physicsislandphysics.wdfiles.com/local--files/igcse/forces.ppt · PPT file · Web viewForces Revision Syllabus Motion Forces * Boardworks GCSE

Stopwatch Graph Home

Forces RevisionSyllabusMotionForces


Syllabus: Movement and position use the following units: kilogram (kg), metre (m),

metre/second (m/s), metre/second2 (m/s2), newton (N), second (s) (P1.1).

understand and use distance–time graphs (P1.2) recall and use the relationship between average speed,

distance moved and time average speed = distance moved / time taken (P1.3) recall and use the relationship between acceleration, velocity

and time acceleration = change in velocity / time taken a = (v-u)/t (P1.4) interpret velocity–time graphs (P1.5) determine acceleration from the gradient of a velocity–time

graph and the distance travelled from the area between the graph and the time axis (P1.6).


Syllabus Double Award express a force as a push or pull of one body on another identify various types of force (e.g. gravitational, electrostatic, etc.) understand that friction is a force that opposes motion recall and use the relationship between unbalanced force, mass and

acceleration: force = mass × acceleration F = m × a recall and use the relationship between weight, mass and g : weight = mass × g W = m × g describe the forces acting on falling objects and explain why falling

objects reach a terminal velocity describe the factors affecting vehicle stopping distance including

speed, mass, road condition and reaction time recall and use the relationship between the moment of a force and its

distance from the pivot: moment = force × perpendicular distance from pivot recall that the weight of a body acts through its centre of gravity describe how extension varies with applied force for helical springs,

metal wires and rubber bands recall that the initial linear region of a force – extension graph is

associated with Hooke’s law


Syllabus Separate Science express a force as a push or pull of one body on another identify various types of force (e.g.

gravitational, electrostatic etc) distinguish between vector and scalar quantities appreciate the vector nature of a force add forces that act along a line understand that friction is a force that opposes motion recall and use the relationship between unbalanced force, mass and acceleration

force = mass × acceleration F = m × a

recall and use the relationship between weight, mass and g : weight = mass × g W = m × g

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

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

recall and use the relationship between the moment of a force and its distance from the pivot: moment = force × perpendicular distance from pivot

recall that the weight of a body acts through its centre of gravity recall and use the principle of moments for a simple system of parallel forces acting in one plane understand that the upward forces on a light beam supported at its ends vary with the position of

a heavy object placed on the beam describe how extension varies with applied force for helical springs, metal wires and rubber bands recall that the initial linear region of a force - extension graph is associated with Hooke’s law


Motion


Speed vs. Velocity

Speed is simply how fast you are travelling…

Velocity is “speed in a given direction”…

This car is travelling at a speed of 20m/s

This car is travelling at a velocity of 20m/s east


Speed Definition:

The rate of change of distance Equation:

speed = distance time

Units: m/s

Symbol: v (final) or u (initial)

Mnemonic: Xylophones are Very Terrible

x

tv


Acceleration 07/05/23 Definition:

How quickly velocity changes Equation:

acceleration = (final velocity – initial velocity) ÷ time a =(v-u)

t Symbol: a Units: m/s2

Mnemonic: A Changing Vulture

undergoes Therapy

v-u

ta


•a stationary object•An object with a fast constant velocity•An object with a slow constant velocity•an object which is accelerating

•The gradient of a distance time graph is its velocity•ie distance divided by time

x

t

x

t

x

t

x

t

Distance Time Graphs


What does the graph show?


•An object with a constant velocity•An object with a fast constant acceleration•An object with a slow constant acceleration•an object which has a changing acceleration

•The gradient of a velocity time graph is its acceleration•ie velocity divided by time

v

t

v

t

v

t

v

t

Velocity Time Graphs


What does the graph show?


Calculating acceleration from graphs


Calculating Distance Travelled

Sketch the graph in your books and write the answers


Definition Symbol

Unit

How far an object has movedHow fast an object is travelling initially

final velocitya

Mnemonic EquationXylophones are Very TerribleA Changing Vulture undergoes Therapy

Distance Time GraphsGradient = _____________

Velocity Time GraphsGradient = ___________, Area under = ____________

x(m)

t (s)

10

10

15

5

D

E

00

5

G

v (m/s)

t (s)

10

10

15

5

F

00

5

K

v (m/s)

t (s)

10

10

15

5

HI

00

5

Description

Speed

A

B

C

C

x (m)

t (s)

10

10

15

5

A

B

00

5

Description

Speed

D

E

Description

a

F

G

Description

a

H

I

K

Distance Travelled =

Distance Travelled =

Bv (m/s)

t (s)

A

C

DE F

The graph is of a sky diver, describe what is happening:________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________

Worksheet


Definition Symbol

Unit

distance How far an object has moved x minitial velocity

How fast an object is travelling initially

u m/s

final velocity How fast an object is travelling finally

v m/s

acceleration Change in velocity a m/s2

Mnemonic EquationXylophones are Very Terrible x = v tA Changing Vulture undergoes Therapy a = (v-u)/t

Distance Time GraphsGradient = Velocity

Velocity Time GraphsGradient = acceleration, Area under = distance

x(m)

t (s)

10

10

15

5

D

E

00

5

G

v (m/s)

t (s)

10

10

15

5

F

00

5

K

v (m/s)

t (s)

10

10

15

5

HI

00

5

Description

Speed

A Constant v

2 m/s

B Stationary 0 m/sC Coming

Back Constant v

-2 m/s

C

x (m)

t (s)

10

10

15

5

A

B

00

5

Description

Speed

D Constant v

0.5 m/s

E Faster constant v

1 m/s

Description

a

F Constant v 0 m/s2

G Decelerating

-2 m/s2

Description

a

H Constant a 1 m/s2

I Stationary 0 m/s2

K Constant a 1 m/s2

Distance Travelled = 125 m

Distance Travelled = 75 m

Bv (m/s)

t (s)

A

C

DE F

The graph is of a sky diver, describe what is happening:At A he is accelerating due to his weight, as his speed increases the air resistance increases until at B they balance and he reaches a constant velocity called the terminal velocity. At C he opens his parachute and the air resistance increases causing him to decelerate at D. At E the forces are balanced again and he falls at a new lower terminal velocity until at F he lands


Exam Question


Forces


What is a Force?


Drawing Vectors

Small Force

Going Right

Big Force

Going Right

Tiny Force

Going Left

Huge Force

Going Down


Cardsort: Types of Forces• Upthrust:

• upwards force on a body caused by the water being displaced around it. This is sometimes called buoyancy.

• Lift: • upwards force on an aeroplane.

• Thrust: • forwards force created by a body.

• Weight: • Force due to gravitational attraction.

• Friction:• Force caused by rubbing of surfaces that opposes motion.

• Air/Water Resistance:• Frictional Force caused by particles colliding with the body that

opposes motion.• Magnetic:

• Force caused by magnetic attraction.• Electrostatic:

• Force caused by attraction between charges.• Reaction:

• Force created by a body as a reaction to a force being applied.


What are the Balanced Forces?


Newton’s First Law Definition:

An object will remain at rest or at a constant velocity in a straight line unless there is a resultant force acting on it.

Isaac Newton 1643-1727


Calculating resultant forces




Newton’s Second Law• Definition:

• The net force acting on a body is directly proportional to the mass x the acceleration of the body and acts in the same direction.

• Equation: • F = m x a• N kg m/s2

• Mnemonic:• Fear my anger

Isaac Newton 1643-1727

F

am

If the forces acting on an object are unbalanced then the object will accelerate, like these wrestlers:


Gravitational Field Strength• Definition

• Acceleration due to a gravitational field. Can be measured in N/kg or m/s2.

• Is 10 N/kg on Earth.• Symbol:

• g• Equation:

• W = m x g• N kg m/s2

• Mnemonic:• Wow my goodness• Wazzup my G

W

gm

Worksheet


• Friction always acts in the opposite direction to the way an object is moving.•What is the direction of friction for the following moving objects?

Direction of Friction


Terminal velocity of a skydiver


Velocity–time graph of skydiver


Thinking Distance

Braking Distance

Stopping Distance

Stopping Distance =

= Thinking Distance +

Braking Distance

+


Factors affecting stopping distances

Copy into your book and add:mass of the car


Stopping distances


Moments a moment is a turning force about a point. moment about a point = force x distance If an object is balanced the sum of the moments on it must add

up to zero. Moments clockwise = moments anticlockwise

“Give me a place to stand and I will move the Earth”

Archimedes(287 – 212 BC)


Drag and drop any of the masses onto the “see – saw” and try to get it to balance. The masses are in kilograms and the distance in metres.

Principle of MomentsSeparate Science


Centre of Gravity The weight of an object acts through the centre of

gravity. If you balance an object the moments on it are zero. Therefore the centre of gravity must be at the pivot

point when balanced


Load (N)

Extension (cm)

Load extension

Elastic limit

Plastic region

Extension of a metal


Mnemonic Equation UnitsFear my AngerWow my GoodnessMoment = _______ x ________

Stopping distance = ______________ + ______________

Force Descriptionupwards force on a body caused by the water being displaced around

it..upwards force on an aeroplane.

forwards force created by a body.Force due to gravitational attraction

Force caused by rubbing of surfaces that opposes motionFrictional Force caused by particles colliding with the body that

opposes motionForce caused by magnetic attraction.

Force caused by attraction between chargesForce created by a body as a reaction to a force being applied.

Thinking Distance Braking Distance

Load (N)

Extension (cm)

________________________________

______ limit______region

• Definition: • A force is a

_____, _____ or _____ that can cause a change in motion, shape, or direction.

• Symbol:• F (_______)• W (_______)

• Units: • N (_______)

Worksheet


Force Description

Upthrust upwards force on a body caused by the water being displaced around it..

Lift upwards force on an aeroplane.Thrust forwards force created by a body.Weight Force due to gravitational attractionFriction Force caused by rubbing of surfaces that opposes motion

Air/Water Resistance

Frictional Force caused by particles colliding with the body that opposes motion

Magnetic Force caused by magnetic attraction.Electrostatic Force caused by attraction between charges

Reaction Force created by a body as a reaction to a force being applied.Mnemonic Equation UnitsFear my Anger F = m a N = kg m/s2

Wow my Goodness W = m g N = kg N/kgMoment = force x distance Nm = N mStopping distance = braking distance + thinking distance m

Thinking Distance Braking DistanceSpeed of Car Speed of Car

Tiredness Tyre ConditionsAlcohol Brake Conditions

Drugs and Medicines Road ConditionsDistractions (mobiles) Weather Conditions

Mass of Car

Load (N)

Extension (cm)

Load extensionHooke’s Law is Obeyed

Elastic limit

Plastic region

• Definition: • A force is a

push, pull or twist that can cause a change in motion, shape, or direction.

• Symbol:• F (force)• W (weight)

• Units: • N (newton)

Find the Resultant Force:


Crossword

Documents

forces powerpoint revision - Island Physicsislandphysics.wdfiles.com/local--files/igcse/forces.ppt · PPT file · Web viewForces Revision Syllabus Motion Forces * Boardworks GCSE