in motion - ms martin's grade 10 science€¦ · seconds minutes •hours 3^oo to i v^oo 30...

$: In Motion - Ms Martin's Grade 10 Science€¦ · Seconds Minutes •Hours 3^oo to I V^oo 30 0-5 $\oo 2.25 360 12 Time Distance Speed 20 m 4 m/s 1.8 s 20 m/s 1.5 h 200 km 3.5 h 5 km/h$
In Motion

In order to develop on understanding of the physics of motion, the outcomes

of this cluster ore exomined within the context of the automobile. The

relationships among displocement, velocity, acceleration, and time are

analyzed in conceptual, numerical, graphical, and symbolic modes. You will

investigate the qualitative aspects of inertia, force, impulse, and momentum

os they relate to automobile safety. The conservation of energy in cor

collisions and braking distance is explored. Using the knowledge you have

gained, you will use the decision-making process to address an ST5E issue

related to safe driving conditions.

Specific Learning Outcomes

•J Analyze the relationship among displacement, t ime, and velocity f o r an object in

uniform motion.

~J Collect displacement data to calculate and graph velocity versus t ime f o r an

object tha t is accelerating at a constant rate.

Analyze the relationships among velocity, t ime, and acceleration f o r an object tha t

is accelerating at a constant rate.

* Outline the historical development of the concepts of fo rce and "natural" motion.

'J Experiment to i l lustrate the e f f e c t s of inert ia in car collisions.

'•-S- bescrlbe qualitatively how force is related to motion.

~* Invest igate and describe qualitatively Newton's Thi rd Law.

* Define momentum and impulse and qualitatively relate impulse to change in

momentum fo r everyday situations.

-f Invest igate the conservation of energy in a motor vehicle collision.

* Invest igate conditions tha t i l lustrate the e f f ec t s of f r i c t ion on motion.

y Invest igate the fac tors tha t influence braking distance.

y Using the relationship among displacement, velocity, and f r i c t ion (d = k v 2 ) ,

calculate the braking distance of a motor vehicle.

( ONI AOTtLPMo^? '

Gr. 10 Science Page 2 I n Motion

Unit Conversions

I n th is unit you will be working with various units. You will need to know how to

convert between these units. To do th is, we will use conversion fac tors .

Distance

1000m - 1km

c m - - - - - cv

100cm = 1m 1000mm = lm

Examples:

Convert 36 m to km. : » vXfc v j - r - w v f ^ - ^ . ' r f j r . ; ^ v ^ i ; * | v x

- • ' w y r </. u * r J

— i !

Convert 1.2m to cm

K J

y

Tim

lm in = 60s

-~~""* ;

Examples:

Convert 35min to seconds.

5 5

Ih r = 60min

^ — - 0S* .

Ih r - 3600s

1

Convert 4.5hr to seconds

- — * - - - >_rr. - ' t z c x - - • ? I r m ^


Unit Conversions

Complete the following charts on conversion.

Centimeters Meters Kilometers

10 0- \ 0 .ool

52 0 . O 5 Z 0.85 0 . ooo12>5

YAo O O O 1.4

3280

Seconds Minutes •Hours

3^oo t o I

V^oo 30 0 - 5

$ \oo 2.25

360

12

Time Distance Speed

20 m 4 m/s

1.8 s 20 m/s

1.5 h 200 km

3.5 h 5 km/h

50 000 m 100 km/h

40 s 0.28 km

1 5 0 m O lSlOn 80 km/h

fir. 10 Science Page 4 In Motion

Introduction

Motion

• Defined as the movement of an object , or any of i ts parts, f rom one place to

another,

• The study of the motion of objects and the forces tha t a f f e c t the i r motion is

called mechanics.

• Mechanics is divided up into two dist inct categories:

i. kinematics

ii. dynamics

Kinematics

• Description of the motion of objects without considering the cause of the motion.

• Kinematics answers the following questions:

o I s i t moving fas t or slow? I s i t moving at a constant speed? I s i t at rest?

• Examination of the causes of the motion and an explanation of why the objects

move as they do.

• Dynamics answers the following questions:

o Why is the object speeding up or slowing down? How does something turn?

I n order to describe motion accurately we will study relationships between aspects

of motion. Relationships in physics can be described using:

1. Pictures (Diagrams) - a visual representation of what has happened

2. Words - a wr i t ten statement of what has happened

3. Numbers - a table of values obtained f rom an investigation of the relationship.

4. Graphs - p lot ted points

5. Equations (symbols) - mathematical representation showing how one variable

What direct ion is i t travelling? Moving?

a f f ec t s the other.


Uniform Motion

Scalar Quantities • have magnitude (size) but not direction

• distance, t ime, speed

Distance

• measures the tota l length of a journey along every twist and tu rn of the path

• standard unit : metre (m) ~ ^ -/< ( X t - ^ ^ ^ * 1

• represented as "d " - ^ *

• change in distance - f inal distance - initial distance 3- ^s

Ad = d f - d,

Time

• describes when an event occured

• standard unit: second (s)

• represented as " t "

• t ime - f inal t ime - initial t ime

At = t f - ti

Speed

• describes how fast something is moving

• standard unit: metres per second (m/s)

• represented as V

Gr. 10 Science Page 6 In Motion

Uniform Motion

Vector Quantities

• physical quantity tha t has both magnitude (size) and direct ion

• represented by an arrow over the symbol

• position, displacement, velocity, acceleration

Position

• place or location where an object is in relation to a reference point

• reference point is called the origin (where you s tar ted)

Displacement

• how much an object's position has changed

• standard unit: metre (m)

• displacement - f inal position - initial position _ . ^ ^ ^ ^

Acf= "df- d| v . _ . _ y

• labelled as positive (+) or negative (-) in relation to the origin

• another way to measure the direct ion of displacement is by using the Cartesian

coordinates of north, south, east, west

Velocity

• describes the speed and direction of motion

• describes how fas t an object's position is changing

• A\T= Vf - v, • standard unit: metres per second (m/s)

_ A d v = — j .

A t v J

Acceleration

• how much an object's velocity changes in a certain t ime

• can speed up, slow down, change directions

• standard unit: metres per second in each second (m/s 2 )

V f " V,

V )

: 5


Distance & Speed

Distance: how much around an object as covered

Speed: how fast an object is moving

Displacement & Velocity

Displacement: how far out of place an object is in relation

to its origin

Velocity: the rate at which an object changes its position

7- LUhat is the displacement of the cross-country team if they begin at school, run

10km and finish back at school? Q\jpf)

LUhat is their distance?

If the run took them 7 hour to complete, what is their velocity?

LUhat is their speed?

T * I

2- LUhat are the distance and the displacement of the race car drivers in the Indy

500?

If the 2073 winner, Tony Kanaan, finished the race in 2-67h, what was his speed?

On mph) | S 9 . - 2 ^ m p W

LUhat was his velocity?

Gr. 10 Science Page ffi I n Motion

3- in the 2012 Olympics in London, Usain Bolt ran the 100m race in 9-63s- UJhat

was his speed?

UJhat was his displacement? His distance?

l O o r n | o o n o

UJhat was his velocity?

Lf' If a speed skating oval is WOm and Clara Hughes raced in a 500m race, what

would her displacement be? Her distance?

If her time in the 500m race was H1-19s, what was her speed?

Gr. 10 Science Page ^ \ I n Motion

Distance, Speed & Time Practice Questions ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^

Remember-, k m / h -» m/s

f ~ D = ] m/s 4 km/h

••, 3.6

••••••••••••••••••••••mi

1. A gir l cycles f o r 3 hours at a speed of 40km/h. What distance did she travel?

Step 1 : Which formula do I use? (What is the missing information in the question?)

b - \ r- f

Step 2*. I den t i f y the information tha t is given? Does this match what you think

the question is asking?

D= ?

v= ^otm lb Step 3: Use the formula and f ind the missing information! Show your work and

don't fo rge t your units!!! Put a square around your final answer so tha t i t is easily

identif iable.

2. A car travels at a distance of 540km in 6 hours. What speed did i t travel at? b 7

Step 1 :

V- b / T Step 2:

D= ^ O f C r n

T= hh

v= 7

Step 3:

T b


3. John is a runner. He runs the 100m sprint in 10.6s. What speed does he travel at ,

in m/s? 1

Step 1 :

V.. \j n Step 2 :

v= ? Step 3:

I i oc-> — — — J

4. A cyclist travels 20km in 4h. What speed did the cyclist cycle at , in km/h? I n m/s? L r ?

Step 1 :

v - & r r

Step 2 :

T= n.

v= ? Step 3: ^

5. The distance between two cit ies is 144km and it takes Andrew 3h to travel

between these cit ies. What speed did Andrew travel at? ^ f

Step 1 :

Step 2 :

T= 3h v= ? Step 3:

r 3


6. A bus travels f rom Winnipeg to Regina, a distance of 576km away, in 6hrs. The bus

is only allowed to travel at a maximum speed of 90km/h. Did the bus break the speed

limit?

Step 1 :

Step 2 :

v= 7 Step 3:

1 ' * / fi

7. Lauren walks 100m in half a minute. What must her speed have been to travel this

distance? 5c ^

Step 1 : V TV ' '

Step 2 :

D= l o o m

T= l t ) < ;

v= ? Step 3:

f " J O

8. A mouse runs at a distance of 2m in 15s. What is it's speed?

V-.r> 2.

9. J im travel led at a speed of 18km/h f o r 2h. What was the distance covered?

&r, 10 Science Page 12 In Motion

10. A whale swims at a constant speed of 8m/s f o r 17s. What distance did i t travel?

11. How long does i t take to travel a distance of 672km at a speed of 96km/h?

v l b

12. Neil travelled 36km at a speed of 8km/h. Grant travelled 48km at a speed of

lOkm/h.

a) Whose journey was quickest? 7 "z

Ui • r -s . h

T o "

b) By how many minutes?

14. I f you run at 12m/s f o r 15 minutes, how fa r will you go?

^ - ^ ^ k>t\JU4 ft) Cf i a ^ c

IV- ' - j D t O O f O n


Speed and Velocity Calculations

V = Ad

At

1. A student rides a bicycle along a stra ight road f o r 30.0 s. She travels 254 m away

f rom her home. Find the speed she is travell ing at.

(;

2. A car is moving east, at 90 km/h, along a stra ight highway. Find the distance the

car has travelled a f t e r 1.2 h.

3. A person is walking west at 4.2 m/s. How long will i t take the person to go 110 m

west?

A - mm

i b

1 /

! 0

42 s

Gr. 10 Science Page 1^ In Motion

Speed and Velocity Calculations

4. A student is walking with a constant velocity along a st ra ight sidewalk. A t a t ime

of 1.4 s, his position is 31.4 m. Later, at a t ime of 6.1 s, his position is 9.6 m.

a. What is the student's velocity?

-r-r

b. What is his position at 4.4 s?

i

c. A t what t ime is the student's position 12.0 m?

- / Z D o i / 2 ' ° / a - - W i i

Gr. 10 Science In Motion

Pos/t/on-T/me graphs

I n a harness race, horses pull small carts with drivers around a track. The race begins

f rom a running s ta r t : tha t is, the horses do not s ta r t f rom rest. Examine the data f o r

two horses as they run through the straight portion of a t rack. Graph the motion of

each horse.

Time (s)

Position (m)

Time (s)

Position (m)

Time (s) Horse 1 Horse 2 Time (s) Horse 1 Horse 2

0 0 0 3 45 30

1 15 10 4 60 40

2 30 20 5 75 50

| Co

<4

^0

t*4

6

10

6

p \

>

I

— —

r

— — — — —

+

_ _ — — — — — —

/

>

1 — •)

1 !

'

, [

1 _

— — - • — — — ___ — ____ —

— — — — — — — — — — —

2-Gr. 10 Science

3 Page 16

4 In Motion

Pos/t/on-T/me Graphs

1. Calculate the velocity of each horse.

Velocity of horse 1 - Velocity of horse 2 =

t o • - - -

1

2. Which horse travelled f a r t he r in the 5.0 s? \ ^ ' -

3. Which horse had the greater speed? Why?

4. Explain how you can tel l which horse was moving fas ter f rom

a. the table C M S ^ O L O^EtT^d j r l j(k(J\ \£C&r4

b. the graph 5k)^b 5^ jVu.J.yrtJt

5. Describe the motion of each horse.

6. a. Find the position of horse 1, 8.0 s f rom the s ta r t .

<-•- • V ) c t

b. Use another method to f ind the position of horse 1, 9.0 s f rom the s ta r t

Sr. 10 Science Page 17 In Motion

fosition-Tlme Qro phs

Sample ftofrlem Calculating Average Speed:

Position as a function of time

Position

(m)

20 40 60

a) Calculate the average speed of

the object during each time

interval.

X: ? > - F J S t o - T e n

b) How was the object 's motion

changing as t ime went by?

u

c) What would the graph look like i f

the object was speeding up at a

smooth, steady rate?

V if /

&r. 10 Science Page 18 In Motion

fos/tion-T/me (frophs

The graph below shows the position of a student in the hallway of his new school, trying to

find his class for the f i rs t time. Assume that right is the positive direction, lef t is negative

Position 10 (m)

as usual.

During what time interval was the student moving the fastest?

t = to t =

From t = 15 to t = 18, was the student moving to the left or to the right?

Find the speed of the student from t = 18 to t = 27.

During what time interval(s) is the student stopped?


Distance-Time graphs

a UJ w o c a +-v\

a

AO

35 -1

30 .. 25

20 • •

15

10 .. 5

0 0

-5

-10 .. -15

1 «AX \\

(

H 1 • . y

10

Time (s)

15 20

a. Where does the object s tar t?

b. When does the object reach the reference point?

c. Where is the object at t=13 seconds? 4 % r '*

d. What is the speed of the object during the f i r s t 3 seconds?

e. What is the speed of the object during the interval f rom t=8 to t=13 s?

- ' '. j ~ O r I

f. When is the object at rest?

g. What is the average speed of the object during the f i r s t 8 s?

2

h. What is the average speed of the object during the t ime interval t=8 to t=15 s?

-Tfr-fjJ (il^A^U - 10 no-- 2o^

}


Pistonce-Ume Graphs

80 T

v

Time (minf^

a. What is the velocity (m/s) of the object during each section of the t r ip?

- - - - - - f 0 - i b D

/ 5 V " i f : 3 c kYll To

b. When is the object at rest? ¥ " r < £ 0 ^ : ' I P - i i P x .

c. When is the object moving to the East? - °\Q%

d. What is the average velocity of the object f o r the f i r s t minute of the t r ip?

1

fcO . -A

e. What is the average velocity of the object f rom t = 1.5 min to t = 3 min?

r J i*<j\ - .

\% - i^ 1 D ' ' - - - - -

Sr. 10 Science Page 21 In Motion

Distance-Time graphs

f. What is the average velocity of the object f o r the ent i re t r ip?

g. What is the to ta l distance traveled by the object?

h. What is the displacement of the object at t = 2 min.?

6 :• MOYVX I s


Acceleration Calculations

v f - v, a = -—•—

1. A student s tar ts f rom rest and reaches a velocity of 7.1 m/s to the r ight of the

observer in 5.2 s. Find the student's average acceleration.

2. An airplane is f ly ing at 210 m/s. I t slows down to 165 m/s in 12.3 s. Find the

acceleration of the airplane.

3. A ball is rolling along an incline at 7.2 m/s to the r ight. A f t e r 9.3 s, the ball is

rolling at 3.9 m/s to the le f t . Find the acceleration of the ball.

vf-- i'lvnK r i ., •


Acceleration Calculations

4. Jan accelerates her car f rom rest at a rate of 3.0 m/s 2 f o r 5.0 s.

a. What is the final speed of Jan' car a f t e r 5.0s?

tf- 3-OmK2 3-0 = v y - o

• !_:.. J

b. She then maintains th is speed fo r another 35 s, how fa r does Susan travel

during this time?

J

£r. 10 Science Page 24 In Motion

Aristotle, Galileo & Newton

A r i s t o t l e

384 BC - 322 BC

Greek Philosopher - a student of Plato, one of the great philosophers of ancient Greece

Vou may have heard of him...

• Aristotle was the guy responsible for the theory that everything was made of:

o Earth o Wind o Fire o Water

An aristocrat - his father was the personal physician of the king of Macedonia.

His parents died when he was 10 - he was raised by foster parents

^ A highly respected academic, Aristotle was responsible for the death of atomic theory for more than 2000 years! A guy named Democritus proposed that everything was made of small pieces called atoms, but Aristotle said that everything is made of the four elements earth, wind f i re A water!" and so respected was Aristotle that the idea of

The. Physics of Aristotle:

• I f you want something to move, you have to push on it. I f you stop pushing, the object stops moving.

• Objects tend to move towards the center of the universe, namely Earth. This was called "Natural Motion"

• Projectiles move because of air rushing in behind and pushing them forward.

atoms disappeared until 1810 when Dalton re-introduced them to the world with his "new" atomic theory!


Aristotle, Galileo & Newton

Galileo Galilei

1564 -1642

Invented the telescope

Discovered sunspots

Discovered the 4 largest moons of

Jupiter

Studied falling objects and suggested

that all objects fall towards the earth at

the same rate (regardless of weight).

Published a book explaining that the sun

was the centre of the solar system, not the earth.

fife Crime?

Publicly advocating that

the sun, not the earth,

was the centre of the

solar system as Biblical

interpretation of the

Did you know..

Galileo was almost

executed by the Church

during the time of the

Spanish Inquisition

Jntertic One of Galileo's greatest contributions to physics was his formulating the concept of inertia.

The inertia of an object is a measure of how diff icult it is to change its motion.

A piano that is sitting still is hard to get moving. A toaster sitting at rest is easy to get moving.

Thus the piano has a large inertia while the toaster's inertia is much less.

Similarly, a semi-truck flying down the highway at 111 km/hr is hard to slow down. A mosquito

flying at 111 km/hr is not so hard to slow down. The truck has a lot of inertia; the mosquito does


Aristotle, Qolileo & Newton

Sir Isaac Newton

1642 - 1727

Did you know*

Newton was a member of Parliament in Britain on

two dif ferent occasions. He finished his working

career not in

the field of science,

but working as the

"Master of the Mint"

where all of Britain's

Built on Galileo's thoughts to create three laws of motion

Formulated the law of universal gravitation, explaining that gravity was responsible for both the falling of objects here on earth and for the revolution of the planets around the sun.

Created equations and theories that explained light's behaviour. He also invented the f i rs t reflection telescope.

Invented a new type of mathematics, now known as Calculus.


Newton's first Low

Isaac Newton described acceleration as an imbalance in forces. For example, i f there

is a force acting on your r ight side but there is a stronger fo rce acting on your le f t

side, you will be moved to the right. Newton devised a law of physics tha t is st i l l

accepted today.

An object at rest stays at rest, and an object in motion stays in

motion, unless the object is acted upon by an external and unbalanced

force. v _ , ,, . ^ . . ,. _ . _ .. _ _ _ _ _ ^

This characteristic of mat ter to resist changes in motion is called inertia. This is why

Newton's First Law is o f ten referred to as Newton's Law of Iner t ia .

W I T H N O O U T S I D E F O R C E S T H I S O B J E C T W I L L N E V E R M O V E

W I T H N O O U T S I D E F O R C E S T H I S O B J E C T W I L L N E V E R S T O P


Newton's Second Low

• I n Newton's Second Law, we are considering the relationship between an ob ject 's

mass and its acceleration. The mass of an object is not simply the quantity of

matter , as Newton himself theorized. The mass of an object is actually a measure

of inertia of an object.

• The more mass an object has, the more d i f f i cu l t i t becomes to change the

ob ject 's state of motion

• For example, i t is more d i f f i cu l t to budge a piano f rom rest than a piano bench.

This is because the piano has more inertia than the bench does and much more

mass.

Newton's Second Law is o f ten stated as:

( F = ma

F - net fo rce (Newtons (N) or kg*m/s 2 )

m - mass of an object (kg)

a - acceleration (m/s 2 )

• A force is any kind of push or pull on an object. Simply applying a fo rce does not

mean tha t an object will move. You can push as hard as you can on a wall and never

move i t .

• The law also implies tha t , to achieve a certain acceleration, the amount of applied

fo rce is somehow related to the mass of an object. The more massive an object

becomes, the greater the fo rce necessary to change its speed—hence its

acceleration.

• Newton's Second Law states tha t a force is capable of changing the direct ion of

motion on an object.

F = m a

TUB AAORE FOttCfc.. . T H E AAORfc A X X E i - t f t A n O N


Newton's Second Low

Examples:

1, What force is exer ted upon a 10kg mass if i t accelerates 1

Jf^lOOA/ 7

2. How much net fo rce is required to accelerate a 1000 kg car at 5.0$ m/s 2?

1 - 5t>ODf^ ' •

3. I f you apply a net fo rce of 1 N on a 200 g book, what is the acceleration of the

book? r ' : Z x %

m u.i. J

4. A f re igh t t rain slows down as it approaches a t ra in yard. I f a force of - 3 . 8x l 0 6 N

is required to provide an acceleration of -0 .33m/s 2 what is the train's mass?

-3 .y x /£>< 7 ----- - .

5. I f a 600kg racing Formula One car crashes into the barr ier at 85m/s (305km/h)

and it takes 3 seconds f o r the car to stop st i l l . What is the fo rce tha t the car hit

with?

L r ' ' - - ^ . 3 m h 2


Newton s Third Low

for every action there is an equal and opposite reaction.

Since forces always occur in pairs, e i ther balanced forces or unbalanced forces, t r y

to consider the "opposite" fo rce acting when a more obvious force is acting in an

everyday activi ty. Remember tha t unbalanced forces cause acceleration but there

will be no acceleration i f the forces are balanced

Example:

You prepare to jump while on a skateboard ... as you jump: -#£|Uix4 4(\U[ I *1

Action: Your fee t push down on the upper surface of the skateboard. O^pO^ jC 0( 1^tCh^ Reaction: The skateboard pushes up on your fee t wi th an equal but opposite fo rce

in pvu aiftdhc^

Action force - the fo rce tha t init iates the reactions

Reaction force - the fo rce tha t responds to the initial action.

s 4 ij

%1 I> 1Mb

Gr. 10 Science Page 31

Newton's Third Low

I n the following examples, see i f you can ident i fy the action fo rce and the reaction

force.

1. You jump out of the boat and onto a dock. The boat f loats backwards, moving away

f rom the dock.

Act ion force - ^ frtn; l l u L fa^rf fO JMl^ & doUt

Reaction force - [ j\L CkttillJiO^. k)0^(JCajA-¥iK

2. As you walk on the f loor , you push down on the f loor and the f loor pushes back up

against you.

Action force - LjhlA- p l A ^ h A f t U ^ QVN —pfnpy

Reaction force - '•'{'U ptA-JlM b<S.:V. %&j*U>-i! !lfJ~


Momentum

Momentum - the quantity of motion.

To bring a moving object to a stop, we must decrease the ob jec t 's momentum to zero.

I f we were to calculate momentum, we would multiply the mass of the object by the

velocity of the object.

The mathematical relationship f o r momentum is:

P - momentum (N*s or kg*m/s)

m - mass of an object (kg)

v - velocity (m/s)

Example:

What is the momentum of a 100 000kg t ra in moving at 5.0 m/s? What is the

momentum of a lOg toy car moving at 5.0m/s. Which one has the greatest amount of

momentum?

P = mv

TiroiLn-. :

P- 5oo oooAJ-^

. m


Impulse

How can we reduce an ob jec t 's momentum to zero? I n order to do th is, we must apply

an impulse.

Impulse - product of fo rce and t ime

The mathematical relationship f o r impulse is:

l = f t

I - impulse (N*s or kg-m/s)

F - fo rce of an object (N)

t - t ime (s)

Example:

An object has a momentum of 1000kg*m/s. What impulse is required to bring i t to a

stop? How much force is needed if i t stops in 1 second? How much force is required

i f i t stops in 2 seconds? I n 4 seconds? I n 10 seconds?

- / O O O r J

* f

bs jooo - loo M

What is the function of an air bag?

jo Step


Conservation of Energy

Law of Conservation of Energy - energy cannot be lost or created, but can only be

transformed or converted into d i f f e ren t forms of

energy.

I n a car collision, huge amounts of kinetic energy are converted and t rans fe r red to

other systems. Energy can be converted to several d i f f e ren t types of energy, such

as:

1. Kinetic energy: the energy of motion (ex. wheels turning)

2. Potential energy: the energy of position with respect to the surface of the Earth

(ex. an object fall ing f rom two storeys up will not fa l l wi th as

much fo rce or acceleration as an object tha t fal ls f r om 16

f loors up)

3. Heat energy: the energy of molecules on motion (ex. smoke rising f r om an engine)

4. Sound energy: the disturbance of molecules (ex. a loud crashing sound)

As the kinetic energy reduces to zero, other forms of energy increase.


The Effects of Friction

Friction - a force tha t opposes (acts against) motion.

Pushing force

The amount of f r i c t ion depends on:

i. The types of surfaces involved.

ii. The amount of contact between the two surfaces.

iii. The amount of fo rce acting on the two surfaces.

What are some examples of conditions tha t can a f f e c t f r i c t ion and motion on the

roads?

1. Road conditions: icy, wet, snow-covered (these can all reduce f r ic t ion) , gravel and

d i r t (can increase f r i c t ion , unless i t is very loose)

2. Type of vehicle: some cars are equipped with four-wheel drive and are made f o r

all conditions

3. Type of tire: snow t i res and studded t i res add t ract ion f o r more f r i c t i on , while

racing t i res are smooth f o r less f r i c t ion and more speed


Braking Distance

Braking (stopping) distance - the distance you cover while braking

- the distance required to stop a f t e r the brakes have

been applied

A person's react ion also has an impact on braking distance.

Reaction t ime -amount of t ime i t takes to recognize a situation and react to i t

•Human Factors that Increase Reaction Time

There are several fac tors tha t will Increase your reaction t ime and should be avoided

when driving.

1. Alcohol: Alcohol is a depressant and will slow down your reaction time.

2. Hallucinogenic drugs: These drugs inhibit t ransmi t ters fo r the nervous system

and will slow down your reaction time.

3. Depressant drugs: These drugs slow down your body act ivi ty, including reaction

t ime.

4. Driver fatigue: The more t i red you are, the slower you will process information

and respond to i t .

5. Cold/allergy medications: Many over-the-counter medications f o r the rel ief of

cold, f l u , and allergy symptoms contain active

ingredients tha t can a f f e c t reaction t ime. Some

antihistamines, f o r instance, produce drowsiness.


Broking Distance

• Braking distance is also a f f ec ted by the condition and type of driving surface.

• When there is more f r i c t ion between the t i res and the surface, then braking

distance is less (ex. Dry pavement).

• I f there is very little f r i c t i on , then more braking distance is required (ex. ice ).

• We can use the frictional constant, k, to indicate how much f r i c t ion exists f o r a

given surface. The closer the number is to zero, the more f r i c t ion there is.

The mathematical relationship f o r braking distance is:

Example:

Find the braking distance f o r a car with a velocity of 50km/h on dry pavement (k =

d - braking distance \nn

k - f r ic t ional constant

v - velocity yy\ \ ^

r d = *v 2

0.06).


Total Stopping Distance

• The calculation f o r braking distance does not take into account the react ion t ime

of the driver.

• I n order to give an accurate idea of actual braking t ime, we must add the distance

the vehicle travels while the driver reacts.

Reaction Distance - the distance travelled a f t e r the obstacle has been observed but

before the brakes are applied.

The mathematical relationship f o r reaction distance is;

d = vt

d - reaction distance

v - velocity of the object

t - t ime required to react.

Total Stopping Distance - the amount of t ime required to react and brake

Total Stopping Distance = Reaction Distance + Bracing Distance

Example: ^cM^^f^k ^ ^ The driver of a vehicle traveling at 80 km/h sees a ball roll into t r a f f i c . I f the

reaction t ime of the driver is 0.27 seconds and the surface has a k value of 0.12, how

much distance is required to stop the car?


in motion - ms martin's grade 10 science€¦ · seconds minutes •hours 3^oo to i v^oo 30...

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